This discussion is locked.

You cannot post a reply to this discussion. If you have a question start a new discussion

Thoughts on 3M max tails protection with SPD & isolator in tails?

DNO allowance for tails protection from their fuse is commonly 3M. - 3M is deemed AFAICT to extent through any in-line isolator, whether or not that isolator is property of DNO or is consumer fitted part. (The latter is not spelled out by DNO SSEPD who just state the 3M tails figure without further qualification).
If said isolator begins to sprout additional complexity such as MCB and SPD as a shunt addition, my interpretation (Definitions, part 2) is that it still doesn’t yet qualify as a consumer unit, hence the 3M rule could be said to still run straight through it as far as the farthest CU.

- Any thoughts?

0 justinneedham over 4 years ago

I think we all agree, thanks for the little discussion.

For MHRestorations: The 3M is stated in a fairly unqualified way (and there can be no real qualification possible, since,as has been pointed out, it is not part of BS7671). The key point of my post was to avoid upsetting DNO and/or ending up with any sort of business culpability by overstretching their ruling (in whatever way that may be possible). See "New connections guide Part 2"
https://www.ssen.co.uk/connections/usefuldocuments/
Cancel
Vote Up 0 Vote Down

Cancel
0 Alan Capon over 4 years ago

Sparkingchip:

So we can use the DNO main fuse to protect up to three metres of meter tails.

But presumably that is from the actual fuse, so includes the tails into the suppliers meter as well as the tails out to the consumer unit. . .

Not quite. The distance is measured from the outgoing (load) terminals of the meter, or the outgoing terminals of the isolator where this has been provided by the supplier.

Regards,

Alan.
Cancel
Vote Up 0 Vote Down

Cancel

Thoughts on 3M max tails protection with SPD & isolator in tails?

Join us to get the best from IET EngX.

Community Rules & Guidelines