Electrical regulations or a con?

[fernicarry]

The oven needed a 50 Amp breaker. Which I thought was a lot.

Unnecessary per my understanding of how diversity is applied to cooking appliances, first 10A of the load then 30% of remainder. Up to 15kW can go on a 32A breaker.

If its on a 50A breaker then bear in mind that *everything* downstream of that needs to be rated for at least 50A, the cable, the isolating switches, connection points etc. so that they can withstand potential fault currents as opposed to normal use. Cooker isolators are usually rated for up to 45A....

Rationale being that for cooking appliances its rare that its going full chat and that won't be for any length of time because of thermostatic control.

As someone else has pointed out the cable and breaker will withstand a mild overload almost indefinitely or even what seems like a rather severe overload of 2x for a surprisingly long amount of time. Your fixed wiring cables are usually rated for up to 70', so from a starting ambient temperature of say 20' that's quite a lot of heating before its in any danger. Some cables are rated at up to 90'.

Its different for other kinds of appliances particularly space or water heaters which are quite likely to run at full power for an extended period of time so the circuit must be designed to accommodate that.

Looked at another way, a 50A circuit running at rated capacity will cost almost 2 quid an hour to run...

 

[steveb]

>Unnecessary per my understanding of how diversity is applied to cooking appliances, first 10A of the load then 30% of remainder. Up to 15kW can go on a 32A breaker.

I just looked, our 81Amp cooker is on a 32a breaker which seems just about right according to that calc above. No problems with tripping even when cooking xmas dinner

 

[Zebra]

My opinion on the original question, as an ex-professional electrician, is that the works mentioned, ie installing some extra sockets and some ceiling downlighters, could be done on a Minor Works certificate. Therefore he will have to test the circuits concerned, and be sure that they are safe to extend, and that they comply with current regulations. This might mean that the circuits affected will have to be installed on a RCD or RCBO (which is how costs escalate - sometimes it ends up being easier to change the consumer unit than fiddle about with providing RCD protection for a few individual circuits...). However, he wouldn't have to test all of the circuits in the house and rectify any problems he found, only those circuits he is working on.

 

[Lime]

My opinion on the original question, as an ex-professional electrician, is that the works mentioned, ie installing some extra sockets and some ceiling downlighters, could be done on a Minor Works certificate. Therefore he will have to test the circuits concerned, and be sure that they are safe to extend, and that they comply with current regulations. This might mean that the circuits affected will have to be installed on a RCD or RCBO (which is how costs escalate - sometimes it ends up being easier to change the consumer unit than fiddle about with providing RCD protection for a few individual circuits...). However, he wouldn't have to test all of the circuits in the house and rectify any problems he found, only those circuits he is working on.

Likewise as yourself and I agree with you.
There appears to be many freshly-qualified electricians who are under the misapprehension that 3036 fuses (i.e. fuses with fusewire) are no longer compliant with BS7671 (the Electrical Regulations) and that the whole electrical installation must be compliant with Part P of the building regulations.
In many instances a total rewire may make sense but, apart from ensuring the existing installation has satisfactory earthing and bonding provision and that it is able to take the extra load safely, no other work is required to existing wiring.
The general rule is that new work must not reduce the safety standard of the existing installation.

There is a recent post on the IET Forum that demonstrates exactly what I am referring to.
http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=102792&enterthread=y

 

[Penners]

My opinion on the original question, as an ex-professional electrician, is that the works mentioned, ie installing some extra sockets and some ceiling downlighters, could be done on a Minor Works certificate. Therefore he will have to test the circuits concerned, and be sure that they are safe to extend, and that they comply with current regulations. This might mean that the circuits affected will have to be installed on a RCD or RCBO (which is how costs escalate - sometimes it ends up being easier to change the consumer unit than fiddle about with providing RCD protection for a few individual circuits...). However, he wouldn't have to test all of the circuits in the house and rectify any problems he found, only those circuits he is working on.

Many thanks Zebra. Actually, after some discussion with the electrician, the CU is going to be replaced, in order to accommodate some replanning of circuits. Having now seen the old CU I reckon this is a good plan. However, your comments about the Minor Works Certificate are very useful.

Thanks also to Lime, for the added comments.

 

[Penners]

our 81Amp cooker

81 Amps?!! :shock:

How many times a week do you fire vitreous enamelling?

 

[steveb]

indeed,
5 induction hobs - 1 x 3Kw, 2 x 2.5, 2 x 2
One grill 2.3Kw
Main over 3.7Kw
Side oven 2.5Kw

How often are all on at full blast at the same time? Never, however if I did I guess the food would not be the only thing getting hot

 

[Penners]

indeed,
5 induction hobs - 1 x 3Kw, 2 x 2.5, 2 x 2
One grill 2.3Kw
Main over 3.7Kw
Side oven 2.5Kw

How often are all on at full blast at the same time? Never

Exactly! Isn't that the premise of the diversity factor? You add together the first 10 Amps and 30% of the remainder. In your case I make that about 32 Amps.