Meter Tails

I'm replacing two fuse boxes by one CU.

There are 16 mmsq tails from supply to meter - from meter to Henley block - from block to fuse boxes.

Do I really have to use 25mmsq tails from Henley block to my new CU?

Other than (possibly) satisfying regs - I can't see it makes any sense.

(The new meter was installed in the last 10 months - fitter didn't change any of the tails)

Reply to
Peter Ramm
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What is the rating of the main supply fuse? What is the total length of tails from the meter to the consumer unit, via the block? What sort of earthing do you have? What size are the earthing conductors?

Christian.

Reply to
Christian McArdle

It depends (a) on the assessed maximum demand via your new CU and (b) on the size of the distributors main fuse.

(a) For 6181Y single-sheathed tails in free air the rating is 87 A for

16 mm^2 and 114 A for 25 mm^2.

(b) If you use 16 mm^2 tails and the main fuse is 100 A you will need to show by calculation (using the adiabatic equation) that the tails are protected by the fuse in the event of a s/c fault in your CU. To avoid the need for calculation use 25 mm^2 tails. If the main fuse is 60 or

80 A this does not apply.

HTH

Reply to
Andy Wade

100Amp About 18 inches Earth from incoming cable shield 16mmsq
Reply to
Peter Ramm

Yes - thanks - but my point is that any current which passes from my new CU to Henley block in a failure is already passing through 16mmsq so anything I use of greater area and less resistance in series cannot improve the situation. What am I still missing here?

Reply to
Peter Ramm

Personally, I would replace the tails with 25mm. It would take 2 minutes. I did so with mine and I only have a 60A fuse.

Christian.

Reply to
Christian McArdle

Sorry, I read your first post in a hurry and didn't take that in - just assumed is was 25mm^2 from the meter to the service connector block. Nevertheless, new work should comply with current regulations and that means using 25mm^2 tails throughout unless the assessed MD is 87 A or less and there's no diversity applied at the CU (i.e. sum of MCB ratings in the CU is also

Reply to
Andy Wade

Yep that's basically the approach I've taken, I could seen no reason to not replace 'my' tails with 25mm^2 when I replaced the CU, I may try and get the Dist co. to replace theirs as well.

Reply to
chris French

I'd upgrade the tails to the new CU and call the Leccy Co. to come and upgrade their bit as well. With the new requirements now, they shouldn't have a problem doing that for you, and for nowt'.

Reply to
BigWallop

Well, by having a length of 25mmsq at the end rather than the existing

16mmsq you'll be reducing the total impedance of the path from supply mainfuse to a hypothetical short between the tails near your CU and back to the supply point, thereby increasing the fault current and (hopefully) reducing the time for the supply fuse to blow. Yes, it's a marginal effect, but vaguely beneficial - equivalent to shortening the 16mmsq tails, as it were.

That's in addition to the general "25mmsq is the worry-free size to use, and might even encourage the supply co. to upgrade next time one of their finest is Doing Stuff by your meter"...

Stefek

Reply to
Stefek Zaba

I'm going to go ahead with 25mmsq and will then get supply company to upgrade their bits when I've finished everything.

Many thanks to all for explanations/suggestions much appreciated.

Reply to
Peter Ramm

If you were to pull the seals and run the tails all the way back to the meter yourself you probably wouldn't be the first person to do so.

Reply to
Dave

The bit between the meter and the Henley block is all yours, too. You don't need to call the electricity company in to replace that part.

Christian.

Reply to
Christian McArdle

In message , Christian McArdle writes

Yes,so I wonder why they seal the cover on that?

I replaced mine all the way to the meter, the ones twixt Henely block and meter were much older than all the rest, a bit of economising here at some point. Thee insulation was sound but seemed to be some sort of rubber, covered with a cloth/fabric cover of some sort.

Reply to
chris French

Yes it's yours, but you can only replace it if your meter has a separate cover over those terminals, and older meters don't. (Breaking any seals that gain access to the meter inlet and voltage coil terminals could get you into serious trouble.)

Reply to
Andrew Gabriel

Are such meters still in service, though? I'd have thought they'd all been replaced by now.

Christian.

Reply to
Christian McArdle

Of the various premises I have anything to do with, or any of my relations live in, they're all this type. I very rarely see the split terminal cover type. Actually, two relatively new houses up the road from me (couple of years old) had the meter type fitted with only a single connection cover, so use of the split type is not universal in new meters.

Reply to
Andrew Gabriel

Actually, I misread. I thought you meant meters without a separate terminal cover at all (so you have to break the main meter seal to make connections), not ones without separate seals for inlet and outlet.

Christian.

Reply to
Christian McArdle

Our meter still has one cover over all the terminals. I broke that seal anyway as the elec company had already said to break the fuse seals when changing the CU, and you can just as easily steal electricity from there as at the meter so I dont see it matters too much ;o) (apparently our meter was changed 20 years ago and isnt due for replacement for another 15 years I think they said!?)

Reply to
a

I just had a brand new meter (electronic) fitted, and there's a single (sealed) cover over both sets of terminals.

But at least the man resealed the main fuse for me, after I took it out to fit a 100A isolator...

Reply to
Bob Eager

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