new consumer unit 25mm tails

[lobello]

Hello

Had a new consumer unit fitted recently.

At end of day the electrician pointed out the tails from meter to CU were 16mm and the fuse at the supply head may well be 100 amps. We couldn't check this as the supply heads for the flats are in locked room and site manager chap wasn't around. Left it with the sparky that he'd come back and check another time.

Anyways when I googled this subject various stuff came up suggesting that it's obligatory to change the tails to 25mm if not already on a new consumer unit install?

Electrician has suggested swapping supply head fuse for a 60 or 80amp one if it's currently 100amps. Not possible as Managing Agents are adamant fuse cannot be changed.

It's a flat I rent and am keen to have all up to latest regs and specification, covers me insurance wise and are far as possible ensures safety of my tenants. I paid a fair old whack for the new unit install and a few other bits and pieces...

So is swapping 16mm for 25mm tails when changing the consumer unit a law or a regulation or a guideline...?

Is it something that ought to have been covered under the install of the new consumer unit regardless...?

If the fuse at the supply head is currently 60 or 80 amps perhaps all is good and I can forget the 16mm tails, or regardless ought I be getting new tails put in..?

Thanks in advance.

 

[malcolmsanford]

No it is a recommendation that on a CU swop you change the tails to 25mm, but at the end of the day the size of the distributor fuse or in your case the main intake fuse will denote the size of your tails. As this seems to be a flat I would guess that there is little chance you will ever need a fuse larger then 60amp, and would hazard a guess that unless the fuse blew at one time, and the only available was a 100amp jobby in the van, then your fuse will be 60 perhaps 80

I would wait till the electrician can access the main intake before worrying too much, as said I doubt your flat would draw anything near 40 amps at any given time, I'm sure he will sort it out.

 

[lobello]

No it is a recommendation that on a CU swop you change the tails to 25mm, but at the end of the day the size of the distributor fuse or in your case the main intake fuse will denote the size of your tails. As this seems to be a flat I would guess that there is little chance you will ever need a fuse larger then 60amp, and would hazard a guess that unless the fuse blew at one time, and the only available was a 100amp jobby in the van, then your fuse will be 60 perhaps 80

I would wait till the electrician can access the main intake before worrying too much, as said I doubt your flat would draw anything near 40 amps at any given time, I'm sure he will sort it out.

Thanks Malcolm.

Ok understood it's a recommendation. Does beg the question if the Electric Board/DNO could have put a 100 amp fuse in prior (all be it in extremis) what's to stop then doing that at some point in the future and therefore the switching to 25mm tails begins to make sense.

Not sure on the 40 amps as whole flat is electric - immersion storage water tank, convector/storage heater, electric shower, ceramic hob and electric cooker and of course lights and sockets. So yes a flat but quite possibly more demand on the electrics than a house with gas cooker, gas heating and water...

 

[malcolmsanford]

Not sure of your setup regards the flats, but one configuration there will be a main header from the DNO perhaps if it's a large block that will be 3 phase, and from the head will be most likely individual meters to a flat and then a switch fuse for the individual flat, that is the one you need to be checking to make sure of the fuse size. But it could be your meter is in the flat and so the configuration is slightly different

Bottom line the DNO will not upgrade their fuse to 100amp if your tails are 16mm, well they shouldn't put it that way.

 

[Engineer54]

Thanks Malcolm.

Ok understood it's a recommendation. Does beg the question if the Electric Board/DNO could have put a 100 amp fuse in prior (all be it in extremis) what's to stop then doing that at some point in the future and therefore the switching to 25mm tails begins to make sense.

Not sure on the 40 amps as whole flat is electric - immersion storage water tank, convector/storage heater, electric shower, ceramic hob and electric cooker and of course lights and sockets. So yes a flat but quite possibly more demand on the electrics than a house with gas cooker, gas heating and water...

Malcolm is correct, there is little to no chance that all of your connected loads will be operating at the same time, and for any period of time. So 40 to 45A is a pretty good call, as to your actual demand....

 

[lobello]

Thanks again. Set up is

Locked Room on ground floor with supply heads for all flats in block (3 floors and 3 flats on each floor)
Meter outside my front door in communal area on 2nd floor, other flats meters are also outside their doors, CU is above front door inside the flat.

It's the fuse in the locked room the sparky was talking about checking and even swapping, pretty sure that's the DNO's one..

He didn't mention the switch fuse...if it's a matter of getting this fuse changed then all sounds easier and certainly more guaranteed solution. Is said switch fuse likely to be at the meter end of tails i.e. in communal area or at CU end of tails i.e. in my flat...?

 

[telectrix]

generally speaking, the switch fuse should be at the supply end of the tails. or at least within 3meters. this sw.fuse is there solely to protect the tails from an overload/short circuit before the protective devices ( MCBs) in your consumer unit.

 

[jaresquire]

Had my NICEIC annual inspection on the 4th and tail sizes on upgrades were discussed. The view was that outwardley undersized tails were quite acceptable as long as they showed no signs of overheating for the usual system load and that, of course, the CU was within the 3m guideline for downstream protective devices. The inspector gave as an example that 6mm tails to say an additional CU via henley blocks would be acceptable. Not that I would install such tails, but if they are acceptable then they don't have to be changed.

:helmet:

 

[Guitarist]

I think it's unlikely to be a 100A fuse. Plus, as already said, the DNO won't upgrade it from 60A to 100A if 16mm tails are in place.

 

[jaresquire]

Did my sisters CU upgrade a few weeks ago, 2 bed house , 16mm tails and 100A main fuse ( cause it fell out when I touched it)

 

[Octopus]

Out of interst, what does the EIC state the main fuse is?

 

[needasparks]

I think it's unlikely to be a 100A fuse. Plus, as already said, the DNO won't upgrade it from 60A to 100A if 16mm tails are in place.

Got to agree, not very likely its going to be bigger than 60amp if its a block of flats. If its the nomal ryefield layout thats all they fit.

 

[lobello]

Out of interst, what does the EIC state the main fuse is?

"To be verified"...!

 

[somersetsparks]

Size of main fuse is a perfectlty acceptable LIM on an EICR, 16mm tails are O.K even on a 100A fuse in reality in a domestic situation, I wouldn't worry at all. If they are flats, they will more then likely be on 60A fuses in a Ryfield Unit. We usually only fit 80A fuses to all Domestic supplies anyway unless 100A is specificallyu asked for.

 

[Taylortwocities]

Even if you pull the service fuse you may be none the wiser. Often the fuse is riveted in the fuse carrier and there is no way of examining the fuse value. :rolleyes4: