***Useful Information For The Working Sparky***

[amberleaf]

17th Edition Wiring Regulations Practice : Apprentice ,
Overall Percentage Score , 100%

Unit 1: Special installations or locations ( 100% )
Q1 : Zone O in a bathroom is the ( A ) Area within the bath or Shower , ( p-165 701.32.2 )
Hint !! Extreme end ,
Q2 : Zone 1 in a bathroom is the
Hint !! Not quite the extreme end , ( A ) Area directly above the bath or shower up to 2.25m above finished floor level . ( p-165 701.32.3 )
Unit 2 : Appendices ( 100% )
Q2 : BS-1362 relates to ( A ) Cartridge fuses for use in 13A plugs , ( p-229 BS – Standards )
Hint !! Used with BS- 1363
Unit 3 : Inspection & Testing ( 100% )
Q3 : An insulation Résistance test performed on a 50v a.c . SELV installation should be capable of producing a test voltage of
( A ) 250v dc ( p-158 / table 61 )
Hint !! think about ELV downlighters and the average voltage they use ,
Testing : Q 21 : An insulation résistance test performed on a 230v a.c installation should be capable of producing a test voltage ,
Hint !! what type powers the instrument ? ( A ) 500v DC ( p-158 / table 61 )
Unit 4 : Definitions ( 100% )
O4 : A double insulated hand held electric drilling machine is known as
Hint !! think about where you see the symbol , ( A ) Class II equipment ,
Q5 : BS-7671 IEE Regulations define Extra Low Voltage a.c as Not exceeding ( A ) 50 volts a.c , ( p-31 )
Unit 5 : Selection & erection of equipment ( 100% )
Q6 : where a wall consists of a metallic construction and it is necessary to install cables within that wall , the circuit should
( A ) be RCD protected ,
Unit 6 : protection for safety ( 100% )
Q7 : A device intended for safety reasons to cut off all or part of an installation from every source of electrical energy provides ,
( A ) Isolation ( 537 / 537.2 )
Q8 : what is the maximum Zs for a 32Amp type B circuit breaker protecting a standard ring final circuit ,
( A ) 144Ω ( p-49 / table 41.3 )
Unit 7 : Scope , Object and fundamental characteristics ( 100% )
Q9 : Inspection & Testing of an installation should be completed by ( A ) Competent person )
Hint !! Maybe someone who knows what they are doing :
Q10 ; BS-7671 is a ( A ) Non-Statutory document ,
Hint !! its Not enforceable in Law ,
Unit 8 : Assessment of general characteristics ( 100% )
Q 11 : Non-sheathed cables for fixed wiring , other than protective conductors , should be installed in , ( A ) Conduit or Trunking ,
Q 12 : who is responsible for specifying the first periodic inspection on an installation ?
Hint !! who knows everything about an installation before the Other ?
( A ) the person responsible for the design ,
Q 13 : Inspection & Testing of an installation should be completed by ?
Hint !! maybe someone who knows what they are doing ,
( A ) Competent persons ,
Q 14 : Basic protection protects against ?
Hint !! the most basic of contact ,
Electric shock under fault free conditions ,
Q 16 : Any overcurrent protective device installed at the origin of a circuit must have a breaking capacity of ?
Hint !! what cases the maximum current to flow under fault conditions ,
( A ) Equivalent or more to the prospective short circuit current ,
Q 17 : Non-sheathed cables for fixing wiring , other than protective conductors , should be installed in ,
Hint !! think what the sheathing provides on cable , ( A ) Conduit or Trunking ,
Q 18 : Undervoltage protection is required where the restoration of power may cause ,
Hint !! what can be dangerous if power is suddenly turned on ?
( A ) Unexpected starting of machinery ,
Q 19 : outdoor lighting involves all the following except ,
Hint !! Temporary installation , ( A ) Festoon lighting ,
Q 20 : where a wall consists of a metallic construction and it is necessary to install cables within that wall the circuit should ?
Hint !! needs additional protection , ( A ) be RCD protected ,

 

[amberleaf]

PERIODIC INSPECTION REPORT FOR AN ELECTRICAL INSTALLATION
(REQUIREMENTS FOR ELECTRICAL INSTALLATIONS - BS 7671 [IEE WIRING REGULATIONS])
Extent and Limitations of the Inspection :
Extent of Electrical Installation covered by this report ,
Limitations ( see Regulation : 634.2 p-163 ,

Insulation resistance
If the DC resistance tests above fail to identify the cause of a circuit that is causing RCD tripping on its own (i.e. without the aid of the appliances usually connected to it). You may find that repeating the tests described using an insulation resistance tester will yield more information. Since the insulation resistance tester carries out the tests at much higher voltages than the multimeter (typically 500V) it will identify those few failures where the conduction path between a live conductor and earth is only visible at mains voltages.
Take care when performing these tests, it is possible to get a nasty shock off an insulation test meter!
Mitigating the effects of nuisance trips
While it is possible to eliminate most causes of nuisance trips with careful system design and testing, it is always wise to design the system to allow for the possibility of it happening:
* Provide dedicated non RCD protected circuits [see note] for vulnerable equipment such as:
*Freezers
* Central Heating Systems
* Heated Aquariums
* Fire or smoke alarms
* Security systems and lighting
* Computer and IT equipment
* Have as few circuits or devices as possible protected by the same RCD so that a trip impacts as few extraneous circuits as possible. The ultimate solution would use RCBOs for each circuit. Obviously expense has to be weighed against the implications of tripping.
* Use emergency lighting to backup any important lighting circuits that need to be RCD protected (i.e. on TT earthing systems). In particular these should include lighting for:
* Stairs
* Fire escape routes
* Near trip hazards or other difficult to navigate areas
* Near the consumer unit
* Consider using uninterruptible power supplies (UPS) to maintain running of critical equipment.
* Power failure alarms might also be an appropriate measure in some circumstances.
Note: With the advent of the 17th edition of the wiring regulations, one must comply with the requirement that any buried cables that don't have 30mA trip RCD protection, must still be adequately protected from physical damage. This can be achieved either via being buried at 50mm or greater depth in a wall, or with metallic earthed protection such as conduit or by using suitable metal sheathed cables like SWA, MICC etc. Note that new cable types are becoming available to help meet these requirements. Surface mounted cables may also be installed without additional RCD protection in some circumstances since it is assumed they are sufficiently visible to avoid accidental damage from drilling / nailing etc.
System design using RCDs
Some of the system design aspects of using RCDs to good effect are covered in the mitigation section above. However the following basic principles should also applied:
1. Use split load consumer units, to allow circuits that do not benefit from RCD protection to be powered directly.
2. Don't place too many circuits on the same RCD. In particular identify circuits that are likely to have high leakage (e.g. those containing lots of IT other electronic equipment).
3. Where RCDs need to be cascaded, use time delayed types for the upstream device so that trips are contained close to the cause of the fault.
4. Don't place circuits to outside electrics and outbuildings on the same RCD as protects the house circuits.
5. Avoid placing high leakage devices on RCD protected circuits where possible.
6. Design circuits such that the anticipated leakage is no more than 25% of the trip threshold. This will allow for later circuit extension.
7. Ensure accessories and wiring are not placed in excessively damp environments.
8. Don't use lower trip threshold devices that is appropriate for the level of risk present and protection sought.

NOTES ON COMPLETION OF MINOR ELECTRICAL INSTALLATION WORKSCERTIFICATE :

Scope :
The Minor Works Certificate is intended to be used for additions and alterations to an installation that do not
extend to the provision of a new circuit. Examples include the addition of socket-outlets or lighting points to
an existing circuit, the relocation of a light switch etc. This Certificate may also be used for the
replacement of equipment such as accessories or luminaires, but not for the replacement of
distribution boards or similar items. Appropriate inspection and testing, however, should always be
carried out irrespective of the extent of the work undertaken ,

Part 1 Description of minor works :
1,2 The minor works must be so described that the work that is the subject of the certification can be
readily identified.
4 : See Regulations 120.3 and 120.4. No departures are to be expected except in most unusual
circumstances. See also Regulation 633.1

Part 2 Installation details :
2 : The method of fault protection must be clearly identified e.g. earthed equipotential bonding and
automatic disconnection of supply using fuse/circuit-breaker/RCD
4 : If the existing installation lacks either an effective means of earthing or adequate main equipotential
bonding conductors, this must be clearly stated. See Regulation 633.2
Recorded departures from BS-7671 may constitute non-compliance with the Electricity Safety, quality
and continuity Regulations 2002 (as amended) or the Electricity at Work Regulations 1989. It is
important that the client is advised immediately in writing.

Part 3 Essential Tests :
The relevant provisions of Part 6 (Inspection and Testing) of BS 7671 must be applied in full to all minor
works. For example, where a socket-outlet is added to an existing circuit it is necessary to ;
1 : establish that the earthing contact of the socket-outlet is connected to the main earthing terminal
2 : measure the insulation resistance of the circuit that has been added to, and establish that it complies with Table 61 of BS 7671
3 : measure the earth fault loop impedance to establish that the maximum permitted disconnection time is not exceeded
4 : check that the polarity of the socket-outlet is correct
5 : (if the work is protected by an RCD) verify the effectiveness of the RCD

Part 4 Declaration :
1,3 The Certificate shall be made out and signed by a competent person in respect of the design , construction, inspection and testing of the work
1,3 The competent person will have a sound knowledge and experience relevant to the nature of the
work undertaken and to the technical standards set down in BS-7671 be fully versed in the inspection
and testing procedures contained in the Regulations and employ adequate testing equipment.
2 : When making out and signing a form on behalf of a company or other business entity, individuals shall state for whom they are acting ,

 

[amberleaf]

SELV and PELV :

According to IEC 60364-4-41 protection against electric shock is deemed to be provided when:
• the nominal voltage cannot exceed an upper limit in accordance with IEC 60449 (50 V AC / 120 V DC)
• the supply is from a safety isolating transformer in accordance with IEC 60742 or equivalent (e.g. motor generator with windings providing an equivalent isolation)
• an electrochemical source (e.g. battery) or another source independent of a higher voltage circuit (e.g. diesel-driven generator),
• mobile sources or certain electronic devices all complying with appropriate standards, where measures have been taken in order to ensure that, even in the case of an internal fault, the voltage at the outgoing terminals cannot exceed the above mentioned levels , or
• when all above conditions are fulfilled and in addition electrical separation with either SELV for unearthed circuits or PELV for earthed circuits is provided
Arrangement of circuits :

IEC 60364-4-41 states that live parts of SELV and PELV circuits shall be electrically
separated from each other and from other circuits. Arrangements shall ensure electrical separation
not less than that between the input and output circuits of a safety isolating transformer ,
Circuit conductors of each SELV and PELV system shall preferably be physically
separated from those of any other circuit conductors. When this requirement is impracticable, one of the following arrangements is required
• Plugs and socket-outlets of SELV and PELV systems shall comply with the following requirements
– plugs shall not be able to enter socket-outlets of other voltage systems : – socket-outlets shall not admit plugs of other voltage systems :
– socket-outlets shall not have a protective conductor contact :

Requirements for unearthed circuits ( SELV ) :
According to IEC 60364-4-41, live parts of SELV circuits shall not be connected to
earth or to live parts or to protective conductors forming part of other circuits
Exposed conductive parts shall not be intentionally connected to :
* earth; or
* protective conductors or exposed conductive conductors of another circuit; or
* extraneous conductive parts.
If nominal voltage exceeds 25 V AC r.m.s or 60 V ripple-free DC, protection against direct contact shall be provided by:
* barriers or enclosures affording a degree of protection of at least IP2X or IPXXB; or
* insulation capable of withstanding a test voltage of 500 V AC r.m.s for 1 minute ,
In general, protection against direct contact is unnecessary if the nominal voltage
does not exceed 25 V AC r.m.s. or 60 V ripple-free DC. However, it may be necessary under certain
conditions of external influences, which is currently under consideration by the IEC.

 

[amberleaf]

Why Earth ?
One side of the electricity supply (the neutral) is firmly connected to earth at the substation to prevent the supply 'floating' relative to earth for safety reasons.
Many electrically operated devices (e.g. washing machines, heaters and some lighting fittings) have exposed metalwork which could become live if a fault occurred. Anyone touching it could then receive a shock or even be killed depending on the current flowing through them to earth. To prevent this, an earthing conductor should be provided to all socket outlets, lighting circuits and any fixed appliances to which exposed metal parts are then connected. The earth connection limits the voltage which can appear on the exposed metal parts under fault conditions to a safe value until the fuse blows or the MCB or RCD trips. Note that earthing does not necessarily prevent anyone receiving a shock, but together with the time/current characteristics of the protective device (fuse, MCB or RCD) it should ensure that it is not lethal. It is desirable to make the impedance (resistance) of the earth wiring a low as practicable. (1000A flowing through 0.1 ohm drops 100V! )
Note that exposed metalwork cannot be protected by connection to the neutral because current flowing will cause a voltage drop between the metalwork and true earth. Also, if the neutral connection breaks or the appliance is plugged into a socket with line and neutral reversed (!), the metalwork will be at full mains voltage.
Appliances with an earth connection are called Class I (one): Class II or 'double insulated' appliances incorporate additional insulation to prevent exposed metalwork becoming live, and do not require an earth connection. This means that a 2-core mains lead can be used and internal earth connections are not needed.
A fundamental principle of electrical safety is that no single fault condition should cause a hazardous situation. This is why some of the regulations may appear to be rather stringent: it is better to be safe than sorry.
Who Supplies the Earth ?
The earth connection will usually be supplied by one of the following methods:
a). By the electricity company. Either through the armouring of the supply cable or through a combined neutral and earth conductor. The latter method is termed PME (protective multiple earthing) and requires some special attention (see below). There will usually be a label near the meter indicating a PME system.
b). Through an earth electrode; usually a rod or plate driven into the ground. This method is found where the electricity company cannot easily supply or guarantee an adequate earth conductor; for example, where the supply comes on a pair of overhead wires. The user is generally responsible for the adequacy of the earth electrode.
The method of earthing can normally be found out by tracing the wiring from the meter/consumer unit. It is usually fairly obvious. IMPORTANT! - It is no longer permitted to use a water or gas pipe for the main or only earthing connection. There may, however be earth bonding wires connected onto the water and gas pipes for 'equipotential bonding' (see below). If there is no electricity company earth or dedicated separate earth electrode, then one must be provided. Contact the electricity company if in any doubt.

Earthing of Electrical Installation :
Each circuit requires an earth conductor to accompany (but kept separate from) the line and neutral conductors throughout the distribution. Where the distribution is in the form of a ring, the earth connection must also complete the ring.
The bare tails of earth conductors must be insulated with green/yellow sleeving from the exit from the cable sheath to the earth terminal.
All metal boxes should be connected to the earth; either through a short tail covered with green/yellow sleeving to the socket earth terminal or directly by the earth conductor for a switch box.
Equipotential Bonding
As mentioned elsewhere, a fault current flowing in the earth wiring will cause the voltage on that wiring to rise relative to true earth potential. This could cause a shock to someone touching, for instance, the case of a faulty washing machine and a water tap at the same time. In order to minimise this risk, an 'equipotential zone' is created by connecting the services to the main earthing point. Such services are:
• Water Pipes
• Gas Pipes
• Oil Pipes
• Central Heating
• Metallic Ventilation Trunking
• Exposed Parts of Building Structure
• Lightning Conductor
• Any other Metallic Service

WHY DO LIGHT BULBS ALWAYS BLOW WHEN YOU SWITCH THEM ON, AND WHY DO THEY BLOW FUSES ?
An ordinary incandescent "light bulb" consists of a thin tungsten filament in a glass envelope containing an inert gas. The filament has a relatively high resistance, and thus gets hot - hot enough to give out useful amounts of light as well as lots of heat - when current is flowing through it. The inert gas prevents the hot tungsten rapidly oxidising, as it would in air, or rapidly evaporating, as it would in a vacuum. It does, however, reduce efficiency, by conducting heat away from the filament. (Different gases and pressures are selected for different applications: for example, krypton and xenon are advantageous because they convect less and prevent evaporation better than argon/nitrogen, and therefore allow a hotter, more efficient, filament to be used while maintaining lamp life. Note that quartz halogen bulbs are different again: here, evaporated tungsten is re-deposited on the filament, thus allowing it to be hotter still while maintaining its life.)
Tungsten, being a metal, has a resistivity which increases as its temperature rises. Therefore, when you switch on a lamp, it presents a much lower resistance than normal to the passage of electricity, and so your beefy electricity supply will drive through a great deal more current than normal while the filament heats up, putting it under thermal stress as it expands. This on its own encourages the filament to give up and break, but it is exacerbated by the fact that any thinned section will incur extra stress, as it will heat up more quickly than the rest of the filament (being thinner), present a higher resistance, and thus dissipate even more than its fair share of the (increased) power. This will tend to thin it further, rapidly, and hence lead to a point of failure.
How do you deal with it? Well, using a rotary on/off dimmer, where you always have to switch on the lamp at its lowest brightness, will help a lot. A dimmer will reduce the maximum available light output slightly. You can also fit negative temperature coefficient thermistors in series with the bulb. These have a resistance/temperature characteristic with the opposite slope to that of the filament, so give a "soft start" until they themselves warm up. Again, you will lose a little brightness, and waste a little energy in the hot thermistors. I am not aware of any "off the shelf" products containing thermistors, probably because they need to be selected for the wattage of lamp required.
It should be noted, however, that it is probably counterproductive to try to keep a light bulb alive for too long. This is because the thinned filament will be taking less current, so the light output will be reduced, and the tungsten that has evaporated from it will be deposited on the inside of the glass, reducing efficiency by blocking some of the light.
As regards blowing the fuse, this is never directly due to a broken filament falling onto the lead-out wires, and thus presenting a much lower resistance, but is due to the gas or vaporised filament in the bulb becoming ionised. The high temperature and large electric field (full mains voltage across a very small gap) which occurs when the filament breaks can cause the gas to go into a conducting state, and the plasma will "spread" until it shorts out the lead-out wires, because it presents a much lower resistance than the filament. This causes a "pop" due to rapid heating, and has been known to cause the envelope to explode. Light bulbs usually have built-in fuses to deal with this, but as they are built down to a price, they aren't always effective.
If you plug in a new light bulb and it only lasts a few seconds, leaving a white pattern on the glass, this is because it has cracked at some point, letting air in. When energised, the filament has oxidised to white tungsten oxide, which condenses on the glass in a pattern corresponding to the flow of air inside as the lamp is switched on.
Oh, by the way, "extra-long life" bulbs seem to be a con. They just run at a lower temperature than normal bulbs, thus lasting longer, but being a lot less efficient. There is no justification for the extortionate prices charged for them.

 

[amberleaf]

Cables in contact with polystyrene

Do not let electrical cables come into contact with polystyrene. It slowly leaches the plasticiser out of the PVC, so that it becomes stiff and brittle. Sometimes it looks like the PVC has melted and run a little.

* Shaver sockets incorporate special isolating transformers which provide an earth-free output. The primary (input) side requires an earth which is connected internally to the transformer core.

Protective Multiple Earthing (PME.)
With PME. the neutral and earth conductors of the supply are combined. The supply company connects the neutral solidly to earth frequently throughout the distribution network. At the customer's connection point the company supplies an 'earth' (which is actually connected to the neutral) to which all the installation earths and equipotential bonding are connected. Note that within the installation, the earth and equipotential bonding are kept separate from the neutral in the usual way.
With PME. there is a potential danger in that if the combined neutral/earth conductor of the supply became broken (very unlikely but nevertheless possible), the voltage on the earth conductors could rise towards the full supply voltage. It is most important therefore that equipotential bonding is rigorously applied in installations supplied by PME. The minimum size of main bonding conductor is 10 sq mm but may need to be up to 25 sq mm depending on the size of the incoming neutral/earth conductor: the supply company will advise you.
Electricity System Earthing Arrangements
Mains electricity systems are categorised in the UK according to how the earthing is implemented. The common ones are TN-S, TN-C-S and TT. You will sometimes see these referred to in questions and answers about mains wiring.
Note that in these descriptions, 'system' includes both the supply and the installation, and 'live parts' includes the neutral conductor.
First letter:
T The live parts in the system have one or more direct connections to earth.
I The live parts in the system have no connection to earth, or are connected only through a high impedance.
Second letter:
T All exposed conductive parts are connected via your earth conductors to a local ground connection.
N All exposed conductive parts are connected via your earth conductors to the earth provided by the supplier.
Remaining letter(s):
C Combined neutral and protective earth functions (same conductor).
S Separate neutral and protective earth functions (separate conductors).
TN-C No separate earth conductors anywhere - neutral used as earth throughout supply and installation
TN-S Probably most common, with supplier providing a separate earth conductor back to the substation.
TN-C-S [Protective Multiple Earthing] Supply combines neutral and earth, but they are separated out in the installation.
TT No earth provided by supplier; installation requires own earth rod (common with overhead supply lines).
IT Supply is e.g. portable generator with no earth connection, installation supplies own earth rod.
Inside or nearby your consumer unit (fuse box) will be your main earthing terminal where all the earth conductors from your final sub-circuits and service bonding are joined. This is then connected via the 'earthing conductor' to a real earth somehow...
TN-S The earthing conductor is connected to separate earth provided by the electricity supplier. This is most commonly done by having an earthing clamp connected to the sheath of the supply cable.
TN-C-S The earthing conductor is connected to the supplier's neutral. This shows up as the earthing conductor going onto the connection block with the neutral conductor of the supplier's meter tails. Often you will see a label warning about "Protective Multiple Earthing Installation - Do Not Interfere with Earth Connections" but this is not always present.
TT The earthing conductor goes to (one or more) earth rods, one of them possibly via an old Voltage Operated ELCB (which are no longer used on new supplies).
There are probably other arrangements for these systems too. Also, a system may have been converted, e.g. an old TT system might have been converted to TN-S or TN-C-S but the old earth rod was not disconnected.

 

[amberleaf]

Consumer Units
Live parts must be contained inside enclosures or behind barriers providing a degree of protection of at least IX2X or IPXXB. 416.2.1
The horizontal top surface of a readily Accessible barrier or enclosure must provide a degree of protection of at least IX4X or IPXXD. 416.2.2
All installations must be divided into separate circuits so as to comply with the following :
- avoid danger and inconvenience if a fault develops
- allow safe maintenance, inspection & testing
- prevent any danger that may be caused by the loss of supply to a single circuit e.g. a lighting circuit
- reduce the possibility of nuisance tripping of RCDs by equipment with high cpc currents produced in normal use e.g. computers
- prevent electromagnetic interference between items of electrical equipment
- prevent the accidental energising of an isolated circuit .
314.1

A double pole main switch or linked circuit breaker must be installed as close as possible to the incoming supply at the origin of the installation. 537.1.4
Unless specifically labelled or suitably identified, all 13A socket outlets must be 30ma RCD protected. 411.3.3
Fire detection circuits must be supplied independently of other circuits and not protected by an RCD protecting multiple circuits. 560.7.1
Fire detection .cables, not including metal screened fire resistant cables, must be adequately segregated from cables supplying other circuits. 560.7.7
Extra Low Voltage circuits should not be run in the same wiring system as 230v circuits unless all ELV cables and conductors are insulated for 230v or separated by an earthed metal screen. 528.1
All electrical equipment must be accessible for operation, inspection & testing , maintenance and repair. 132.12
Before an installation or an addition / alteration to an installation is energised, inspection and testing must be carried out to ensure the requirements of BS-7671 have been met and an appropriate Certificate must then be issued. 134.2.1, 610.6, 631.1
Any defects found in the existing installation must be recorded on the Electrical Installation Certificate or Minor Electrical Installation Works Certificate. 633.2
A single pole fuse or circuit breaker must be used with the line conductor only. 132.14.1
Only a linked circuit breaker that breaks all related line conductors can be used with an earthed natural conductor. 132.14.2
All final circuits must be connected to a separate way in the consumer unit. 314.4
In a ccu the natural conductors and cpc's should be connected to their respective terminals in the same order as the phase conductors are connected to the mcb's. 514.1.2

An unfused spur may be connected to the origin of a radial or ring final circuit in the consumer unit. 433.1
All protective devices must be labelled. 514.8.1
A periodic inspection notice must be fixed on or next to the ccu. 514.12.1
Where applicable an RCD notice must be fixed on or next to the ccu. 514.12.2
Where the installation contains wiring colours to two versions of BS-7671 a warning notice must be fixed on or next to the ccu. 514.14.1
A voltage warning notice is only required where a nominal voltage exceeding 230v exists. 514.10.1
A durable copy of the schedule from the electrical installation certificate must be fixed next to or placed inside the consumer unit. In addition to circuit details the schedule must also contain information about the protective measures used in the installation ie automatic disconnection of supply, electrical separation , SELV , RCD. 132.13, 514.9
All literature supplied with fire detection equipment must be made available to the occupant of the dwelling. 560.7.12
Fuses and mcb's must have a breaking capacity greater than or equal to the maximum PFC at the point where the device is installed. 432.1 A lower breaking capacity is allowed if another fuse or mcb with the necessary breaking capacity is installed on the supply side and the energy let-through of both devices will not damage the fuse or mcb on the load side. 434.5.1, 536.1
Consumer units must be spaced at least 150mm away from gas pipes unless there is a pane of non combustible insulating material separating them. OSG p18
In areas subject to flooding, consumer units should preferably be installed above flood water level. OSG p161
Overcurrent protection devices must comply with one or more of the following standards :

Bs 88-2.2 .
Bs 88-6 .
Bs 646 .
Bs 1361 .
Bs 1362 .
Bs 3036 .
Bs en 60898-1 & -2 .
Bs en 60947-2 & -3 .
Bs en 60947-4-1, -6-1 & -6-2 .
Bs en 61009-1 .
533.1

MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE : p-335 / 336

GUIDANCEFOR RECIPIENTS (to be appended to the Certificate)
This Certificate has been issued to confirm that the electrical installation work to which it relates has been
designed, constructed and inspected and tested in accordance with British Standard 7671, (the IEE Wiring
Regulations). You should have received in ‘original’ Certificate and the contractor should have retained
duplicate. If you were the person ordering the work, but not the owner of the installation, you should
pass this Certificate, or copy of it, to the owner.
A separate Certificate should have been received for each existing circuit on which minor works have been
carried out. This Certificate is not appropriate if you requested the contractor to undertake more extensive
installation work., for which you should have received an Electrical installation Certificate.
The Certificate should be retained in safe place and be shown to any person inspecting or undertaking
further work on the electrical installation in the future. If you later vacate the property, this Certificate
will demonstrate to the new owner that the minor electrical installation work carried out complied with
the requirements of British Standard 7671 at the time the Certificate was issued.

MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE :
(REQUIREMENTS FOR ELECTRICAL INSTALLATIONS - BS 767 ( IEE WIRING REGULATIONS )
To be used only for minor electrical work which does not include the provision of new circuit

Agreed limitations on the inspection and testing ← with Client ,

Declaration
I/We certify that the electrical installation work, as detailed in part 1 of this certificate, do not impair the safety of the existing installation, that the said works have been
designed, constructed, inspected and tested in +accordance with BS 7671:2008 * ( IEE Wiring Regulations), amended to the date shown* and that to the best of my/our
knowledge and belief, the time of my/our inspection, complied with BS 7671 except as detailed in Part 1 of this certificate.
This form is based on the model shown in Appendix 6 of BS 7671: 2008

239- Inspection Testing & Certification of Electrical Installations Exam : Part B scenario :
Solution to terminating the underground SWA supply cable :
-&-'s question may lead you to terminate the SWA of the underground supply cable, since the question informs you. "You are NOT allowed to use the supply companies earthing system as a means of earthing the outhouse" However -&-'s mention nothing about earthing the supply cable itself. It is difficult to decide whether -&-'s are just testing the candidates knowledge of this situation VERY thoroughly or alternatively offering a red-herring to mislead the unwary candidate. Whichever is the reason for this question, it caused many exam candidates a great deal of difficulty and lost time trying to decide what the solution was.

The actual solution stems from BS 7671 regulation 542.1.8 part of this reg states , ←

"If the protective conductor ( i.e. the swa ) forms part of a cable, the protective conductor shall be earthed only in the installation containing the associated protective device" This therefore has to be the main house end. See the only possible solution below :
( Main house CCU / TN-C-S / Systems ) MET : ←←

part B scenario : gave many candidates a difficult time. Here you were presented with a TN-C-S system installed in a domestic property, and an underground supply cable is being used to supply an external outhouse. However the electricity supply company will not allow you to use their means of earthing for the outhouse. So how do you provide a means of earthing for the outhouse? Where do you earth the supply cable? What checks must you make on the underground supply cable? Why can't you use the main house TN-C-S system as a means of earthing the outhouse ?

 

[amberleaf]

Many candidates continue to get the value of Zs wrong for the circuit in question in part B of the exam.
A common error when completing questions involving schedule of test results is to forget to indicate functional tests have been performed and found satisfactory/unsatisfactory. To tick the tick box when completing details of ring final circuits, ensuring to indicate continuity of ring final conductors have been performed.
Failure to record the type of earthing system, i.e. TN-S, TN-C-S, TT,
Failure to record the value of Ze, PFC, Nominal voltage, Nominal frequency, are common errors.
Test procedures
A very common question is to explain in detail how to perform an insulation resistance test, often on a lighting circuit. Candidates regularly fail to state the instrument used which is an 'Insulation Resistance Ohm-meter' (Not a Megger! You will not gain any marks if you answer a Megger) Many candidates fail to identify the test voltage required for typical 230/240 volt installation which is 500 volts and the acceptable test value which is 0.5 Meg-ohm or greater (again due to change under 17th edition to a minimum acceptable value of 1.0 Meg-ohm) City and Guilds usually deliberately pick a lighting circuit that is stipulated as having two way switching, just to see if the candidate mentions to test the strappers in BOTH positions.
Failure to mention testing the insulation resistance of both strappers will lose you marks. Be warned!
Candidates regularly make mistakes when answering RCD questions. Often the question or specifications usually given in part B will make reference to a specific type of RCD for example a 30 mA RCD. Candidates are then asked to state the actual test current applicable to test this type of RCD. Candidates regularly incorrectly state the answer as x1/2 x1 and x5 instead of x1/2 = 15mA x1 = 30mA and x5 = 150mA

'Memorandum of Guidance on the Electricity at Work Regulations 1989'
This may help you somewhere on your 2391 ,

5. General :

1. The majority of the regulations are directed at hardware requirements. Installations are required to be of proper construction; conductors must be insulated or other precautions taken; there must be means of cutting off the power and means for electrical isolation. The hardware requirements are complemented by a group of regulations stating principles of safe working practice. Regulation 14, which covers live working, is of particular importance.
2. The scope of the EAW Regulations is limited by the definition of danger and injury solely to risks arising from an electrical source and does not include, for example, control-system faults and consequent hazards such as aberrant machinery behavior.
3. The EAW Regulations revoke a number of specific regulations, but a number remain which either overlap or appear to overlap, for example
1. the Electricity Safety, Quality and Continuity Regulations 2002 (as amended): see the introduction to the Memorandum of guidance.
2. the Low Voltage Electrical Equipment (Safety) Regulations 1988 (made under the Consumer Protection Act 1987);
3. the Building (Scotland) Regulations 2004: these give deemed to satisfy status to BS7671 Requirement for Electrical Installations (also known as the Institution of Electrical Engineers Wiring Regulations, 16 th Edition); and
4. the Cinematographic (Safety) Regulations, 1955.
If demarcation between these sets of regulations and the EAW Regulations is unclear in a particular case, then details should be passed to HSE, via the Enforcement Liaison Officer.
4. Appendices 1 and 2 of the Memorandum of guidance list publications relating to electrical safety.

6. Enforcement
1. There is no expectation that inspectors should change their general approach to enforcement. However, particular attention should be paid to the enforcement of reg 14. (Work on, or near, live conductors).
2. In situations where the 1908 Regulations previously applied or where HSW Act was used, inspectors should now enforce the EAW Regulations.
3. There should be no difference in enforcement between situations in which no specific regulations previously applied and those which were regulated
4. Nothing is required by the EAW Regulations which is not already the norm in the best undertakings.
5. The EAW Regulations will apply to electrical work in domestic premises. Such work will fall to HSE to enforce.
6. Expert assistance to prove the presence of electricity should not be necessary when contemplating enforcement action. Circumstantial evidence should suffice to indicate that electricity is present and that the EAW Regulations apply. Such evidence could include:
1. that the equipment carried a plate indicating that it worked at mains voltage;
2. that the equipment was connected to a supply via a 3-pin plug;
3. that the premises were supplied with electricity for lighting which was working; and
4. that a person on the premises paid an electricity bill.
In court, an expert witness should be able to use such evidence to express a professional opinion as to the dangers which were present or likely to occur.
7. It may also be possible to use an on-site electrician to measure voltages and use his or her measurements in evidence.
8. An improvement notice may be appropriate it conductors are inadequately protected against damage; for example, not routed through conduit, tubing or armouring in premises where the risk of physical damage is apparent. In particularly arduous conditions, e.g. construction work, stronger action may be considered.
9. Exposed and accessible live conductors or a lack of earthing could justify a prohibition notice. Lack of earthing can only be proved by measurement; simple observation is never adequate.

7. Interpretation (Reg 2)
1. The definitions of danger and injury are linked but distinguished to accommodate those circumstances when persons must work on or so near live equipment that there is a risk of injury, ie where danger is present and cannot be prevented.
2. Danger includes danger to the public.
3. The definition of electrical equipment excludes items which only generate electricity adventitiously, eg as static.
4. Earthing and isolation are defined in regs.8 and 12 respectively.
8. Duties (Reg 3)
1. Regulation 3 imposes duties only on employers, employees, the self-employed, and mine or quarry managers. In other cases HSW Act ss.3 and 4 will apply.
2. All duties are limited by the phrase "to matters which are within his control", apart from reg.3(2)(a) which is similar to HSW Act, s.7(b). Some large industries tend to produce written rules which clearly define the extent of an individual's control but it will often be the case that there is overlapping liability where several individuals and/or bodies corporate are duty holders.

9. Systems, work activities and protective equipment (Reg 4)
1. Regulation 4 acts as a catch-all requirement.
2. Due to the broad definition of system (reg 2), reg 4 covers almost every conceivable electrical danger: from an exploding lithium battery in a calculator to the output side of a power station.
3. Systems in vehicles are covered by reg 4, but note should be taken of reg 32 in relation to ships, aircraft and hovercraft.
4. Regulation 4(3) embraces all work which could lead to electrical danger, although such work may not be associated with an electrical system. This would include work in the vicinity of electrical equipment and insulated or uninsulated conductors. The requirement does not limit proximity to conductors, live or dead, but rather regulates the work activity so as not to give rise to danger.
5. Regulation 4(3) is almost always applicable to work on or near underground cables, in which situations the standards of the Construction (GP) Regulations, reg 44 should be maintained, viz electrical isolation by disconnection and secure separation from sources of electrical supply. However, reg 14 should be used if there has been a failure to switch off the supply to such cables before undertaking work. That said, the circumstances of each case will dictate which regulation should be used.
6. The duties in reg 4(4) are not qualified by "so far as is reasonably practicable' and link with reg 14(c) ensuring that protective equipment provided is always suitable for the purpose.
10. Strength and capability of electrical equipment (Reg 5)
1. The assigned rating of electrical equipment represents the extent to which it may be used in an assessment of the adequacy of equipment strength and capability in foreseeable conditions of actual use; but may not necessarily represent all factors to be considered. A technical judgement by a competent person will often be needed to determine adequacy.
2. If a failure has occurred it may be relatively easy to prove a contravention. However, expert support will be required except where a deficiency is obvious and requires no technical proof.

 

[amberleaf]

11. Adverse or hazardous environments (Reg 6)
1. Regulation 6 addresses extrinsic effects which are reasonably foreseeable. For example, in order to prove a contravention of reg.6, it is not necessary to show that electrical equipment is or has been exposed to a flammable atmosphere, but only that it is foreseeable that it could be so exposed.
2. The Memorandum of guidance gives general advice on the different hazardous environments covered by reg 6, and makes reference to relevant standards and publications.
12. Insulation, protection and placing of conductors (Reg 8)
1. This regulation is an example of where the EAW Regulations extend protection to anyone exposed to electrical danger from electrical equipment, including those not at work
13. Earthing and other suitable precautions (Reg 8)
1. This regulation applies to any conductor and not just to metal. It also allows other suitable means of preventing danger as an alternative to earthing.
2. The duty to prevent danger arising is activated only when a relevant conductor becomes charged.
3. Regulation 4 requires that systems are constructed so as to prevent danger; but in the event that danger arises because a conductor which should be earthed is not, reg.8 also becomes relevant.
4. As regards adequate earthing, the use of a conductor with a small cross-sectional area, which is not capable of carrying a heavy current for the duration of the fault, is not acceptable.
5. Inspectors should continue to press for the use of reduced voltage lighting and power tools, e.g. 110v centre tapped to earth in the working environments described in para 19 of the Memorandum of Guidance (e.g. construction work).

14. Integrity of reference conductors (Reg 9)
1. Regulation 9 is fully explained in the Memorandum of guidance.
15. Connections (Reg 10)
1. The definition of danger means that connections have to be mechanically and electrically suitable to prevent the risk of electrical injury.
16. Means for protecting from excess current (Reg 11)
1. The due-diligence defence in reg 29 is important when enforcing this requirement because, in theory, it is impossible in an absolute sense to prevent danger arising before any excess current protection device operates.
17. Means of cutting off the supply and for isolation (Reg 12)
1. This regulation cannot be used to require means to prevent non-electrical hazards arising from the use of electrical controlled systems.
2. Permit-to-work systems relying on a warning notice may be encountered. Where such systems are well established, tried and tested they could represent adequate isolation. However, they need to meet the minimum requirements of this regulation and when assessing such systems, inspectors should seek expert assistance, where appropriate.
3. Regulation 12 covers electrical equipment which may become charged by means other than connection to the supply, e.g. through capacitance or induced current arising from proximity to other live conductors.
4. There are no voltage limits.
18. Precautions for work on equipment made dead (Reg 13)
1. Regulation 13 may apply during any work, be it electrical or non-electrical.

19. Work on or near live conductors (Reg 14)
1. This regulation is very important and should be used to reduce the incidence of live working and to ensure strict precautions are adhered to when such work is carried out.
2. All 3 conditions stipulated in the regulation must be met before live working is permitted.
3. "Reasonable in all the circumstances" (reg 14(b)) means that all necessary precautions must be taken to ensure it is reasonable for someone to be asked to work.
4. Regulation 14(c) could imply that in the absence of injury no precautions can be required in advance. This would mean that notices requiring such precautions could not be issued. This interpretation is not correct because:
1. it would not be reasonable to work in a situation where the necessary precautions had not been taken; and
2. in order to take precautions it is necessary to foresee the potential harm, and such precautions will only be suitable if they are adequate to prevent the harm foreseen.
Therefore, if an inspector judges that the precautions taken will not prevent injury, he or she could issue a notice citing an apparent breach of reg 14.
5. Inspectors should question all live working wherever they find it. This could be in many establishments and also where peripatetic electricians are working.
6. The issue of accompaniment during live work is touched upon in the Memorandum of guidance. The presence of a colleague who could render assistance if safe to do so could prevent injury or mitigate its extent.
20. Working space, access and lighting (Reg 15)
1. This regulation only applies to the period during which work is being carried out.
2. It can be used to prevent the storage of goods etc in front of switchboards on the basis that the act of operating switching device is considered to constitute work on the equipment in question.

21. Competence to prevent danger and injury (Reg 16)
1. If competence is in doubt, inspectors should enquire into:
1. technical knowledge, and
2. experience
in relation to the work activity being undertaken. Clearly, more knowledge is required of those involved in high voltage work compared to those doing 25-volt test work.
2. HSE specialist support is available for assessing electrical competence (via the ELO).
3. The regulation does not require authorisation of competent persons but in conjunction with regs 4 and 14 such authorisation may be required, when necessary, to avoid danger.
4. The regulation does not specify any age limitations. The key requirements are adequate and relevant knowledge and experience, or an appropriate degree of supervision to allow persons to work safely and possibly to acquire those attributes.
22. Defence (Reg 29)
1. The defence only becomes relevant once it has been established that an offence has been committed. It should not affect the judgement of the duty holder as to the steps he or she should take to meet an absolute requirement
2. Employers may suggest that they have taken reasonable steps to meet their obligations by the delegation of responsibility to adequately qualified and instructed staff. This approach is pre-empted by the specific duties placed upon employers and others by reg 3.
3. HSE electrical specialists may be able to provide technical support in relation to a due diligence defence.

23. Exemptions (Reg 30)
1. Any applications for an exemption should be forwarded, together with a full report, to the Local Authority Unit.
24. Disapplication of duties (Reg 32)
1. The EAW Regulations apply to all vehicles, except those exempted by this regulation
2. Sea-going ships are exempt in relation to normal shipboard activities under the direction of the Master, whether they are in dock or under way in an inland waterway or at sea.
3. The term sea-going is not defined in these or any other health and safety regulations, but the intended meaning is clear and common to other regulations (eg Docks, COSHH).
4. The reference to any person in reg 32(b) includes the employer.

Appendix
Key issues on which the EAW Regulations And Electricity (Factories Act) Special Regulations 1908 And 1944 (Plus Exemptions) differ
1. Appendix 3 of the Memorandum of guidance gives information on reg 17 of the old regulations in relation to the new provisions. The minimum dimensions for switchboard passage-ways are given tacit approval.
2. Regulation 14 of the EAW Regulations covers all live working not just work on switchboards above 650 volts.
3. There is no specific requirement under the EAW Regulations for the display-of an electric shock placard or an abstract of the 1908/1944 Regulations. Occupiers should be told to remove abstracts but advised to retain placards where these are appropriate (see page 32, para 23 of Memorandum). There is no objection to occupiers displaying the new regulations in placard form if they desire.
4. There are no voltage bandings in the EAW Regulations.
5. There are differences in definitions between old and new. In particular conductor and danger have different meanings in the EAW Regulations.
6. Regulation 5 of the EAW Regulations corresponds to reg 1 of 1908 but is confined to the prevention of electrical danger. It does not cover machine malfunctions from electrical faults. All at risk are covered by reg 5, not just employees.
7. Under reg 6 of the EAW Regulations (as opposed to reg 27 of 1908) it is no longer necessary to show that equipment is or has been exposed to a flammable atmosphere. A foreseeable exposure will suffice.
8. Regulation 8 of the EAW Regulations applies to all conductors, unlike reg 21 of 1908 which only applied to exposed metalwork.
9. Regulation 13 of 1908 required the earthing of mobile generators. Under the EAW Regulations, reg 8 permits alternative approaches where earthing is not practicable.
10. The EAW Regulations contain no specific requirement for the written authorisation of competent persons, although authorisation may be required when necessary to avoid danger.

 

[amberleaf]

Electrical Safety and you : ( HSE )
INTRODUCTION :
Electricity can kill. Each year about 1000 accidents at work involving electric shock
or burns are reported to the Health and Safety Executive (HSE). Around 30 of
these are fatal. Most of these fatalities arise from contact with overhead or
underground power cables.
Even non-fatal shocks can cause severe and permanent injury. Shocks from faulty
equipment may lead to falls from ladders, scaffolds or other work platforms.
Those using electricity may not be the only ones at risk: poor electrical
installations and faulty electrical appliances can lead to fires which may also cause
death or injury to others. Most of these accidents can be avoided by careful
planning and straightforward precautions.
This leaflet outlines basic measures to help you control the risks from your use of
electricity at work. More detailed guidance for particular industries or subjects is
listed on pages 6 - 8. If in doubt about safety matters or your legal responsibilities,
contact your local inspector of health and safety. The telephone number of your
local HSE office will be in the phone book under Health and Safety Executive. For
premises inspected by local authorities the contact point is likely to be the
environmental health department at your local council.
WHAT ARE THE HAZARDS ?
The main hazards are:
■ contact with live parts causing shock and burns (normal mains voltage,
230 volts AC, can kill);
■ faults which could cause fires;
■ fire or explosion where electricity could be the source of ignition in a
potentially flammable or explosive atmosphere, e.g. in a spray paint booth.
ASSESSING THE RISK :
Hazard means anything which can cause harm. Risk is the chance, great or small, that someone will actually be harmed by the hazard.
The first stage in controlling risk is to carry out a risk assessment in order to
identify what needs to be done. (This is a legal requirement for all risks at work.)
When carrying out a risk assessment:
■ identify the hazards;
■ decide who might be harmed, and how;
■ evaluate the risks arising from the hazards and decide whether existing
precautions are adequate or more should be taken;
■ if you have five or more employees, record any significant findings;
■ review your assessment from time to time and revise it if necessary.
The risk of injury from electricity is strongly linked to where and how it is used.
The risks are greatest in harsh conditions, for example:
■ in wet surroundings - unsuitable equipment can easily become live and
can make its surroundings live;
■ out of doors - equipment may not only become wet but may be at
greater risk of damage;
■ in cramped spaces with a lot of earthed metalwork, such as inside a tank
or bin - if an electrical fault developed it could be very difficult to avoid
a shock.
Some items of equipment can also involve greater risk than others. Extension
leads are particularly liable to damage - to their plugs and sockets, to their
electrical connections, and to the cable itself. Other flexible leads, particularly
those connected to equipment which is moved a great deal, can suffer from
similar problems.

REDUCING THE RISK
Once you have completed the risk assessment, you can use your findings to
reduce unacceptable risks from the electrical equipment in your place of work.
There are many things you can do to achieve this; here are some.
Ensure that the electrical installation is safe
■ install new electrical systems to a suitable standard, e.g. BS 7671 Requirements
for electrical installations, and then maintain them in a safe condition;
■ existing installations should also be properly maintained;
■ provide enough socket-outlets - overloading socket-outlets by using
adaptors can cause fires.
Provide safe and suitable equipment
■ choose equipment that is suitable for its working environment;
■ electrical risks can sometimes be eliminated by using air, hydraulic or hand powered
tools. These are especially useful in harsh conditions;
■ ensure that equipment is safe when supplied and then maintain it in a safe
condition;
■ provide an accessible and clearly identified switch near each fixed machine
to cut off power in an emergency;
■ for portable equipment, use socket-outlets which are close by so that
equipment can be easily disconnected in an emergency;
■ the ends of flexible cables should always have the outer sheath of the cable
firmly clamped to stop the wires (particularly the earth) pulling out of the
terminals;
■ replace damaged sections of cable completely;
■ use proper connectors or cable couplers to join lengths of cable. Do not
use strip connector blocks covered in insulating tape;
■ some types of equipment are double insulated. These are often marked with
a ‘double-square’ symbol . The supply leads have only two wires - live
(brown) and neutral (blue). Make sure they are properly connected if the
plug is not a moulded-on type;
■ protect light bulbs and other equipment which could easily be damaged in
use. There is a risk of electric shock if they are broken;
■ electrical equipment used in flammable/explosive atmospheres should be
designed to stop it from causing ignition. You may need specialist advice.
Reduce the voltage
One of the best ways of reducing the risk of injury when using electrical equipment
is to limit the supply voltage to the lowest needed to get the job done, such as:
■ temporary lighting can be run at lower voltages, eg 12, 25, 50 or 110 volts;
■ where electrically powered tools are used, battery operated are safest;
■ portable tools are readily available which are designed to be run from a
110 volts centre-tapped-to-earth supply.
Provide a safety device
If equipment operating at 230 volts or higher is used, an RCD (residual current
device) can provide additional safety. An RCD is a device which detects some, but
not all, faults in the electrical system and rapidly switches off the supply. The best
place for an RCD is built into the main switchboard or the socket-outlet, as this
means that the supply cables are permanently protected. If this is not possible a
plug incorporating an RCD, or a plug-in RCD adaptor, can also provide additional safety.

RCDs for protecting people have a rated tripping current (sensitivity) of not more
than 30 milliamps (mA). Remember:
■ an RCD is a valuable safety device, never bypass it;
■ if the RCD trips, it is a sign there is a fault. Check the system before using it
again;
■ if the RCD trips frequently and no fault can be found in the system, consult
the manufacturer of the RCD;
■ the RCD has a test button to check that its mechanism is free and
functioning. Use this regularly.
Carry out preventative maintenance
All electrical equipment and installations should be maintained to prevent danger.
It is strongly recommended that this includes an appropriate system of visual
inspection and, where necessary, testing. By concentrating on a simple, inexpensive
system of looking for visible signs of damage or faults, most of the electrical risks
can be controlled. This will need to be backed up by testing as necessary.
It is recommended that fixed installations are inspected and tested periodically by
a competent person.
The frequency of inspections and any necessary testing will depend on the type of
equipment, how often it is used, and the environment in which it is used. Records
of the results of inspection and testing can be useful in assessing the effectiveness
of the system.
Equipment users can help by reporting any damage or defects they find.
Work safely
Make sure that people who are working with electricity are competent to do the
job. Even simple tasks such as wiring a plug can lead to danger - ensure that people
know what they are doing before they start.
Check that:
■ suspect or faulty equipment is taken out of use, labelled ‘DO NOT USE’ and
kept secure until examined by a competent person;
■ where possible, tools and power socket-outlets are switched off before
plugging in or unplugging;
■ equipment is switched off and/or unplugged before cleaning or making
adjustments.
More complicated tasks, such as equipment repairs or alterations to an electrical
installation, should only be tackled by people with a knowledge of the risks and the
precautions needed.
You must not allow work on or near exposed live parts of equipment unless it is
absolutely unavoidable and suitable precautions have been taken to prevent injury,
both to the workers and to anyone else who may be in the area.
Underground power cables
Always assume cables will be present when digging in the street, pavement or near
buildings. Use up-to-date service plans, cable avoidance tools and safe digging
practice to avoid danger. Service plans should be available from regional electricity
companies, local authorities, highways authorities, etc.
Overhead power lines
When working near overhead lines, it may be possible to have them switched off if the owners are given enough notice. If this cannot be done, consult the owners

about the safe working distance from the cables. Remember that electricity can
flash over from overhead lines even though plant and equipment do not touch
them. Over half of the fatal electrical accidents each year are caused by contact
with overhead lines.

Mac : can you put the ( HSE ) stuff in the Doc , Useful Information for Apprentices , please Sorry about that . Amberleaf

 

[amberleaf]

Definitions : Earth Fault Current :
A Fault Current which flows to Earth ,

Earth Fault Loop Impedance :
The Impedance of the Earth Fault Current Loop starting and ending at the point of the Earth Fault .
This Impedance is denoted by ( Zs )
The Earth Fault Loop comprises the following , starting at the point of Fault :
* the Circuit Protective Conductor ,
* the Consumers Earthing terminal and Earthing Conductor ,
* for TN-Systems , the return path ,
* for TT and IT Systems , the Earth return path ,
* the path through the Earthed Neutral point of the Supply Transformer and the Transformer Winding ,
* the Phase Conductor from the Transformer Supply to the point of Fault ,

BS 7671:2008
(i) The Electrical Installation Certificate required by part 6 : should be made out and signed or otherwise
authenticated by a competent person or persons in respect of the design, construction, inspection and testing of the work

(ii) The Minor Works Certificate required by Part 6 : should be made out and signed or otherwise authenticated by
a competent person in respect of the design, construction, inspection and testing of the minor work.
(iii) The Periodic Inspection Report required by part 6 : should be made out and signed or otherwise authenticated
by a competent person in respect of the inspection and testing of an installation
(iv) Competent persons will, as appropriate to their function under (i) (ii) and (iii) above, have a sound
knowledge and experience relevant to the nature of the work undertaken and to the technical standards set
down in these Regulations, be fully versed in the inspection and testing procedures contained in these
Regulations and employ adequate testing equipment
(v) Electrical Installation Certificates will indicate the responsibility for design, construction, inspection and
testing, whether in relation to new work or further work on an existing installation .
Where design, construction, inspection and testing are the responsibility of one person a Certificate with a
single signature declaration in the form shown below may replace the multiple signatures section of the model form

FOR DESIGN, CONSTRUCTION, INSPECTION & TESTING
I being the person responsible for the Design, Construction, Inspection & Testing of the electrical
installation (as indicated by my signature below), particulars of which are described above, having
exercised reasonable skill and care when carrying out the Design, Construction, Inspection & Testing,
hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge
and belief in accordance with BS 7671 :2008, amended to .............(date) except for the departures, if
any, detailed as follows.
(vi) A Minor Works Certificate will indicate the responsibility for design, construction, inspection and testing of
the work described on the certificate.
(vii) A Periodic Inspection Report will indicate the responsibility for the inspection and testing of an installation
within the extent and limitations specified on the report.
(viii) A Schedule of Inspections and a Schedule of Test Results as required by part 6: should be issued with the
associated Electrical Installation Certificate or Periodic Inspection Report.
(ix) When making out and signing a form on behalf of a company or other business entity, individuals should
state for whom they are acting.
(x) Additional forms may be required as clarification, if needed by ordinary persons, or in expansion, for larger
or more complex installations.
(xi) The IEE Guidance Note 3 provides further information on inspection and testing on completion and for
periodic inspections ,
ELECTRICAL INSTALLATION CERTIFICATES NOTES FOR FORMS 1 AND 2
1. The Electrical Installation Certificate is to be used only for the initial certification of a new installation or
for an addition or alteration to an existing installation where new circuits have been introduced.
It is not to be used for a Periodic Inspection, for which a Periodic Inspection Report form should be used.
For an addition or alteration which does not extend to the introduction of new circuits, a Minor Electrical
Installation Works Certificate may be used.
The "original" Certificate is to be given to the person ordering the work (Regulation 632.1 A duplicate
should be retained by the contractor.
2. This Certificate is only valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test
Results.
3. The signatures appended are those of the persons authorized by the companies executing the work of
design, construction, inspection and testing respectively. A signatory authorized to certify more than
one category of work should sign in each of the appropriate places.
4. The time interval recommended before the first periodic inspection must be inserted (see IEE Guidance
Note 3 for guidance).
5. The page numbers for each of the Schedules of Test Results should be indicated, together with the total
number of sheets involved.
6. The maximum prospective fault current recorded should be the greater of either the short-circuit current or
the earth fault current.
7. The proposed date for the next inspection should take into consideration the frequency and quality of
maintenance that the installation can reasonably be expected to receive during its intended life, and the
period should be agreed between the designer, installer and other relevant parties