Discuss Bit of fun, Interpret the previous reg in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Lister1987

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I fancy a bit of fun, but in a way to benefit us all. The idea is simple; A reg number is posted and the next poster has to give their interpretation of the reg AND what they believe the regs intent to be.

From a trainee, it may be hard to truly understand why a reg is worded the way it is and what it's intent is, so I figured let's see how we, as a forum, can aid it.

Example:
Poster 1: 110.1

Poster 2: The regulation is.... and I believe it's intent to be . . - Next reg; 433.1.1

And so the game goes on, it'll be interesting to read, hopefully enough get involved ?

To start this off: 131.1.1

GO!
 
TL;DR
A game to share and build on interpretation of individual regs
I fancy a bit of fun, but in a way to benefit us all. The idea is simple; A reg number is posted and the next poster has to give their interpretation of the reg AND what they believe the regs intent to be.

From a trainee, it may be hard to truly understand why a reg is worded the way it is and what it's intent is, so I figured let's see how we, as a forum, can aid it.

Example:
Poster 1: 110.1

Poster 2: The regulation is.... and I believe it's intent to be . . - Next reg; 433.1.1

And so the game goes on, it'll be interesting to read, hopefully enough get involved ?

To start this off: 131.1.1

GO!
that's shocking.
 
only 1 reg. required "job done, pay now"
 
It is a good idea I am sure some suggestions will get some debate.
 
To start;
131.1.1. no such reg in the book
following on;
434.5 Characteristics of a fault current protective device
Every fault current protective device shall meet the requirements of this regulation
 
434.5.1 Except where the following paragraph applies, the rated short-circuit breaking capacity of each
device shall be not less than the maximum prospective fault current at the point at which the device is installed.
A lower breaking capacity is permitted if another protective device or devices having the necessary rated shortcircuit
breaking capacity is installed on the supply side. In this situation, the characteristics of the devices shall be
co-ordinated so that the energy let-through of these devices does not exceed that which can be withstood, without
damage, by the device(s) on the load side.
NOTE: Technical data for the selection of protective devices can be requested from the manufacturer.
434.5.2 A fault occurring at any point in a circuit shall be interrupted within a time such that the fault current
does not cause the permitted limiting temperature of any conductor or cable to be exceeded.
For a fault of very short duration (less than 0.1 sec), for current limiting devices k2S2 shall be greater than the value
of let-through energy (I2t) quoted for the Class of protective device to BS EN 60898-1, BS EN 60898-2 or BS EN
61009-1, or as quoted by the manufacturer.
The time, t, in which a given fault current will raise the live conductors from the highest permissible temperature in
normal duty to the limiting temperature, can, as an approximation, be calculated from the formula:
where:
t is the duration in seconds
S is the cross-sectional area of conductor in mm2
I is the effective fault current, in amperes, expressed for AC as the rms value, due account being taken of the
current limiting effect of the circuit impedances
k is a factor taking account of the resistivity, temperature coefficient and heat capacity of the conductor
material, and the appropriate initial and final temperatures. For common materials, the values of k are
shown in Table 43.1.
 
I fancy a bit of fun, but in a way to benefit us all. The idea is simple; A reg number is posted and the next poster has to give their interpretation of the reg AND what they believe the regs intent to be.

From a trainee, it may be hard to truly understand why a reg is worded the way it is and what it's intent is, so I figured let's see how we, as a forum, can aid it.

Example:
Poster 1: 110.1

Poster 2: The regulation is.... and I believe it's intent to be . . - Next reg; 433.1.1

And so the game goes on, it'll be interesting to read, hopefully enough get involved ?

To start this off: 131.1.1

GO!
Excellent suggestion. Has the potential to be a truly educational tool for electricians. Hope it takes off.
 
434.5.1.

I'll have a go and try and explain this for trainees.

In the event of an overload scenario (as opposed to a high current short duration fault such as a short circuit), we understand that a device can be reset and will operate within it's design parameters because typically the fault is less than the rated breaking capacity of the device. Considering a typical BS EN 60898 circuit breaker, the rated breaking capacity is 6000A.

Interrupting any fault current under this, SHOULD mean the device will suffer no damage and can be returned to active service. Clearly interrupting say a 40A overload on a 32A device should present no problem and the device should continue to meet it's design specification for a considerable period of time. Sure there may, if there is repeated tripping under such an overload, be slight contact degradation that can result in a high resistance contact and ultimately device failure, but overall the device should be fine.

Now consider short duration high current faults, say line to earth (on a TNCS or TNS system) or line to neutral short circuits.

With good earthing, it's easy to achieve prospective fault currents in these situations of over 1000A. Clearly breaking a fault of this magnitude is an entirely different kettle of fish. If the installation is very close to the substation or is three phase (or both), it's entirely possible to have situations where the prospective fault is over 6000A.

When a protective device tries to break a fault current that is larger than it's rated breaking capacity various things can happen....

In the case of a fuse, the fuse element could break and then if the fuse itself doesn't meet specification, it could continue to arc internally, ultimately resulting in an explosion of hot plasma and molten metal. This is why high rupture capacity (HRC) fuses are filled with special sand... to extinguish the arc.

In the case of a circuit breaker, it could explode or suffer internal damage (that may not be visible to the user). The internal damage may mean it no longer operates within parameters, if it operates at all, or it may result in a more catastrophic failure if it were to be closed on a fault.

@pc1966 posted a video about devices being tested within their specifications but which failed... badly... if you've not watched it, go and do so because it's a good primer on why you should never just re-energise a tripped breaker (Another video on fuses versus MCCB - https://www.electriciansforums.net/threads/another-video-on-fuses-versus-mccb.193572).

So... this regulation formalises this requirement by specifically stating the short circuit breaking capacity of protective devices must be larger than the prospective fault current. Providing the devices comply with this requirement, you should in the case of a circuit breaker at least be able to reset them and leave them in service. If it's found that the prospective fault current is larger than the breaking capacity of a device, the device should be replaced at your earliest convenience with one that has the required capacity.

Now, someone can have a punt at 433.1.204
 
Now, someone can have a punt at 433.1.204
Go on then.
433.1.204
Accessories to BS1363 may be supplied through a ring final circuit, with or without unfused spurs protected by a 30A or 32A protective device [ BS88 fuse / MCB / RCBO meeting relevant regs ]
The circuit shall be wired with copper conductors having line and neutral conductions with a minimum cross sectional area of 2.5mm sq. except for two-core mineral insulated cables complying with BS EN 6072-1 for which the minimum cross sectional area is 1.5 mm sq. Such circuits are deemed to meet the requirements of 433.1.1 if the current carrying capacity (Iz) of the cable is not less than 20A and if, under the intended conditions of use the load current in any part of the circuit is unlikely to exceed for long periods the current carrying capacity (Iz) of the cable.


This describes the good 'ole British ring final circuit and explains several things.
In certain circumstances you can do something which would normally not be allowed - you can use a 30/32A OCPD with 2.5mm T+E cable. As the best possible current carrying capacity is only 27 amps (clipped direct, table 4D5) and this is less than 30/32A it does not meet reg 433.1.1. However the exemption is permitted if certain conditions are met:
  • obviously it must be wired in a ring, allowing the load current to be balanced on the two legs.
  • the circuit must supply 13 amp sockets / plugs / fused connection units (BS 1363 accessories)
  • the tabulated current carrying capacity in table 4D5 for the method of installation needs to be at least 20 amps. Methods 101 and 103 do not meet this requirement, so a cable over a plasterboard ceiling in >100mm thick insulation or a cable floating inside an insulated stud wall shouldn't be used as part of a ring final circuit.
  • the load current at any point in the ring (and spurs if any) shouldn't be expected to exceed the current carrying capacity of the cable used for long periods of time.

[1.5mm mineral insulated cable can be used too, refer to table 4G1A]
Improvements on this attempt welcome!

I'll throw up 411.1 for next punter.
 
Go on then.
433.1.204
Accessories to BS1363 may be supplied through a ring final circuit, with or without unfused spurs protected by a 30A or 32A protective device [ BS88 fuse / MCB / RCBO meeting relevant regs ]
The circuit shall be wired with copper conductors having line and neutral conductions with a minimum cross sectional area of 2.5mm sq. except for two-core mineral insulated cables complying with BS EN 6072-1 for which the minimum cross sectional area is 1.5 mm sq. Such circuits are deemed to meet the requirements of 433.1.1 if the current carrying capacity (Iz) of the cable is not less than 20A and if, under the intended conditions of use the load current in any part of the circuit is unlikely to exceed for long periods the current carrying capacity (Iz) of the cable.


This describes the good 'ole British ring final circuit and explains several things.
In certain circumstances you can do something which would normally not be allowed - you can use a 30/32A OCPD with 2.5mm T+E cable. As the best possible current carrying capacity is only 27 amps (clipped direct, table 4D5) and this is less than 30/32A it does not meet reg 433.1.1. However the exemption is permitted if certain conditions are met:
  • obviously it must be wired in a ring, allowing the load current to be balanced on the two legs.
  • the circuit must supply 13 amp sockets / plugs / fused connection units (BS 1363 accessories)
  • the tabulated current carrying capacity in table 4D5 for the method of installation needs to be at least 20 amps. Methods 101 and 103 do not meet this requirement, so a cable over a plasterboard ceiling in >100mm thick insulation or a cable floating inside an insulated stud wall shouldn't be used as part of a ring final circuit.
  • the load current at any point in the ring (and spurs if any) shouldn't be expected to exceed the current carrying capacity of the cable used for long periods of time.

[1.5mm mineral insulated cable can be used too, refer to table 4G1A]
Improvements on this attempt welcome!

I'll throw up 411.1 for next punter.

I'll just add my usual comment about this regulation... this is the only regulation that defines a what a ring final circuit can be. Based on your comments, it's acceptable to change up the cable size when running in insulation. I did one rewire where there was insulation present, so based on installation methods I upped the cable size for the segments running through insulation.

And for this one, I'm going to put my tin hat on... based on that definition of a ring final, you could in theory run a spur to more than one accessory providing the cable used was suitably sized. Whilst this is not outlined in Appendix 15, which many consider to be the de facto list of what you can and can't do with a ring circuit... if for example you spurred off a ring with 6mm (without looking at the BBB I'm reluctant to say 4mm) you could supply two double socket outlets... the cable itself would meet the requirements (installation methods aside) and whilst you could in theory connect four 13A loads to it, if you did that with any ring final circuit you would expect it to trip the breaker anyway, but the cable itself would be fine. However, this has the potential to raise all sorts of issues if someone adds to that segment thinking it's a radial... but then I would hope when they isolated to do the works they would realise. Good practice says it shouldn't be done, but the regulations don't explicitly say you can't do it. Hence the lollipop circuit is allowed.
 

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