cpc sizing

[Guest123]

Slight aside, what do you folk generally do if wiring in singles say conductors at 2.5mm, do you wire cpc as 2.5mm or smaller. I tend to use 2.5mm throughout.

Always size for size when using singles for me too.:shuriken:

 

[Chr!s]

The main issue comes down to temperature, when designing a circuit you would check that the live conductors are protected as per chapter 43 using the adiabatic in 434.5.2, where the protective conductor is of the same csa then this adiabatic will also ensure the protective conductor is adequate.

Where we have a reduce csa we need to us the adiabatic in chapter 54 543.1.3.

What we are looking for is to ensure the limiting temperatures are not exceeded by the reduced csa.

Regards Chris

 

[i=p/u]

this also is for disconnection times not exceeding 5 seconds, so high can the temperature get withing 5 seconds chris..? is there a graph/table tells you current =heat??? im just wondering here so mighting be correct question

 

[ackbarthestar]

I bet there ain't many sparks that know that, or have ever done that or ever will do that.

I think they (T&E) comply with BS 6004 which is the exception to the rule, as copper was in short supply after the 2nd ww.
The general rule, BS7671, for final circuits under 16mm2, the cpc is the same size as the live conductors. Table 54.7 introduces the use of smaller cpcs in relation to the live conductors that will give an acceptable adiabatic effect under fault conditions.

 

[malcolmsanford]

The use of the adiabatic as our learned friend IQ states is down to cost.

Very rarely in smaller circuits would you bother with runing 2.5mm singles and a 1mm CPC as it is not worth it unless your doing thousands of these circuits, the norm is CPC same size as the LIVES.

The real benefit comes with larger cables and large runs. If you had a 95mm 3phase + N run of 200mtrs then it would be well worth doing the calculation to see if you could in fact run a 35mm CPC as that is a good cost saver.

The same as you would also do calculate the chance of an 1/2 neutral, but I noticed that the new regs have included Triplen Harmonics and so the 1/2 neutral days maybe numbered.

 

[Knobhead]

I noticed that the new regs have included Triplen Harmonics and so the 1/2 neutral days maybe numbered.

It’s now possible to get super size neutral 4 core cable to handle the harmonic currents. I wonder about all the 3½ core cables I’ve put in? some must be cooking by now.

 

[Knobhead]

One of the main problems is the lack of monitoring on the neutral. The phase conductors are protected, while the neutral is unhappily frying it’s self and the rest of the cable.