Can you join Main Protective bonding conductor

[Michaelwgroves]

One thing you won't be aware of, all the pipes are cross bonded on the boiler, so I'm not expecting an issue, but gonna test anyway.

 

[Simonslimline]

As has already been mentioned in post 18, how did you carry out the adiabatic for a Main protective bonding conductor?

Is the TN-C-S, PME or PNB?

 

[Michaelwgroves]

As has already been mentioned in post 18, how did you carry out the adiabatic for a Main protective bonding conductor?

Is the TN-C-S, PME or PNB?

Take a look at this thread;

6mm Earth and Main protective bonding conductors - https://www.electriciansforums.co.uk/threads/6mm-earth-and-main-protective-bonding-conductors.123287/

 

[Richard Burns]

As has already been mentioned in post 18, how did you carry out the adiabatic for a Main protective bonding conductor?

Is the TN-C-S, PME or PNB?

The main protective bonding conductor if non TNCS must be >= half the size required for the earthing conductor (and >=6mm²); therefore application of the adiabatic equation to determine the size required for the earthing conductor will define the minimum size for the bonding conductor.
Because a 250A BS1361 fuse at 400V will give a csa of just less than 6mm² in the worst case and any smaller fuse will give a lower csa, as the I²t will be lower, the calculation becomes redundant for most DNO supplies with Uo of 230V and the default 6mm² can be applied without calculation.
PME systems are only dependent on selection from 54.8.

 

[Simonslimline]

The main protective bonding conductor if non TNCS must be >= half the size required for the earthing conductor (and >=6mm²); therefore application of the adiabatic equation to determine the size required for the earthing conductor will define the minimum size for the bonding conductor.
Because a 250A BS1361 fuse at 400V will give a csa of just less than 6mm² in the worst case and any smaller fuse will give a lower csa, as the I²t will be lower, the calculation becomes redundant for most DNO supplies with Uo of 230V and the default 6mm² can be applied without calculation.
PME systems are only dependent on selection from 54.8.

out of interest, what if the supply is Protective neutral bond?

Still TN-C-S but not PME!

Thanks.

 

[Michaelwgroves]

Is the TN-C-S, PME or PNB?

Sorry forgot to answer this question, my installation is PME.

 

[Richard Burns]

out of interest, what if the supply is Protective neutral bond?

Still TN-C-S but not PME!

Thanks.

From my point of view, even though I have not seen this referenced, the purpose of increasing the size of the earthing conductor on a PME system is because the earthing conductor may, in the case of the loss of the external supply neutral, carry the installation load current via the extraneous conductive parts.
In the case of a PNB system the earthing conductor will not carry the installation current if the supply neutral is lost as there is no circuit from the earthing conductor to the transformer star point. Also because of the more limited nature of the neutral conductor there is a lower chance of disconnection even if there happens to be a casual earth path of high resistance. Therefore I believe there is no requirement to apply the increased csa requirements needed where there is a PME supply.