socket ring to 15A on consumer unit?

[andy1020]

Hi folks, another query you'll likely be able to help me with..

our 2 bed semi has a 20yr old(ish) consumer unit with fuses as opposed to MCBs. The label for each fuse has one of the 30A fuses marked dwnstrs sockets, as expected and another 15A fuse marked immersion heater (again as expected). Turns out though, that the sockets are running off the 15A fuse and the 30A is actually running the cooker.

It's my guess that the cooker was added later (or the electric shower, using the cooker's space) and so the sockets were wired into a now disused immersion heater fuse.

I reckon it's safe to simply put 30A fuse wire into the 16A fuse running the sockets. The wiring will obviously all be up to it and each space in the consumer unit is the same isn't it? simply different fuses? Better still, can you get MCB's designed to fit single blade fuse carriers in old units, or do they only fit new consumer units? or what about a new 30A fuse carrier so that it's marked the correct rating (which I guess keeps things right for anyone else in the future...)

Can anyone second my suspicions - is it common to put sockets onto another circuit on the unit to make space? or have i missed something..
and my solution - simply change the fuse wire?

Thanks, Andy.

 

[davy_owen_88]

I reckon it's safe to simply put 30A fuse wire into the 16A fuse running the sockets. The wiring will obviously all be up to it and each space in the consumer unit is the same isn't it? simply different fuses?

You reckon wrong. If it was running an immersion heater then its most probably a 2.5mm^2 radial. Suitable for a max. of 20A. The wiring might have been totally replaced with a ring circuit but that needs to be verified before upgrading the fuse wire.

A simple rule: Never assume anything when it comes to electrical circuits/wires! Prove that its suitable before you touch it.

Can anyone second my suspicions - is it common to put sockets onto another circuit on the unit to make space? or have i missed something..
and my solution - simply change the fuse wire?

Its likely that when the shower/cooker etc was fitted there was not enough room and instead of getting a larger consumer unit they just moved the circuits onto another fuse. This is very bad practice though. The fuse wires might not be suitable and may well be dangerous.

Do NOT change the fuse wire until you know for sure the cables supplying that circuit are suitable. I would suggest calling in an electrician as it seems someone has altered your wiring without having a clue what they were doing. It might be dangerous or it might just be a simple case of the wrong fuse carriers being used or wrong labels. Either way, get it checked out just to be on the safe side.

Davy

 

[ATES]

Evening Andy,

Simply increasing the fuse rating is potenially one of the dangerous things you do, and can lead to overloading of the circuit cables, overheating, fire, and conductor deterioration. Sorry to scare you, but this is how it is.

i.e are you sure that the sockets are on a ring, and there is end to end continuity of all conductors, if not then 30a is well above the current carrying of 2.5mm cable used for socket circuits!

Unless you are qualified and competent to fully test this circuit i would leave it to a professional.

cheers ant

as the yanks would say, long time listener, first time caller!

 

[ATES]

you beat me davy!

 

[andy1020]

thanks Davy / Ant.
yes, that's why I'm asking abouyt the consumer unit. I'm no spark, but I know what I'm doing up to a poiint, (I'm a physics teacher) and know what happens if you're wire isn't thick enough for the current you're drawing... I'm don't take chances (I'm in support of unqualified not being able to work on electrics, though some of the qualified worry me- like the guy who owned the house before and did this...)

This is very bad practice though. The fuse wires might not be suitable and may well be dangerous.

so do you mean that the wires within the consumer unit itself for that fuse might not be thick enough, or do you just mean the wires for the immersion heater going from the consumer unit (I know these wouldn't be up to the job obviously...)

If the twin & earth for the mains socket ring (which should be fine, though I'll check the diameter when I look at it...) has been connected directly to the consumer unit, (ie neutral to common neutral block and live to fuse, that's right isn't it?)

edited after reading other posts....

so you're saying that the mains might not even be a ring (although it was opriginally on a 30A when the house was built only 20yrs ago, so it should be a ring...?) I'll know if there's 2 sets of wires going into that fuse in the unit, is that right?

Obviously I should check all sockets for continuity too, but I think in a modern house with a 30A fuse originally for the mains ring and a 15A originally for the heater then it must be a ring...?

 

[davy_owen_88]

What I mean is, its possible that the immersion heater was disconnected and a few sockets added from a junction box (fed by the 2.5mm radial). This would then mean you' are at the maximum permissible fuse rating already (15A).

The other point I made is that its possible the previous owner just disconnected the cables from 1 fuse carrier and connected it to another to make space for the shower/cooker (maybe moving the lights circuit onto a 15 or 30A fuse (this would be very dangerous).

The best solution I have is to take the cover off your consumer unit and post a few pictures here and we might be able to tell what is going on. Have a good look at the wires coming into the consumer unit and check that there are never 2 different size wires connected to the same fuse. Also check that the circuit you are thinking about upgrading to 30A has 2x 2.5mm^2 cables going in.

Davy

 

[securespark]

This would then mean you' are at the maximum permissible fuse rating already (15A).

If the circuit is a 2.5 radial (rated around 28A), then you could protect that circuit with a 20A device.

 

[davy_owen_88]

*Edited out due to thick moment*

 

[securespark]

Mods

Please remove my comment here, and Davey's above...

 

[andy1020]

great Davy, thanks.

you've confirmed what i thought- I'll take a look at it. It's a small house so nothing should've been added from the immersion heater cable hopefully... and all lights are on 5A so hopefully not a dangerous bodge, just bad practise to save a new consumer unit...

I'll check for the proper cables running to the fuse.

so can you get something other than fuse wire to fit an old CU ?

Thanks guys.

 

[davy_owen_88]

Wake up, Davey!

You can get 20A 3036's.....

You are right, but in general, a normal household will have a mix of 5A, 15A and 30A fuses. I think the chances of someone installing 30A wire instead of the 20A when it blows because that's what comes on the standard packs is a little too high for my liking.

 

[RF Lighting]

http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Standard_Range/index.html

Also have a look on ebay. There is often some listed on there.

 

[andy1020]

aah, yes, that's what I'm looking for, thanks. will something like that be available from my local elec wholesalers do you think?

 

[RF Lighting]

Almost all electrical wholesalers will carry them as a stock item. If you can't wiat while monday even the DIY sheds will probably have them (at three times the price)

 

[plugwash]

You are right, but in general, a normal household will have a mix of 5A, 15A and 30A fuses. I think the chances of someone installing 30A wire instead of the 20A when it blows because that's what comes on the standard packs is a little too high for my liking.

agreed, 20A fusewire is a PITA to get for homeowners, its not on the standard packs and the only online supplier i know of that has it (TLC) only has it by the reel.