Wire size for Oven and cooktop

[Dirty Doogie]

:(( 18 months ago when remodelling and gutting the house I told the Sparky I was installing an electric oven and an electric cooktop and could he please drop and run some cable. He asked what type of cooktop/oven and I said I hadnt chosen one yet. He ran 2 x 6 mm 3 core cables.

Ok last week I got my new oven and cooktop and noticed the oven drew 30 amps and the cooktop 25 amps. Sparky #2 shows up to quote on installation and immediately says the appliances need bigger cables... GRRRR!

Does this sound right? dropping and laying new cables is going to be extremely difficult now all the sheeting is on.

Can 2 6mm cables do the job?

[NCArcher]

I'd try another sparky.
From the information given i would say that a 6mm cable to each of the appliances was easily big enough. (yes I am an electrician)
Having said that the sparky you talked to may know something i don't. Ask him why the cables are too small. If he can't give a satifactory answer dump him.

[elkangorito]

I'd try another sparky.
From the information given i would say that a 6mm cable to each of the appliances was easily big enough. (yes I am an electrician)
Having said that the sparky you talked to may know something i don't. Ask him why the cables are too small. If he can't give a satifactory answer dump him.

I second this motion.:)

[Dirty Doogie]

Thanx NC , I have already booked a 3 rd sparky to give me quote on Monday. I'll see what #3 says. I really hate it when this sort of thing happens.

Doog

[Dirty Doogie]

Ta Elkangorito,

Sparky #2 mumbled something about Load phasing and 10mm cable. :( I dont know ???? He quoted $420 but that included 8 metres of 10 mm cable , a plug for cooktop, a new circuit breaker and about 2 hours work. Seems like a lot to me !!!

[elkangorito]

Ta Elkangorito,

Sparky #2 mumbled something about Load phasing and 10mm cable. :( I dont know ???? He quoted $420 but that included 8 metres of 10 mm cable , a plug for cooktop, a new circuit breaker and about 2 hours work. Seems like a lot to me !!!

Could it be that sparky #2 was talking about load balancing? Is your supply 3 phase? If it's not, I'd ignore sparkie #2 unless thermal insulation (fibreglass etc) is involved.

Here's what AS NZS 3000:2007 says about 6mm squared TPS current ratings. All values relate to 2c+E TPS cable (the flat white stuff with 3 wires in it);

1] Completely surrounded by thermal insulation - 25 Amps.

Generally, this is the worst case scenario. Under "normal" circumstances (cable not running through the any wall/ceiling insulation) you can get 32 Amps out of 6mm cable.


So, is your cable running through thermal insulation? Do you have a 3 phase supply?

EDIT: I don't know what the general hourly rate for a sparky is but based on an assumed $60 per hour;

2 hours = $120.
This means that 8 metres of 10mm cable & a plug will cost you $420-$120=$300.
Way too much if you ask me. But then again, some of the "working" sparkies here may like to elaborate.

[Smurf]

Not sure what the cost should be since where I work we are looking after our own equipment and not doing work for the public.

But it would have to be a pretty big oven / cooktop to not be able to use the 6mm cable, especially with 2 separate cables. Upright cookers (oven, grill and hotplates) are often fine with 1 x 6mm cable so there shouldn't normally be a problem running just the oven or just the cooktop on the same cable.

That's assuming a fairly "normal" oven and cooktop. 4 hotplates, single oven etc.

I suspect either there's something unusual with the oven and/or cooktop, there is insulation involved, or the sparky doesn't know how to properly calculate the cable size required.

P.S. Can any of the electricians on here tell me what the approximate cost should be to install a time switch and meter for off-peak (excluding any charges by the power supplier)? I'm not suitably authorised by the utility to do meter installation (we don't actually have meters where I work, all unmetered supplies) so it's easier to just get someone to put the meter in for me. Meter panel (blank at the moment) and switchboard are already there and up to standard.

[elkangorito]

P.S. Can any of the electricians on here tell me what the approximate cost should be to install a time switch and meter for off-peak (excluding any charges by the power supplier)? I'm not suitably authorised by the utility to do meter installation (we don't actually have meters where I work, all unmetered supplies) so it's easier to just get someone to put the meter in for me. Meter panel (blank at the moment) and switchboard are already there and up to standard.

This is "off topic" but just quickly...
Smurf, I assume that you are a sparky. If this is the case, there is nothing wrong with you buying & installing the meter base(s) onto the meter board. I'm sure you're aware that it must, however, be checked by someone who is authorised to check it. The same goes for the "time switch". BTW, what is the "time switch" you speak of? Is it solid state or electromechanical?

[nev25]

noticed the oven drew 30 amps

What sort of oven is it
Must be one hell of a big oven Ive never seen one rated that high

[another termite]

What sort of oven is it
Must be one hell of a big oven Ive never seen one rated that high

I agree a cooktop yes but sounds pretty high for an oven.
Just had a look at the new 3000:2007 rules and as long as the cable is only partially surrounded by thermal insulation it is good for 32 amps (table C5) So clipping it up to a piece of timber above the thermal insuation will get you to your 32A rateing (of course in reality it shoud be clipped most of the way anyway) Or is it just me that interprets partially surrounded as when cliped to timbers... tech was a long time ago.

[Smurf]

This is "off topic" but just quickly...
Smurf, I assume that you are a sparky. If this is the case, there is nothing wrong with you buying & installing the meter base(s) onto the meter board. I'm sure you're aware that it must, however, be checked by someone who is authorised to check it. The same goes for the "time switch". BTW, what is the "time switch" you speak of? Is it solid state or electromechanical?
True. But I figure that if they're going to check it then they may as well just install it as probably won't be much different in cost given that it's only a minimal amount of work.

As for the time switch, Aurora uses both types. The new ones are generally solid state but they do recycle the older electromechanical ones as they last just about forever. There is no frequency injection system used in Tas for domestic off-peak switching.

In some states I think the utility will still connect the meters too(?) and won't actually let contractors put seals on etc. It's pretty much the other way around here - but only their "authorised contractors" are given meter sealing tools etc which makes it a tad complicated for any electrician who doesn't do enough of that sort of work to justify gaining the required authorisation. For a one-off it seems easier to just pay someone to do it.

[Dirty Doogie]

HEe! Hee! Thanx for your info guys. Sparky # 3 just came and quoted - about $200 and he said the 2 x 6mm cable were fine.

The oven is a fisher & paykell single oven which in the literature at point of sale states it draws 20 amps - however when you get it out of the box there is a warning sticker saying that under certain settings the oven may draw 30 amps.

Thanks again guys Doog

[nev25]

Whats the model number I'd be curious to have a look
(Its not 110V is it)

Off the topic

.
In some states I think the utility will still connect the meters too(?) and won't actually let contractors put seals on etc. It's pretty much the other way around here - but only their "authorized contractors" are given meter sealing tools etc which makes it a tad complicated for any electrician who doesn't do enough of that sort of work to justify gaining the required authorization.

I'm in East Vic (under SP AUSNET) and we are not allowed to seal meters
even thou I have done a course on meter replacement (Worked for a company that had a contract to replace domestic Single Phase KW Meters)

I'm wondering where else in Australia are REC allowed to replace meters without a truck appointment