A good guide For 'exported PME' and outbuildings!

[IQ Electrical]

For anyone bored by the constant myths and rumours regarding this subject, have a read of this guide from the IEE on supplies to detached outbuildings.

It was published in 2005 but the important bits remain unchanged and might be of some help!

 

[WayneL]

It always baffles me why the outbuilding PME handwringers only seem to apply their logic to sheds and garages....it never seems to occur to them that the same perceived hazards presumably will apply to external lights and sockets connected to the PME earth on the main building.

This is true - the old 'outside tap' is another that springs to mind - when it's run straight through the wall yet bonded inside the house to a PME supply

 

[malcolmsanford]

Strange enough wayne one of the reasons a lot of the older sparks still baulk at the export of the PME was that oulined of the outside water pipe.

In the old Electricity Supply Regulations 1988 which was succeeded by the ESQCR-2008, the old ESC-1988 had a PME section and it recommended that an outside water pipe that was supplied from a pipe through the wall/ground from inside the house should be sleeved.

I suppose old habits die hard with some.

 

[amberleaf]

Sorryabout this Dan / Jason . don’t know where to drop it .

Wordsof Wisdom . Why ?? do I need a Fire Alarm

FireAlarm Systems is used to ProtectLife & Property . Therefore ! Any Company or Person who Owns something of Value has a Valid Interestin installing a Fire Alarm . “ LIFE ! ◄◄

•AccentLighting . Lighting used to Emphasise an Object or Specific Area(s) .

•“Meaning “ Ampere Squared Seconds ( I2 t ) The measurement of HeatEnergy developed within a circuit duringthe fuse’s clearing . It can be Expressed as “ Melting ( I2 t ) or “ Racing ( I2 t ) or the sum of them as “Clearing ( I2 t ) “ ( I )stands foreffective let-through current ( r.m.s. ) Which is squared . & the ( t )stands for time of Operating in seconds.

•PowerLoss ( Cable ) Loss caused by internal cable Impedance . mainly ( I2 R ) Theloss cause heating .

•Continuity: The state of being Whole . – Unbroken .

•Drawing: Block diagram . Asimplified drawing of a system showing major items as blocks . normally used toshow how the system works & the relationship between major items . • Drawing : line Schematic ( diagram) Shows how a circuit works . • Drawing: Plot or Layout . Shows the “ Floor Plan “ . • Drawing: Wiring diagram . Shows how the devices are Interconnected .

 

[amberleaf]

•Impedance(A) Theopposition to current flow in an A.C. circuit ; Impedance includes Résistance (R ) Capacitive Reactance ( X C L ) itis measured in Ohms .

•Inverter : Anitem that changes D.C to A.C.

•Kirchhoff’s Law : (1) The algebraic sum of the currents atany point in a circuit is Zero . (2) The algebraic sum of the product of the current & the impedancein each conductor in a circuit is Equal to the electromotive force in thecircuit .

•Load : (1) Adevice that receives power . (2) The power delivered to such a device . - Load Factor . The ratioof the average to the Peak load over a period . Start with the Basic . - Magnet : A body that produces a magnetic field externalto itself . magnets attract iron particles . -Magnet Field : (1)A magnetic field is said to exist at the point at which a force over &above any electrostatic force is exerted on a moving charge at that point . (2)The force field established by A.C.through a conductor – especially a coiled conductor . -Magnet : Thoseportions of the magnet towards which the external magnetic induction appears toconverge ( South ) or diverge ( North ) - Motor : An apparatus to convert from Electrical to Mechanicalenergy . -Motor Capacitor: A single-phaseinduction motor wit an auxiliary starting windings connected in Series with acondenser for better starting characteristics . - Power Factor : Correctioncoefficient for A.C. power necessary because of changing current & voltagevalues . - Efficiency : The ratio of the Output to theInput . - Electromagnet : A deviceconsisting of a ferromagnetic core & a coil that produces appreciablemagnetic effects only . when an Electric current exists in the coil . - Electromotive force ( emf ) Voltage

 

[amberleaf]

Electricalforce that causes current ( freeelectrons ) to flow or move in an electrical circuit . This unit ofmeasurement is the Volt . - Self-Inductance : Magneticfield induced in the conductor carrying the current . * Electron : The subatomic particle that carriesthe Unit Negative charge of electricity . * Proton :Thehydrogen atom nucleus . it is Electrically positive . - Manufactures’ Conditions: Criteria set forth by materials vendorwithin which they will honour Warranties . - Polyphase Circuits : Circuits running onA.C. & having two or more interrelated voltages . Usually of Equal amplitudes. Phase differences . & periods . etc . if a Neutral conductor exists . Thevoltages referenced to the Neutral conductor are Equal in amplitude & Phase. The common version is that of Three-phase , Equal in amplitude . with Phases( 120º apart ) - Powerapparent :The product of r.m.s.volts times r.m.s.amperes . - Rated : Indicating the Limitsof Operating characteristics for application under specified conditions . - Reactance : (1)The imaginary part of Impedance . (2)The opposition to A.C. to capacitance ( Xc) & Inductance ( XL) - Reactor : A device tointroduce Capacitive or Inductive reactance into a circuit . - Résistance : The opposition in a conductor tocurrent . The real part of Impedance . - Short Circuit : Anoften-Unintended Low résistance path through which current flows around .rather than through . a component or circuit .

 

[amberleaf]

You willget this on Drawings . Apprentices . - Service Cable : The service conductors made up in the form ofa cable . - Service Conductors : Thesupply conductors that extend from the Street Main or Transformers to theService equipment of the premises being supplied .

-Surge : (1)A sudden increase in voltage & current (2) Transient condition . - Starter : An electric controller for accelerating amotor from Rest to NormalSpeed & for stopping the motor . - Starting Winding :Winding in an electric motor used only during the brief period when the motoris starting .

DoNot mix up the twoWords . - Stator/ Starter . ◄◄ - Stator :The portion of a rotating machine that includes & supports the stationary ActiveParts . * Volt :The practical unit of voltage of electromotive force . One volt sends a currentof One ampere through a résistance of One ohm . * Voltage: Voltage is the force . pressure . or electromotive force ( emf ) that causes electriccurrent to flow in an electric circuit . its unit of measurement is the Volt .which represents the amount of electrical pressure that causes current to flowat the rate of One Ampere through a résistance of One ohm . Voltage in anelectric circuit is often considered similar to Water pressure in a pipe orwater system . * Voltage Drop( Vd ) The voltage drop in an electrical circuit is difference between thevoltage at the power source & the voltage at the point at which electricityis to be used The voltage drop ( Loss ) is created by the résistance of theconnecting conductors . * Watt : Theunit of measurement of electrical power or rate of Work ( 756 Watt ) isequivalent to ( 1 hp ) The Watt represents the rate at which power is expendedwhen a pressure of ( 1V ) causes current to flow at a rate of ( 1A ) in a D.C.circuit or in A.C. circuit at Unity ( 100% ) power factor . The number of Watts equals the pressure ( in Volts ) multiplied by thecurrent ( in Amperes )

 

[IQ Electrical]

I think the above was meant for a different thread?

 

[amberleaf]

IQ ELECRRICAL .



Sorry about that . the builder chap who’s working next door to me . has be using a mini digger ?? needless to say he took out some Cables .Internet . I’ve had trouble with the internet . & getting in to the Forum sorry about the scattering on the download . do except my apologies .Amber

 

[IQ Electrical]

IQ ELECRRICAL .



Sorry about that . the builder chap who’s working next door to me . has be using a mini digger ?? needless to say he took out some Cables .Internet . I’ve had trouble with the internet . & getting in to the Forum sorry about the scattering on the download . do except my apologies .Amber

Beware man with digger!

 

[TinyT]

TN-S supply. 6mm swa, 3core, via a 32a MCB from house, to pool plant room outhouse.
There is a gas pipe in the room that is copper but is run in plastic before it comes in. At the moment i have bonded the pipe with a 10mm earth conductor to the CU MET in the outhouse. Is this acceptable??? I know it is a little of topic

 

[oldAL]

Hi all, Im new here and joined as I found this forum when searching for some stuff,
I think something very important has been missed out here,
TNCS is NOT the same as PME,
and its not statutory to be as of this time, so no matter what the DNO state they dont have to comply with a TNCS=PME at this time.

AL.

 

[IQ Electrical]

TNCS is NOT the same as PME,
and its not statutory to be as of this time, so no matter what the DNO state they dont have to comply with a TNCS=PME at this time.

AL.

I agree that not all TN-C-S is PME however the vast majority is in the UK with the exception of a comparatively rare PNB however there is still a PEN conductor.

I've also read the piece of your post that I've quoted above and can't really understand the point you're making?

 

[oldAL]

for a tncs to be PME it is required to be rodded at regular intervals along its length, and also to have a rod as close as is reasonably practicable to the consumers installation, most TNCS in the UK do NOT comply with this requirement, hence they are not proper PME supplies.
I assume this is what you are getting at?
a lot of people mistakenly mix up tncs and pme as being the same supply method, its not,
pme must in its nature be tncs, but tncs does not always have to be multiple earthed.

Al.

 

[malcolmsanford]

The Chances are that the Gas pipe in the plant room is not an extraneous conductive Part and may therefore not need bonding back to the MET.

 

[TinyT]

The Chances are that the Gas pipe in the plant room is not an extraneous conductive Part and may therefore not need bonding back to the MET.

That's what i thought. I have still strapped a 10mm g/y to it though, no harm in that is there?
The supply cable is fed via a 100ma RCD in the house, im moving it off though because other circuits on the RCD side have faults. No harm in having an swa distribution circuit protected by an MCB only is there?

 

[malcolmsanford]

That's what i thought. I have still strapped a 10mm g/y to it though, no harm in that is there?
The supply cable is fed via a 100ma RCD in the house, im moving it off though because other circuits on the RCD side have faults. No harm in having an swa distribution circuit protected by an MCB only is there?

You can always check to see if the pipe is an extraneous conductive part, Attach a wander lead to the MET in the house and via your meter to the pipe and do an IR test. If you get above 22Kohms reading then it is not an extraneous conductive part and therefore you do not need to bond it, and as you say the supply pipe is plastic, there is little chance of it being an ECP.

You say your earth system is a TN-S and the 100mA RCD would make me think that it was fitted to the installation perhaps because the Ze might at one time, or still be high. Have you done a Ze to check? If you do remove the distribution cable from the RCD protection you will need to make sure your Zs is low enough to activate the MCB in time.

 

[IQ Electrical]

22 kOhms is the figure, below this and the part is classed as extraneous.

 

[TinyT]

Zs is good. lower than 0.6 if i recall.

 

[Chr!s]

for a tncs to be PME it is required to be rodded at regular intervals along its length, and also to have a rod as close as is reasonably practicable to the consumers installation, most TNCS in the UK do NOT comply with this requirement, hence they are not proper PME supplies.

I Disagree

I assume this is what you are getting at?
a lot of people mistakenly mix up tncs and pme as being the same supply method, its not,
pme must in its nature be tncs, but tncs does not always have to be multiple earthed.

Agreed, PNB being one variation.

Al.

ESQCR

Protective multiple earthing
9.—(1) This regulation applies to distributors' low voltage networks in which the neutral and
protective functions are combined.
(2) In addition to the neutral with earth connection required under regulation 8(3)(b) a distributor
shall ensure that the supply neutral conductor is connected with earth at—
(a) a point no closer to the distributor’s source of voltage (as measured along the distributing
main) than the junction between that distributing main and the service line which is most
remote from the source; and
(b) such other points as may be necessary to prevent, so far as is reasonably practicable, the
risk of danger arising from the supply neutral conductor becoming open circuit.
(3) Paragraph (2)(a) shall only apply where the supply neutral conductor of the service line
referred to in paragraph (2)(a) is connected to the protective conductor of a consumer’s installation.

 

[oldAL]

Like I said,
even ESQCR doesn't describe a proper PME as recognised by most other developed countries in the world,
have you checked the conditions that are required by 2012 for a TNCS to be called PME ?
I think you may find them somewhat more stringent.

 

[Engineer54]

Like I said,
even ESQCR doesn't describe a proper PME as recognised by most other developed countries in the world,
have you checked the conditions that are required by 2012 for a TNCS to be called PME ?
I think you may find them somewhat more stringent.

You will find that most, if not all new DNO supplies are meeting PME conditions.

Then you have the god knows how many old supply cables, that were previously TN-S but now being converted to PME because of there lead sheath's deterioration etc. There are many such cables, that are in the process of being converted, but do not yet meet full PME conditions. I suppose you could call these situation TNC-S supplies!!! ....Conversion costs money, so it's not going to all happen over night so to speak, but all i'm sure, all will eventually meet PME conditions, just maybe later rather than sooner ...lol!!! .

 

[Chr!s]

Like I said,
even ESQCR doesn't describe a proper PME as recognised by most other developed countries in the world,
have you checked the conditions that are required by 2012 for a TNCS to be called PME ?
I think you may find them somewhat more stringent.

ESQCR is statutory in this country. That is what the law requires.

What other countries do is irrelevant.

IEC 60364-1 which most developed countries base many standards on also describe TNC-S PME in the same way.

What recognised stanard are you referring to ?

Regards Chris

 

[Silly Sausage]

Does anyone know of a decent book for electricity distribution, from generation up to consumers installations, that would explain PME etc etc in a not too analytical way?

It could help with my insomnia...

 

[Chr!s]

Does anyone know of a decent book for electricity distribution, from generation up to consumers installations, that would explain PME etc etc in a not too analytical way?

It could help with my insomnia...

I have a Earthing guide which is not to analytic, other than that try:

"Transmission and Distribution Electrical Engineering"

 

[Silly Sausage]

Thanks...but I might have to take out a second mortgage!
Transmission and Distribution Electrical Engineering: Amazon.co.uk: Colin Bayliss, Brian Hardy: Books

 

[Chr!s]

Archy

Try this link :http://www.eon-uk.com/distribution/...nts/CN East/East Earthing Manual Feb 2002.pdf

Chris

 

[Silly Sausage]

Cheers Chris,

Had a quick scan through, that'll keep me going for a while.
File saved.

Andy

 

[bozobro0]

So i take it this means then that a house that used to be TT but has been upgraded to TNC-S which has a seperate wc in the yard,which some still have,that has a lighting circuit and a cold water feed that normaly comes from the ground has to be seperate from the house, has to have a seperate means of earthing-TT.

 

[SW1970]

This is one of the most interesting threads on the forum!

Here's a variation on a theme. TN-C-S house, twin and earth with small earth conductor to detached garage with no earth rod. What if extraneous-conductive-part is not actually in the garage but is for example, a water pipe on the outside wall of garage (which does not appear inside the garage at all and there are no other e-c-parts inside the garage). Does the need for improved earthing still apply in this scenario? I'm thinking the answer might be yes because user could (e.g.) have a tool plugged into extension lead running into garage. Tool develops fault, and user touches water pipe.

Thanks, SW

 

[IQ Electrical]

This is one of the most interesting threads on the forum!

Here's a variation on a theme. TN-C-S house, twin and earth with small earth conductor to detached garage with no earth rod. What if extraneous-conductive-part is not actually in the garage but is for example, a water pipe on the outside wall of garage (which does not appear inside the garage at all and there are no other e-c-parts inside the garage). Does the need for improved earthing still apply in this scenario? I'm thinking the answer might be yes because user could (e.g.) have a tool plugged into extension lead running into garage. Tool develops fault, and user touches water pipe.

Thanks, SW

The point here is that the pipe wouldn't be classed as an extraneous-conductive part because it wouldn't be capable of introducing a different potential into the equipotential zone.

Because the person using the tool in your scenario would actually be standing on 'true earth' bonding the external pipe to the PME earth terminal would create a greater danger, this is why it was common practice to insert an insulating section in the pipework to external taps on PME installations.