Splitting meter tails at 3m

[sean1990]

I've haven't got a way back to the main supply and need to add a consumer unit for a garage conversion but the tails are on a double pole isolator switch so was going to split the tails at the 60a fused isolator about 2-3m from the main supply is there anything wrong with this or am I just over thinking it

 

[UNG]

Looks like the split con needs terminating properly for starters

Would it be right to assume that the switch fuse pictured is the main point of isolation for the installation and the split con feeds the CU

 

[sean1990]

Am going to reterminate it and move it down and no there's a double pole switch in the meter box for isolation 2-3m away from the switch fuse which is in the garage why I was just going to split tails from here

 

[UNG]

How are the tails installed and what's protecting the 2 - 3m tails up to the switch fuse

 

[sean1990]

The tails run in the cavity wall can't get a rod across

 

[timhoward]

I think the OP is saying he has supplier fuse, isolator, 2 -3 m of tails which appear in the top of his photo.
He wants to split tails there, and run one set of tails down into that switched fuse and connect the splitcon to wherever it's going.
And run another new set of tails to a new CU that's very near.

If I have this right, how near is the new CU?

 

[sean1990]

Basically split the tails feeding the fused switch refeed the fused switch with the splitcon on one set of tails and another set feeding the new consumer unit underneath the fused switch so the henley blocks would be where the fused switch is now

 

[timhoward]

I don't immediately see a problem, the difference between what is there now and what you are proposing doesn't add up to much in real terms. Henley blocks and short extra tails doesn't really change that much.

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.

I was also idly wondering whether there's any desirable way to do this all-in-one enclosure, e.g. I don't know what the fuse rating was protecting the splitcon but wondered if a suitable fuse carrier in your new CU would be available. Or (definitely 2nd choice) a type C MCB if manufacturer tables say selectivity is achieved between it and the highest rated downstream MCB. Just thinking out loud, splitting tails is probably easiest.

 

[sean1990]

Think you've just hit the nail on the head with all in one CU was trying to keep upstairs flat and garage on separate CU for future expansion as he has two other garages attached but it be easier to have all on one and CU thank you

 

[brianmoooore]

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

 

[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.