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Apologies if covered elsewhere... My place has the old-style three-prong 240V stove outlet, two phases plus neutral. This means the stove (recent, induction) doesn't have a safety ground. The closest ground ever comes to it is if I plug in a grounded appliance on the counter next to it.

The wiring coming to the current outlet is in conduit, so theoretically just replacing the outlet with one that has a ground lug ought to do the job. I just haven't wanted to mess with it; out of sight, out of mind, out of cycles...

I know code says I should fix it. Code is probably right. But must I is gotta do so, or am I probably OK with the grandfathered outlet? I trust this stove more than the one it replaced...

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    Quite sure there are thousands of people with the same setup and never had problems. There are also a few hundred that did touch live housing of the device and did not like it. It is a gamble that nothing ever happens. With conduit, the job is easy, no new cables to run though the walls/floors. Saying that guess I should replace the battery in my smoke alarm I took down a week ago.
    – crip659
    Feb 13 at 17:55
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    Not all conduit has a complete grounding connection to the breaker box/grounding electrode. You should check continuity/potentials on it. Does your stove have a ground connection?
    – Armand
    Feb 13 at 17:56
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    Harper mentions numerous (ongoing) cases that are mostly from dryers, as children get zapped when crawling around them and can't jump away - might be less common with a range/stove/cooktop. But yeah, start with examining the connectedness of the conduit, which should either do the job, or make pulling a dedicated ground wire easy if needed, unless it's just a short sleeve that doesn't end somewhere it's convenient to run a retrofit ground.
    – Ecnerwal
    Feb 13 at 18:04
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    New ones have been banned for over 1/4 century despite the schemes of the appliance industry that kept them 1/4 century after they should have been outlawed.
    – Ecnerwal
    Feb 13 at 18:20
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    Appliance ships without power cord installed, because the house it's being installed in may have a grandfathered 3-contact outlet [1] and the appliance delivery guys aren't certified to replace the outlet if so. So in my case they slapped on the three-wire cord -- as explicitly permitted by the manufacturer -- plugged it in and left. I was aware this wasn't ideal, but I wanted the kitchen back in operation so accepted it while leaving myself a note to reconsider later. [1: This also lets mfgr ship the same model to other countries with center-tapped 220V but different plug conventions.]
    – keshlam
    Feb 14 at 1:03

1 Answer 1

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It is an important safety issue. I would do the following:

  • Double-check the power requirements for the stove. Really. A lot of induction stoves use a lot of power (that's how they can work so well) so you want to make sure they have the right size wires. For example, if the old stove had a 30A breaker and used a peak of ~ 24A and the new stove is rated for a 40A breaker with a peak of 32A then it is quite possible that you could be pushing the wires to their limits without ever getting a breaker trip. Check both the breaker and the wires.
  • If you have metal conduit then check to make sure it is grounded. The easiest way to do that is to check at the receptacle, with the stove unplugged, whether there is continuity between neutral and the conduit. If there is continuity then you have ground and can ground the new 4-wire receptacle or hardwire ground to the metal box. If there is no continuity then there is no ground (even if you have metal conduit - could be a transition somewhere to plastic conduit) and you need to run a new ground wire (green or bare, 10 AWG if 30A and the other wires are 10 AWG, 8 AWG if > 30A or the other wires larger than 10 AWG).

Then you have two choices:

  • Replace the 3-wire receptacle with a 4-wire receptacle. Replace the 3-wire cord/plug from the stove with a 4-wire cord/plug.
  • Replace the 3-wire receptacle with a blank plate. Replace the 3-wire cord/plug with an appropriate 4-wire wire whip, including appropriate clamps as needed to both the stove and the junction box.

And finally:

  • Remove the neutral/ground bond from the stove.

Is this a huge danger. No. But I'd actually posit that while the risk is extremely low initially (large appliances generally don't t have problems for a few years after installation), the risk over time may actually be higher than with a traditional stove. Why? Because with a traditional stove (resistance elements, simple electromechanical controls) the main problems are insulation wearing out or burning up and switch and relay contacts burning up, with induction stoves there are some high-voltage electronics involved that can potentially fail in spectacular fashion. Likely? No. But dangerous if it happens, and that's where the safety protection of a separate ground can be critical.

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    And I should have checked the breaker before first plugging in. Got away with it so far, but that could be because I never have everything running at maximum at once . Reminder appreciated.
    – keshlam
    Feb 13 at 20:52
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    @Ruskes Even today there are devices that don't require grounding and only have two prongs on their plugs (typically things like phone/etc. chargers, lamps, radios, some small tools, etc.). That is not what we are talking about here. Dryers and ovens have been a special exception in code because they are (and for 50+years) designed to be grounded but due to a combination of lobbying and other stuff, they have been perpetually grandfathered in, which combines with end-user ignorance to result in the problem continuing. Every clothes dryer or oven you buy today includes a separate ground
    – manassehkatz-Moving 2 Codidact
    Feb 13 at 23:44
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    terminal. But these appliances (for good reasons, actually) generally do not come with a plug/cord attached and due to the aforementioned grandfathering, one of the options listed in the instructions is "3-wire, no ground". Requiring ground is about much more than conductive housing - that is one key piece but far from the only piece.
    – manassehkatz-Moving 2 Codidact
    Feb 13 at 23:45
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    Which is exactly my case. Device with four internal terminals, but with instructions on how to hook up using a three-contact plug when using a grandfathered, non-grounded, outlet. It was dropped off/installed with the latter, since the appliance delivery folks weren't certified to do house wiring, but I have the option of fixing that. And folks here have confirmed my belief that I probably should find time/energy to do so, when the current batch of projects is whittled down a bit.
    – keshlam
    Feb 14 at 1:00
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    @keshlam The risk of not grounding the appliance is combination of death and fire, of which the manufacturer is well aware of but that's really not their problem anymore. It is probably something you want to worry about though.
    – Nelson
    Feb 14 at 3:37

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