electricalforum.nz

Hi,

Sorry for the long winded explanation but I had a job today that I livened up a new distribution board (non domestic) for testing which had a high earth fault loop test of 43ohms. I tested the distribution board that feed the new board which was 38 ohms. Then tested the MEN board that feed the first distribution board and the reading was down to 0.42ohm. I’ve found the first Distribution Board in the chain had a ‘Main Earth’ connected via a driven electrode. However the switch board had had the MEN Link disconnected. (The board looked about 10-15 years old). This sub-main was protected by a 32amp, 30mA RCD, which is why I’m guessing the MEN link had been disconnected. I know the rules say in Part 2 of 3000 that there needs to be an MEN link if the earth is connected via an earth electrode. But is there anywhere in Part 1 that says this is acceptable (Certified Design), taking into account that the Sub-main that is supplying the first distribution board is protected by RCD at the point of supply? And is there any risk associated with leaving it like this?? Thanks

Short answer: No.

The system as described does not have an acceptable system of protective earthing for either of the 2 DBs and their associated final subcircuits.
Any "Part 1 solution" must always be no less safe than working to Part 2.

It was at one time acceptable to use a PEN submain (c/w N-E link and electrode at the DB) to a DB within the same structure.
It was also acceptable at one time to use RCD protection for fittings (eg lights) added to a final subcircuit that didn't have a PEC
But it has never been acceptable to use RCD instead of having a PEC in the submain.

Thanks AlecK - I thought that was the case, but just double checking to see if there was a clause somewhere that I had not seen. Thanks