size of tails

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mikel

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I have been asked to quoe to replace a consumer unit with a new one. When I went to look at job I found that the flat has two consumer units fitted (wylex rewirable jobbies) one of which controls an economy 7 heating (storage heaters) and hot water immersion heater. the incoming supply is fed from a 100amp supply to a henley block where the tails are split to two different meters. From these meters tails go to each consumer unit. The 'normal unit' is fed by 25mm tails the economy 7 unit has 16mm tails. As i plan to renew the tails do I need to upgrade the tails to the economy 7 unit to 25mm. Hope this makes sense. I can't find anything in the 'wiring regs' but the on site guide says that meter tails should be 25 mm

 
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Mikel

On consumer unit changes I tend to upgrade tails as a matter of course. If it is a 60 amp Henley block I would upgrade this to 100 amp too. If main fuse has 100 amp on it it is likely to be 100 amp. This is what I do although many sparks probably would say eco7 will never overload 16 mm tails.

Batty

 

Admin1

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Not really, Mine is brand new and says 100 A on the front of it. But it is actull 80 A, because WPD are too tight to give out 100 A's.

:D

 
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Have you been asked to replace the "economy 7 heating (storage heaters) and hot water immersion heater" supply..

or just the main Property CU?

If haven't been asked then leave as is..

maybe note it down on cert & inform customer?

Some old wylex boxes are a bit of a swine to get 25mm into??

so don't commit to doing something that is a pain in the butt! :) ;)

 
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If main fuse has 100 amp on it it is likely to be 100 amp
Not really, Mine is brand new and says 100 A on the front of it. But it is actull 80 A, because WPD are too tight to give out 100 A's. :D
I would concur with that Admin! ;)

You do have the difference between an adhesive label stuck around the fuse carrier with the rating on it..

and the embossed working on the side of the carrier

IMO if it is a label stuck on..

that is quite probably the rating in side ..

if it is the original embossed wording ..

this is just the max possible rating.. that could be in there

Not the actual rating! :)

 

Admin1

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Mine's embossed on the front, down here, because we are posh. :p

 
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In my area all new main fuses are grey henley ones. The lower amperage ones have 60/80 amps on the side but I am sure they are the same carriers as the 100 amp ones.

Batty

 
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I would guess that about 90% of fuse carriers that I have looked at and are marked up as 100A have either a 60A or 80A fuse..... I think that the rating of the meter (especially mechanical ones) gives a better indication of the supply fuse.

 
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Indeed so Noz! ;)

We did have a 100a fuse at our house..

but when e-on recently changed the meter they swapped out for a 80a! :_|

original carrier still has the posh embossed writing (bit like admins:x),,

but they stuck a big white label round the front of it saying 80a fitted!

He said it was standard practice now to downgrade the average domestic property to 80a? ?:| ? :|

 

mikel

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Been asked to replace both, as they are very diffcult to get to and they want them more accessible. Economy 7 one has one 20A and one 15A fuse in it. Just confused a little with on site guide saying they had to be 25 mm when I can't find that in regs

 
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16mm tails will be adequate. The 25 mm tails is for main consumer unit. This is what electric boards specify as minimum tail size. I had a new install a few years ago for a portacabin. supply was only 40 amps but electric board would not connect up because I had used 16mm tails into a garage supply unit.

Batty

 
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Been asked to replace both, as they are very diffcult to get to and they want them more accessible. Economy 7 one has one 20A and one 15A fuse in it. Just confused a little with on site guide saying they had to be 25 mm when I can't find that in regs
It doesn't say directly in the reg's you should have 25mm tails..

But on one of the relevant tables in Appendix 4 will tell you that 16mm cables are too small for 100amp..

The OSG makes an assumption that the MAX demand will be up to 100A..

the typical rating of your bog-standard CU main switch..

the old wylex board probably has a mains switch rated 80A or 60A?

IMO Its just a matter of providing for a worse case loading..

as you are quoting for both boards.. the cost of a couple of tails isn't going to break the job...

If I was doing it I would build in the costs & swap the lot! ;) :)

then have a Guiness Drink:^O

 

steptoe

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Been asked to replace both, as they are very diffcult to get to and they want them more accessible. Economy 7 one has one 20A and one 15A fuse in it. Just confused a little with on site guide saying they had to be 25 mm when I can't find that in regs
dont worry about either,(neither is law), in all honesty you cant verify the size of the fuse anyway, cos you are not LEGALLY allowed to pull the fuse to look at it never mind cut any seal that might be on it,

just put NOT VERIFIED in the box and mark it as a 'requires investigation' .

16mm tails are more than enough,

unless its the dreaded PME/TNCS, then you need to confirm with the DNO as to their requirements.

 

steptoe

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If you are changing the tails anyway, the price difference between 16mm and 25mm isn't much!
totally agree,

but there is NO requirement to change them.

and if they are terminated into the meter then there is also no way of changing them legally without opening the meter seal and re terminating. ]:) ] :)

 

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