Splitting meter tails at 3m

[davesparks]

Doesn't that Wylex switch fuse have double terminals on the main switch that you can loop from?

The older ones did, but I think that one looks like the more recent version with the single terminal.

 

[brianmoooore]

The older ones did, but I think that one looks like the more recent version with the single terminal.

Don't think the switch is right for the later version. Looks like a 160CM to me, which should have the loop terminals. A look behind the grey terminal cover will confirm.

 

[pc1966]

There isn't a 3m tails limit in BS7671, to the best of my knowledge, it's a rule that DNOs have and I don't imagine you'd be wildly exceeding it.

The 3m limit is mentioned under 433.2.2(ii) and under 434.2.1(i) in the context of where OCPD is located (at source or CSA reduction of cable run, or further along it).

However, the specific aspect of relying on the DNO fuse for that OCPD is under 434.3(iv) where it is permitted provided the DNO ("distributor" in the text) agrees to its use.

So if the DNO said yes, then the cable is protected at source and no 3m limit, however, if they have not approved that and/or the fuse is not able to protect according to BS7671 (5s disconnection time for sub-main fault) then you would need to put in your own protection that does meet BS7671.

The DNO is not obliged to meet the BS7671 disconnection times as their fuse is intended to protect their network from overload (and as a means of isolation, of course) and it is not for shock protection ADS, hence the reason that Ze can be up to 0.8 ohm TN-S and still seen as OK even for a 100A fuse supply that would need 0.3 ohm or so to be compliant for ADS.

 

[timhoward]

The 3m limit is mentioned under 433.2.2(ii) and under 434.2.1(i) in the context of where OCPD is located (at source or CSA reduction of cable run, or further along it).

Agreed, I was aware of these regs, but I think this easily causes confusion. These are our 3m rules about moving the OCPD along a circuit. I think of these regs when I think of bus-bar chambers and a short run in a smaller conductor in mechanically protected containment to a switched fuse.
The thing is, these regs only come into play if the supplier fuse isn't deemed to protect the tails.

However, the specific aspect of relying on the DNO fuse for that OCPD is under 434.3(iv) where it is permitted provided the DNO ("distributor" in the text) agrees to its use.

Ah yes, I should read the complete post before starting to reply to it! This is the bit I'd emphasise!

In the OP's case it seems as though it could be arranged to have minimal extra tails length. Not one I'd lose sleep over, compared to some we see!

 

[pc1966]

Agreed, here the tails seem to be well protected in the plastic pipe along with their usual double sheath. Extending/splitting them to another fused-switch along side it would seem a reasonable thing to do.