ProMbrooke:

I am glad you brought up external Ze varying, as I think this will be an excellent reason to use full size CPCs on circuits up to 16mm2. Sure this would help reduce touch voltage with IMO less copper than local supplemental bonding, but the the argument can be made that the adiabatic method can not be guaranteed as being fully free from hazard.


A Ze of  0.04 ohms could be measured on the public supply and CPCs sized based on a 2 cycle breaker clearing time, however if during a power cut someone was to roll a generator up to the property that Ze could spike to 2.5 ohms whereby a circuit would have a clearing time of 10 seconds. While this time would not present a touch voltage risk in that voltage on the output terminals of the generator would sharply decline, the CPC would be exposed to current far longer than the adiabatic equation assumes possibly exceeding 150*C. Beyond 250*C there is the risk of annealing where the CPC would essentially become compromised thereafter at all terminations and splices. 


 

   

I think you've missed my point about measuring Ze. Very soon, unless someone can come up with a new method, the Ze you measure will mean nothing because of inverters close to the installation on the network.

ProMbrooke:

I am glad you brought up external Ze varying, as I think this will be an excellent reason to use full size CPCs on circuits up to 16mm2. Sure this would help reduce touch voltage with IMO less copper than local supplemental bonding, but the the argument can be made that the adiabatic method can not be guaranteed as being fully free from hazard.


A Ze of  0.04 ohms could be measured on the public supply and CPCs sized based on a 2 cycle breaker clearing time, however if during a power cut someone was to roll a generator up to the property that Ze could spike to 2.5 ohms whereby a circuit would have a clearing time of 10 seconds. While this time would not present a touch voltage risk in that voltage on the output terminals of the generator would sharply decline, the CPC would be exposed to current far longer than the adiabatic equation assumes possibly exceeding 150*C. Beyond 250*C there is the risk of annealing where the CPC would essentially become compromised thereafter at all terminations and splices. 


 

   

I think you've missed my point about measuring Ze. Very soon, unless someone can come up with a new method, the Ze you measure will mean nothing because of inverters close to the installation on the network.