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5840 posts

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#272951 27-Jul-2020 10:57
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I'm looking at fitting a new induction hob and trying to figure out what size cable will need to be run.  It's a tricky cable run and last time I retrofitted an induction hob, there were issues with the existing power supply.

 

The hobs I am looking at all have a rated load of 11kW. 

 

The existing hob is gas with electric ignition, so minimal existing power supply

 

It's about a 20m cable run from the switchboard.





Mike

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  #2529332 27-Jul-2020 11:02
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Surely it's an electrician's job to figure out that.


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DR

  #2529363 27-Jul-2020 11:24
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Yes, this is a job for an electrician. However, is this 11 kW over a single phase or three phases? In a domestic situation 11 kW over a single phase to an appliance is getting up there. For an EV charger I've got 11 kw over 3 phases for a 10 m run using 2.5 mm^2 cable. 


 
 
 
 


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  #2529370 27-Jul-2020 11:34
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You need to check the spec for the cooktop as usually they wont need the full 11Kw (48A!!) supply as they will cycle or limit elements when multiple ones are on.

 

Most likely in the spec somewhere it will say it needs a 32A supply.

 

 


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  #2529379 27-Jul-2020 11:49
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What's the model number?

 

 

 

20m might push it to 10mm2? 





I'm not a complete idiot, I still have some parts missing.


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  #2529396 27-Jul-2020 12:35
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Our sparky ran 2phase 6mm2 cable for our 11kW induction hob rated at 44amps in our new build. He ran 16mm2 cable for 2 phase connection for mains and submains from outside property.




Do whatever you want to do man.

  

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  #2529403 27-Jul-2020 12:44
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Daynger:

 

You need to check the spec for the cooktop as usually they wont need the full 11Kw (48A!!) supply as they will cycle or limit elements when multiple ones are on.

 

Most likely in the spec somewhere it will say it needs a 32A supply.

 



Probably something like this:

https://www.fisherpaykel.com/nz/kitchen/cooking-appliances/cooktops/90cm-5-zone-touchslide-induction-cooktop1.CI905DTB3.html

 

Yes the 11.1KW / 48A requirement is after accounting for internal load limiters. The sum or the individual elements power ratings is way higher than 11.1kW, but the unit won't let them all be turned on full power at once to keep the electrical requirements reasonable.

 

Still I hope OP has a multi phase supply to their house. 48A is a lot for a single appliance if you only have a single phase supply and an 80A pole fuse...


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  #2529410 27-Jul-2020 13:04
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Lots of factors to be considered, like actual device current rating, how many phases you have available, where does the cable run, what's around it, etc.
An electrician needs to have a look.

But to give you an idea.
11kw single phase is 48A
48A running 20m through house insulation needs 25mm² cable.
48A running 20m clipped to timber and no insulation needs 10mm²
48A running 10m clipped to timber and no insulation needs 6mm²

I'd also question your 20m measurement. Where did it come from. Often a run that looks like 20m can need 30m.

If you want to play with some numbers yourself, download gencalc on your phone.




Electrician.

 

Location: Dunedin

 

 


 
 
 
 


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  #2529486 27-Jul-2020 14:19
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As a general rule, most induction cook-tops that draw more than 16A have the ability to connect to multiple phases. (typically only apartment / motel style 30cm wide induction cook-tops have a power draw this low).

 

My induction cook-top (60cm, 32A max draw) has the ability to feed the left & right hand side off separate feeds, allowing for the load to be shared across different phases. (My house has only a single phase supply So I have the the (included) metal bridge between the two connection screws in place, and It is fed via a single 32A phase supply).

 

The 11.1kW F&P cooktop I used as an example has the ability to split the load across three phases. Generally best to share loads around between phases as much as possible (although each individual phase needs to be checked for capacity to do this).

 

 

 

It is quite likely that installing this appliance will require work on the switchboard, which is strictly prohibited without appropriate licences. Might as well get the sparky in for an initial visit to work out wire sizing and distribution across phases (if relevant).

 

 


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  #2529488 27-Jul-2020 14:22
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When I was looking at what was needed for a Spa my sparky friend said he uses a calculator to work it out.  Either web: https://www.nexans.co.nz/eservice/CrossSectionCalculation.nx or app https://apps.apple.com/nz/app/gencalc/id725309423 or  https://play.google.com/store/apps/details?id=com.generalcable.gencalc&hl=en

 

 





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  #2529562 27-Jul-2020 15:03
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andrewNZ: Lots of factors to be considered, like actual device current rating, how many phases you have available, where does the cable run, what's around it, etc.
An electrician needs to have a look.

But to give you an idea.
11kw single phase is 48A
48A running 20m through house insulation needs 25mm² cable.
48A running 20m clipped to timber and no insulation needs 10mm²
48A running 10m clipped to timber and no insulation needs 6mm²

I'd also question your 20m measurement. Where did it come from. Often a run that looks like 20m can need 30m.

If you want to play with some numbers yourself, download gencalc on your phone.

 

 

 

While the above answers are correct there are some other factors to take in to account. Will your current mains be big enough to support the extra load of the oven?

 

There is a "Maximum Demand" factor you can apply to this.

 

Keep in mind in real life calculating the cable size some factors have to be taken in to account. For example although calculations can allow for no insulation, the reality is at some point in the cable run it will have to travel thru insulation and the worst case calculation has to be used.

 

best advice is get your electrician to do the calculations as that is the reason they have done an apprenticeship, Joe homeowner has no real idea on current calculations and maximum demand calculations and it can go very wrong very quickly, the end result if not done right will be a fire.

 

 


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Ultimate Geek


  #2529747 27-Jul-2020 17:57
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Need to figure out what the actual maximum demand from the cooktop is. It's unlikely to need the full 11 kW, so you can factor in some diversity.

 

andrewNZ:
48A running 20m clipped to timber and no insulation needs 10mm²
48A running 10m clipped to timber and no insulation needs 6mm²

 

You must assume insulation will be installed in walls, ceilings, and underfloor in NZ when selecting and installing wiring systems. (See section 3.4.1 of AS/NZS 3000:2007 w/ Amendment 2).

 

-e- I'll just quote the passage, because it's not long:

 

 

In New Zealand only, wiring systems in domestic installations shall be installed on the assumption that thermal insulation in ceilings, walls and under floors, if not currently installed, will be installed in the future. 

 


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  #2529764 27-Jul-2020 18:55
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As an earlier post suggests, there is more at play than just full load current. In our wiring rules we have tables for calculating maximum demand. Leave it to the professionals.


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Geek


  #2529773 27-Jul-2020 19:31
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Scott3:

 

Daynger:

 

You need to check the spec for the cooktop as usually they wont need the full 11Kw (48A!!) supply as they will cycle or limit elements when multiple ones are on.

 

Most likely in the spec somewhere it will say it needs a 32A supply.

 



Probably something like this:

https://www.fisherpaykel.com/nz/kitchen/cooking-appliances/cooktops/90cm-5-zone-touchslide-induction-cooktop1.CI905DTB3.html

 

Yes the 11.1KW / 48A requirement is after accounting for internal load limiters. The sum or the individual elements power ratings is way higher than 11.1kW, but the unit won't let them all be turned on full power at once to keep the electrical requirements reasonable.

 

Still I hope OP has a multi phase supply to their house. 48A is a lot for a single appliance if you only have a single phase supply and an 80A pole fuse...

 

 

 

 

Its even worse when you account for most pole fuses in NZ are 63A.

 

I would suggest to OP if it is that 48A unit and you only have a single phase supply that you pick another hob.




5840 posts

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  #2530039 28-Jul-2020 12:50
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Actually I made an error, the unit I'm looking at has a rated load of 7.4kW, which should be <32A.

 

https://www.bosch-home.co.nz/productlist/cooking-baking/cooktops/induction-cooktops/PXY875KW1E#/Tabs=section-technicalspecs/Togglebox=-1508568551/Togglebox=1149550223/Togglebox=285469437/ 

 

 

 

Basically I'm trying to figure out of this is at all feasible before I take a day off work and get an electrician on site.

 

If I know the cable rating I need I can get a rough idea whether it's feasible to run.  If I think yes or maybe, I'll engage a professional.  If it looks like a no, I'll get a new gas hob instead.

 

 

 

 





Mike

2257 posts

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  #2530045 28-Jul-2020 13:01
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Depends on the real length and many other factors as we've already stated.

BUT, making some big assumptions you probably need 6mm².





Electrician.

 

Location: Dunedin

 

 


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