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EDIT 3: Going to end up going with Harper and crip659 on this one. I honestly was worried that there was a justification to have this set up in the way that it currently is, but seeing as no one seems to be able to justify such a bizarre design choice I'm going to just remove the receptacle and the sub panel as it's the safest thing to do. Thanks to everyone who contributed! EDIT 2: More updates, this time to the graph + added details on cooktop. EDIT: Adding details, updating diagram + adding pictures.

Looking for some advice on a little situation I have going on in the kitchen. We've recently had to upgrade our cooktop as the old one had several elements that had just stopped working.

The situation: The cooktop is wired to a 40amp breaker in the main panel which terminates as a 240 volt outlet in the kitchen and that outlet actually has a subpanel plugged into it (AWG of plug is 2AWG) that then connects to the cooktop(cooktop's wires are 8AWG). The part I'm confused about is that the subpanel has two single pole 20 amp breakers (one for the red led and one for the black led) but everything I look up is leading me to believe this appliance should be on a 40amp breaker. Why would someone wire it in this way? I need to replace one of the breakers as I misplaced it when changing them out, so I want to know if I should just buy a 40 amp breaker or stick with how it was originally installed.

Additional Details:
Subpanel: Square D QO Load Center Cat.QO 6-12 T Series L4 (rated for 100 Amps max, 120/240 v I PH. 3W.
Old cooktop: 240v - 8.1kw.
New cooktop: 240v - 7.8kw AWG of wire running from the plug to the subpanel - 2AWG AWG of wire running from cooktop - 8AWG

Cooktop Info FORNEBO (IKEA) Induction Cooktop with downdraft ventilation https://www.ikea.com/ca/en/p/foernebo-induction-cooktop-int-extractor-70537757/ Voltage: 240/208V Connection rating: 7400W Current: 32A

Diagram Diagram

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Litmus99
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    where is the subpanel located? does it have permanent 30in clearance in front of it? if not then you are in violation of code – aaaaa says reinstate Monica Jul 25 '23 at 21:06
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    I am not sure if a sub panel can be plugged in, but I doubt it. The breaker size in the sub panel will depend on what the stove's instructions say. It might be cheaper and easier to plug the stove in, than maybe having to rewire(remove the plug) the sub panel. Not enough info right now. – crip659 Jul 25 '23 at 21:06
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    What size wire goes to the plug?, to the sub panel? and to the cook top? – JACK Jul 25 '23 at 21:15
  • @aaaaasaysreinstateMonica Thanks for the flag, it's about 24"+ in clearance as it's in a kitchen cabinet. I'll have to check our local code in Quebec to look into that, the electrician that reinstalled my main panel told me there was no problem with keeping the breaker box closed off (the main breaker is behind two window shutters. Maybe it's different for a subpanel...(or maybe he was wrong). – Litmus99 Jul 25 '23 at 21:53
  • One of the experts here will explain this, but that plug you show has two hots and one other for three wires total. The odd one is either a neutral or a ground and it makes a difference which one. It could be that your cooktop only needs 240 V and not 120 V in addition so it would not need a neutral, but you need to read the instructions on the new cooktop. Specifically the installation instructions for the new cooktop will state something about the breaker size. But you show four wires in the subpanel. Where is the fourth wire coming from? Do you have four wires in the cable from the panel? – Jim Stewart Jul 25 '23 at 21:59
  • @crip659 The stove requires 240v and 40 amps. I'm not sure I understand the bit about whether or not the subpanel can be plugged in...it is plugged in and worked alright with the old cooktop. Also I'm not following your recommendation...I can't plug the cooktop in as it's meant to be hardwired as per the instructions. I might be misreading or misunderstanding your comments though, so apologies if that's the case. – Litmus99 Jul 25 '23 at 22:01
  • @JACK Good questions, size of the wiring according to measurements of the wire diameters: 2AWG from main panel to sub panel (plug wire) and for the cooktop wires are 8AWG. I'll update the question, thanks. – Litmus99 Jul 25 '23 at 22:01
  • Is this a cooktop only or a stove with a cooktop and an oven? Is this a resistance cooktop or an induction cooktop? Do the instructions state it requires a 40 A breaker minimum? – Jim Stewart Jul 25 '23 at 22:03
  • If the appliance states that a 40 A breaker is required, you would not be able to connect it through two 20 A breakers. You do NOT add the two 20 A breaker capacities to give 40 A. – Jim Stewart Jul 25 '23 at 22:11
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    You need to go by the the instructions. All sub panels I have seen/read about are all direct wire to the main panel. It is usually better to limit the number of different connections, so needing the stove to be hardwired, it would nicer/better if the plug and sub panel was not needed, just use the box the plug is in as a junction box(if it is big enough). – crip659 Jul 25 '23 at 22:11
  • @crip659 Yeah, definitely an avenue I think I'll look into. Thanks! Still really wonder why this was done though...Through my laymen eyes, it seems like a very roundabout way to connect a cooktop in the first place (in speaking about the original installation with the subpanel). – Litmus99 Jul 25 '23 at 22:28
  • @JimStewart, thanks for the detailed questions. Added all that info to the question, but it's just an induction cooktop, no oven. The instructions just show the connections being made with some basic information (black to black, red to red, etc.). The webpage lists the appliance at 32 amps though. Also big thanks for clearing up the 20 amps bit of the question. I'm still scratching my head at how the last cooktop was able to function properly with two 20 amp breakers (the cooktop took more amperage than this one). – Litmus99 Jul 25 '23 at 22:36
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    @JimStewart I forgot to mention I had made a mistake with my original diagram, the 240 volt plug actually has four prongs, not three (three flat prongs and one rounded one for the ground). – Litmus99 Jul 25 '23 at 22:38
  • Do the (hard)wiring instructions state that a neutral is required? I assume that the unit requires 240 V (since you quoted black to black and red to red) but do the instructions also say something about white to white? – Jim Stewart Jul 25 '23 at 23:54

1 Answers1

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You must follow instructions and labeling

... when installing electrical equipment. It was entirely improper for the last guy to "freestyle" the subpanel, individual breakers, and wrong size of breaker.

I guarantee you the instructions and labeling are calling out a 40A breaker.

So the subpanel should be removed altogether, and simply plug the cooktop into that in-wall socket.

If there is a need to power both a cooktop and an oven from that circuit, ask a question about that - there are ways to power oven+range on the same circuit.

Harper - Reinstate Monica
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  • But could the instructions state to hard wire it and make no reference to a receptacle that a cord with plug goes into? If there is a NEMA14-50R in the wall it would sure be convenient to just get a cord with a 14-50P on the end, connect that to the connection block of the cooktop, and plug it in. With an expensive new cooktop would it be prudent to use a voltmeter to verify that the receptacle is wired correctly? – Jim Stewart Jul 26 '23 at 00:53
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    @Jim then get rid of the receptacle and hard-wire it. – Harper - Reinstate Monica Jul 26 '23 at 01:12
  • Would you have to put a box extender on the box with the NEMA 14-50R to make room for a hardwired connection? – Jim Stewart Jul 26 '23 at 15:25
  • @Jim don't know, you'd have to look at the cubic inches of the box that was there. But it'd be easy enough if needed. – Harper - Reinstate Monica Jul 26 '23 at 17:32
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    Funnily enough, I did just that as the wires felt really cramped in the box and I could only find 4 11/16 blank junction box covers (ideally I would have needed one with a knock-out as the box is embedded in the wall). – Litmus99 Jul 27 '23 at 02:08
  • @Litmus99 so you have this unit installed? The unit came with a cord (whip) already on it terminating in bare wires? Or did you have to provide a cord? Instructions really did say hardwire and made no mention of the option of attaching a 14-50P on the end of the cord and plugging into a 14-50R? What is the brand of this cooktop? What is the max power of the largest burner? – Jim Stewart Jul 30 '23 at 09:57
  • @Litmus99 what connectors did you use for the hardwired connection? Was the house wiring for this circuit copper or aluminum? – Jim Stewart Jul 30 '23 at 10:05
  • @Litmus99 What is the final connection--hardwired or through the existing NEMA 14-50R via a 14-50P? – Jim Stewart Jul 30 '23 at 10:26
  • @Jim ranges and dryers typically have exchangeable cords so you can go any way you want. – Harper - Reinstate Monica Jul 30 '23 at 18:19
  • @Harper-ReinstateMonica I have installed ranges and dryers, but never a cooktop. I wondered whether this induction cooktop had the same kind of connection block as those or instead had a factory installed cord connection that would thwart substitution by an installer. – Jim Stewart Jul 30 '23 at 19:39
  • @Jim I would think so, since cooktops and ovens are generally allowed to share the range circuit, and even use the Tap Rules (only residential use of the tap rules). – Harper - Reinstate Monica Jul 30 '23 at 20:25
  • @Harper You have made a reference to this before without calling it "Tap Rules". Could you sumarize it or give a link? – Jim Stewart Jul 30 '23 at 22:54
  • @Jim 220.55 allows the circuit sharing. Tap rules are here https://www.ecmag.com/magazine/articles/article-detail/codes-standards-applied-tap-rules – Harper - Reinstate Monica Jul 30 '23 at 23:38