Will my mcb be sufficent for new heater with current regs?

[duckegg]

Hi

I've got a 32 Amp mcb on my kitchen ring which includes dishwasher, washing machine & tumble dryer all spured off and a fridge and kettle/toaster that are used. It also has a hob spured off of it rated at 5.8Kw! We also want to add a plinth heater which is rated at 1.8Kw, this is a plug in unit with a 13A plug. Is it ok to add this?

I've done some basic maths and the plinth heater and hob both together come to 33 Amps on full load but do the regs allow for the fact the hob / heater wont really ever be used together at full capcity or do I need to put in a new circuit for it?

Thanks!

 

[JohnD]

1) an electric hob should not be supplied from a ring. The largest load appliance that may be connected to a ring is 13Amps (about 3kW) and all loads should be connected via a fused plug or a fused connection unit. Your hob should be supplied via a dedicated cooker circuit. You are currently describing a very unsatisfactory job.

2) If you run more than two of washer/drier/dishwasher/kettle/toaster/oven/fan heater at the same time you can expect to be overloading your ring. It may or may not trip depending on how many of them is on heating cycle at the same time.

If you get a cooker circuit installed for the hob (and oven) when you will probably not get many trips with the rest of the appliances. However it would be an advantage to provide, say, a 20A radial to cope with the washer and drier. A 32A radial would be better but needs larger cable.

It is no good just changing the MCB to a higher rating as the cable will then be overloaded, which is much worse.

As this electrical work is being done in a kitchen it is notifiable under building regulations.

 

[duckegg]

Thanks for your reply John D. My hob is supplied from a 13A fused spur coming off the ring main but using 4mm cable (from the spur to the hob), does this make a difference or is it still not within regs?

 

[ColJack]

the very fact that it's 5.8Kw precludes the posibility that it's off a 13A fused spur since at full load it would be about 25A, more than almost twice the fuse rating..

hobs need to be wired on their own circuit..

it's not regs to have the large appliances on their own radial but it would be a very good idea to do so..

 

[ban-all-sheds]

Thanks for your reply John D. My hob is supplied from a 13A fused spur coming off the ring main but using 4mm cable (from the spur to the hob)

I'd love to meet the guy who decided that 4mm cable was needed when there's a 13A fuse, and have him explain his thought processes....

 

[duckegg]

This is bad news, we had it rewired a while back by a friend of a colleague whos gone awol but was a sparky, thing was when it came to fitting the kitchen nothing had been put in place for the hob, so with my limited knowledge I phoned him and he advised to put a 4mm cable from a 13a connection unit spured off the ring.

We were hoping to get the house tested and signed off to be up to current regs but I suppose we can't now? I cant really re route cables in to the kitchen because it's been fitted.

 

[ban-all-sheds]

This is bad news,

It's not good....

we had it rewired a while back by a friend of a colleague whos gone awol but was a sparky, thing was when it came to fitting the kitchen nothing had been put in place for the hob, so with my limited knowledge I phoned him and he advised to put a 4mm cable from a 13a connection unit spured off the ring.

He really doesn't sound like a competent sparky..

We were hoping to get the house tested and signed off to be up to current regs but I suppose we can't now?

Not really.

From an electrical POV you can now only get a PIR done, but that's not what you should have as a certificate for a complete rewire.

Also, a rewire is notifiable. If the guy who did it did not self-certify, then the only alternative would have been to notify your LABC before the work started. Obviously too late for that now, so there is no way that you can get it certified from the POV of Building Regulations.

Did the AWOL sparky say that he was registered to self-certify Building Regs compliance?

I cant really re route cables in to the kitchen because it's been fitted.

I would strongly advise against plugging anything more into that ring. It won't be unsafe, but you might start tripping the MCB.

And I guess it must be OK in practice, as you're using it, but I'm surprised that the hob is working OK. I know that it won't draw anywhere near 25A for sustained periods, but do you only use it fairly lightly? Have you ever turned all the rings on at once?

 

[duckegg]

Thanks for your reply!

First off we've tried all four hobs on full, 800w Microwave, kettle, dishwasher, extractor fan, tumble dryer & fridge all on at the same time and it hasn't tripped.

We were told when the work was carried out that the sparky himself could not certify the work, which made sense because if any corners had been cut then they would be picked up by a 3rd party. He said that after it had been signed off if I for example added a new socket somewhere that he could come and test that & sign it off as small electrical work / repair (or something along those lines). Does this make more sense?

 

[mdbalson]

What about running a new cable for the hob under the floor cupboards in the kitchen

 

[ban-all-sheds]

Thanks for your reply!

First off we've tried all four hobs on full, 800w Microwave, kettle, dishwasher, extractor fan, tumble dryer & fridge all on at the same time and it hasn't tripped.

It's not the circuit MCB that concerns me - it's a 5.8kW hob on a 13A fuse.

Does anybody know how quickly a 13A BS1362 should operate at 25A?

We were told when the work was carried out that the sparky himself could not certify the work, which made sense because if any corners had been cut then they would be picked up by a 3rd party.

Well I'm afraid you were spun a line there.

1) All electricians should test and certify their own work from an electrical POV, and he knew that.

2) If someone else was going to issue an EIC, then that person should have visited the job during progress to inspect the position and installation of the cables, not just turn up when it was finished and do some tests, and he knew that.

3) Registered electricians can certify their work for Building Regulations purposes, and he should have known that.

4) If he wasn't going to certify Building Regulations compliance then the work should have been notified to LABC in advance, and he should have known that.

5) Unless so notified, and a 3rd-party inspection organised by or in conjunction with LABC, then such an inspection would be worthless in terms of compliance with the Building Regulations, and he should have known that.

So as well as being electrically incompetent, he has been professionally negligent. I know it might be awkward with your colleague, but you really should tell him to stop recommending this "electrician".

He said that after it had been signed off if I for example added a new socket somewhere that he could come and test that & sign it off as small electrical work / repair (or something along those lines). Does this make more sense?

It makes sense that he would tell you that, but it isn't true.

 

[tim west]

a BS1362 plugtop fuse is the same category as a rewireable fuse and can take up to three times its rating for hours before rupturing.

 

[ban-all-sheds]

That's handy...

 

[tim west]

That's handy...

for what?

 

[Adam_151]

As I understand it for a BS1362 fuse, it must be able to take 1.6xIn for half an hour without failing, but when taking 1.9xIn it must fail within half an hour

 

[tim west]

what must rewireable fusewire take?