mains incomer rating

[Rob.Garwood]

Hi,

The main isolating fuses (pre electricity meter) in my new house are only rated at 30A. The existing consumer unit (consisting of an isolator switch, one 30A ring main and one 5A lighting circuit - both of wich are re-wirable fuses) will be replaced by a modern consumer unit. To get around the problem of the main incomer fuse being rated at 30A (it is rewireable), I was thinking of upping the rating of the fuse wire (to say 45A) and fitting a suitable RCD double pole main isolator to the consumer unit. My biggest problem is I can only seem to get 80A isolators and don't really want to rely on the 45A fuse wire in the main incomer fuse box. Any advice? Would it be wiser to have the incoming fuse box uprated to 80A by the electricity company? What is the normal rating for these as most I have seen have been rated at 80 or 60 Amps, never as low as 30A. The box itself does say inside max rating 30A as well, so I am concerned about pulling 45A through it.

Thanks in advance for any advice

Rob

[Frank Erskine]

Well you certainly can't uprate this fuse yourself - it belongs to the electricity company and you (officially) aren't allowed to tamper with it. What's the current rating of the meter itself? If that's very low too, it'll have to be replaced.

30 Amp does seem incredibly low - what type of supply is it? Overhead? Are you out "in the sticks"? Methinks you will have to contact your supplier, and pay probably big money for an uprated supply :-(

[Rob.Garwood]

Underground supply and the house (c1930s) is inside the M25 so it is not in the back of beyond. 30A does seem increduously low. The electricity meter (will have to check its rating) was replaced in

2001, the sealing tag on the isolating fuse box is missing so I thought great nice easy diy job. I don't think it will be a case of having a new incomer run to the house as neighbours haven't required this and they have larger loads than 30A on their circuits.

[Colin Wilson]

It sounds like a very old cutout - call through to your local REC and see how you go about getting it changed.

[tinnews]

An "80A isolator" almost certainly provides no protection (i.e. it doesn't have a fuse in it and isn't an overload protection device), it's just a switch capable of switching 80 amps.

[The Wanderer]

Hmm, sounds like it's an old rewireable fuse, I'm guessing also that it's metal-clad. All Area Electricity Boards (pre privatisation) were charged with replacing 30A cutouts many years ago. Needless to say some were more successful than others.

You don't say where within the M25, but contact your local REC (probably EDF, but it may SSE if you're on the west side of London, Hounslow, Ealing, Acton, that sort of area) and tell them you have an old rewireable cutout, and ask them to change it. Don't let them try and charge you for it - they will if they can get away with it - it's their responsibility. Come back if you get any hastle!

I wouldn't bank on it, some very old services were .0145² CSA, and won't be adequate for a nominal 100a supply. Ask them to confirm the supply capability when they get someone round to change the c/o. The guys who come to do the work will be able to identify the cable size.

Again. don't let them try and charge you for upgrading if it's necessary.

[Lurch]

On 13 Apr 2007 05:15:12 -0700, " [e-mail]" mused:

Don't. It's not yours and it's not your responsibility. as athers have said, contact your REC (or whatever they are today).

Why would an RCD main isolator limit any current and assist with a low incomer rating? You should only be fitting RCD main incomers to consumer units if you have problems with Ze (very rare) or (slightly related to the previous) you are on TT. If you do fit an RCD main isolator you shouldn't be using it as the only RCD protection for the whole installation.

An isolator is just that, an isolator. An 80A isolator means it is capable of carrying 80A, not that it will interrupt a supply that reaches 80A.

If by isolator you mean your aforementioned RCD, the same applies. The amperage rating is the maximum it can handle.

In the olden days there wasn't much need for electricity. You really need to contact your electricity company and get some advice on what your current supply can supply and what it may cost to upgrade it if required.

[Rob.Garwood]

Thanks for the advice all.

The main isolating fuse is all metal and does look as old as the hills. I will get onto the electricity supplier to come and upgrade it.

Thanks again

Rob

[Andy Wade]

Are we talking about pre-1937 cut-outs here, with double-pole fusing? If so there's now a statutory duty [*] on the DNOs to replace them by the end of January 2013.

[*] Regulations 2(4) and 7(2) of the ESQCR,

[Colin Wilson]

[The Wanderer]

I'm no longer in the industry. I've only tended to look at whatever I've needed to knock down some of the misinformation you see in discussions here from time to time. :-)

Still, the statutory requirement might help to focus minds....

[Owain]

I wonder if the replacements will last 76 years...

Owain