Electrical work needed for induction hob?

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StackofWaffles

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#290766 3-Dec-2021 01:10

Hey all. I recently bought a new place that's kitchen was very recently renovated. Electricals were done by a qualified sparky.

It came with a ceramic cooktop (7400W/25A) and an oven (15A) connected on a single circuit relying on an old 30A ceramic fuse on the switchboard. The ceramic cooktop is wired with a 4mm2 thick cable that's about 30cm long from the cooktop to the junction box (where it joins the oven circuit). The cooktop is on the 2nd story, right onto of where the switchboard is downstairs, so roughly 3m length.

I'm wanting to install a new induction cooktop that will draw 32A on max draw so I've called in a sparky to get a quote.

Now the sparky said the wiring from the switchboard to the kitchen is new and fine, however he says we will have to do the following:

- Swap the old 30A for a circuit breaker

- Change the wall switch from a single hob switch to double switch (1 for the cooktop, 1 for the oven). Which apparently is ~$70 from PDL.

- 2-3 hours of labour

So I'm not the most clueless guy when it comes to electrical things but this seems a bit over the top, especially the labour and the new wall switch. I've changed my own lights, wall plugs, switches, so I know what's required. I just can't do the necessary calculations confidently.

I'm thinking that I legally should be able to do this myself considering it's a 'like for like install'. Assuming the 4mm2 cable is fine, I just need to buy a new 32A plug-in circuit breaker from Bunnings and wire in the new induction cooktop. I don't even think having seperate switches for the cooktop and oven is even necessary? I was thinking I would need at least a 47A (32A + 15A) circuit breaker but it doesn't look like those exist.

Would any resident sparkies here have any opinion? If I can indeed do this myself, would rather do so to save some cost.

Thanks in advance.

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#2823455 3-Dec-2021 01:20

I would suggest making sure you get a fixed quote price, rather than that sort of very vague estimate.

mkissin

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#2823502 3-Dec-2021 08:28

Since you can only replace like with like, I would think that uprating your breaker to 40A (which is the next size up) would immediately negate your ability to do the work legally.

Dingbatt

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#2823557 3-Dec-2021 08:37

Not a sparky but I would not be diy-ing stuff as dangerous as electricity. Particularly high current stuff like ovens and hobs. If for no other reason than uncertified work provides an out for an insurance company. You could argue “like for like”, but they may see it differently.

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mdooher

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#2823572 3-Dec-2021 08:55

You don't need two switches, check the rating on the one you have, and at worst swap it out for a 40A one

Ref: AS/NZS3000 Section 4.7.1

Matthew

Blurtie

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#2823585 3-Dec-2021 09:28

Not a sparky, but my understanding was that any switchboard related work was a big no no in terms of DIY...

mkissin

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#2823593 3-Dec-2021 09:35

Blurtie:

Not a sparky, but my understanding was that any switchboard related work was a big no no in terms of DIY...

100% right, but they do sell retro-fit circuit breakers that push into the existing cartridge fuse holders for just this reason. If you were to swap the holder itself, that would not be OK.

FineWine

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Nurse (R)

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#2823597 3-Dec-2021 09:42

I have a double wall switch - Hob & Oven - and love it. Especially as I have a touch control ceramic Hob. I quite often turn the Hob off at the wall so I can use the Hob as more bench space for; Slow Cooker etc.

Whilst the difficult we can do immediately, the impossible takes a bit longer. However, miracles you will have to wait for.

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timmmay

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#2823602 3-Dec-2021 09:54

Urgh, ceramic. But yeah his estimate sounds reasonable. If you ask people for a quote then they will build in a margin for risk / overruns.

SATTV

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#2823612 3-Dec-2021 10:20

Sounds about right to me, you cant do anything on the fuseboard, you have to get a sparky in to do this.

The sparking is probably just covering their backside in case they need to make any cuts in the benchtop to make the new hob fit, or when they open up the old fuseboard something else breaks, fuse carriers have not been used since the 80s and plug in MCB's have not been legal in years if I recall, so they will have to remove the old fuse carrier and put in a MCB.

It all sounds like easy work but one small thing can blow out in time.

Personally I would not like to be working in an old fuseboard like that, they can be an atomic mousetrap.

Dont be surprised if they recommend that you upgrade the fuseboard as well, there will be a time soon when you are forced into it.

John

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mattwnz

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#2823905 3-Dec-2021 16:55

timmmay:

Urgh, ceramic. But yeah his estimate sounds reasonable. If you ask people for a quote then they will build in a margin for risk / overruns.

It avoids disputes. From my experience where the final bill was more than double the estimate, because it took them longer than they expected, IMO it is always worth getting a quote. However an estimate should be within 10-15% of the final cost so shouldn't make much difference if they get a quote or an estimate in terms of the price, as it shou dbe wihin 10-15%anyway. https://www.consumerprotection.govt.nz/general-help/guide-to-buying-smart/quotes-and-estimates/#estimates
It can work both ways if it does end up taking a lot longer, but these tradespeople should be good at knowing how long something should take. In my case they weren't experienced.. Also the OP should get other quotes too, as there can be a huge difference between them. If someone doesn't need/want the work, then they may quote very high.

gregmcc

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#2823959 3-Dec-2021 19:15

So you want to give DIY electrical a go. Most important thing is "Are you competent?" How do you know the 4mm2 cable is fine, have you done the calculation?

As far as replacing the ceramic fuse with a 32A plug in circuit breaker, replacing the base on the fuse board that takes the plug in circuit breakers is something a homeowner is NOT allowed to do, if your not going to replace the base and just plug the the new 32A breaker in you will have a problem as the bases were only ever good for 15A when brand new, the plug in circuit breakers do not fit the 30A ceramic bases.

Any changes you (as a homeowner) do to your fixed wiring must be signed off by an electrical inspector - not an electrician before they are put in to use.

There are other things to consider, you could be adding significant load to the house, are the mains big enough to handle this?

All things considered it will cost you more to do this DIY, not only is the calculation for the cooktop and oven wrong (there are other factors here you don't know about) there are potential upstream issues you may have overlooked.

Get your fixed quote from your electrician and get them to do this, they do this kind of stuff all the time, they have at least 4 years of training to do this stuff and they are legally required to issue paper work that says this compliant and safe to use.

Remember poor electrical work at best results in it not working, at worst it start a fire.

Handle9

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#2823969 3-Dec-2021 20:07

I’m really struggling to see how the quote is over the top. 2-3 hours of labour is reasonable for a fixed price job.

You can do it on charge up if you are confident that the job will faster than that but it probably won’t be.

Zeon

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#2824111 4-Dec-2021 07:41

Do you think you will use all the hobs and oven at full boar? Remember that the fuse is there to protect the cable and whatever is currently installed should be suitable for the cable. Why not just replace the cooktop and if you have issues in the future with the fuse blowing then get an electrician in to replace it?

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Bung

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#2824133 4-Dec-2021 09:24

Not a sparky but should the earlier wiring replacement for hob and oven been done without replacing the old fuse with a breaker?

I'm in same predicament having to pay for work that should have been done for previous owner when they had changes made.

chriswiggins

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Ultimate Geek

#2824144 4-Dec-2021 10:03

I’ve just done a kitchen renovation and had to run new cable for the induction hob and the same for the oven.

If your induction hob draws 32a, you need a separate 16a circuit for the oven. The reason for the two switches is as both appliances are “directly connected” to power, you need to be able to isolate them in case there’s a fire. Apparently there are some laws about how far from the appliances you can have them (which is why just having the fuse won’t suffice)

I have 6mm cable for the 32a circuit, and 2.5mm for the 16a.

I also used to have a ceramic cooktop on the same circuit as the oven, but the higher draw of the induction means you need two

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