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How can I repurpose an existing 40 amp 220 volt circuit that services a central air conditioner outdoors to a 30 inch induction range in the nearby kitchen that requires a 40 amp circuit? The existing installation is a 40 amp breaker in the 100 amp main panel connected to another 40 amp breaker in a sub panel box. The service uses 8-2 wire (three wires 8 gauge of White Black and unsheathed ground copper). The length of the run is approximately 60 feet to the AC compressor. The new use of the wire would be just 55 feet to the planed induction range. I plan to replace the AC compressor in a new location. From what I can discern, the GE induction ranges can use a three wire receptacle or a 4 wire receptacle of a 40 amp service. But there might be some advantage to the 4 wire solution which is also the current code requirement. I don’t know if I can repurpose the three wire service and stay in code. Alternatively, I can add a single 8 gauge wire to be the neutral to the existing 8-2 wire for the existing run but I don’t think that is copacetic with any version of the electrical code either.

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  • If I understand correctly, The old AC used two hots and ground, which is okay. The new stove uses two hots, a neutral, and ground. You can add a separate/new ground wire, but not any other wires. You need a 8/3 cable(plus ground).
    – crip659
    Commented Mar 28 at 0:03
  • Yes, I understand the 8/3 solution.. ie pulling new wire. . Can I get away with just using the 8/2 wire with the appropriate receptacle and be grandfathered under the code? Commented Mar 28 at 0:09
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    You cannot install a new NEMA 10-30 receptacle (using bare as neutral) where there wasn't one before.
    – nobody
    Commented Mar 28 at 0:14
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    NEMA 10 was banned in 96. The old AC used NEMA 6. NEMA 10 is only grandfathered If you only replaced the receptacle/plug on a NEMA 10 circuit. You do not have NEMA 10 so cannot make one now.
    – crip659
    Commented Mar 28 at 0:27
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    @crip659 "The old AC used NEMA 6" It is highly unlikely that an AC on a 40A circuit used a plug and receptacle.
    – nobody
    Commented Mar 28 at 0:27

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There are 3 different ways that a 240V large appliance can be powered in typical US homes:

  • 240V only = hot/hot/ground - this is what you have right now for your air conditioner. When used with a a receptacle, this is a NEMA 6 receptacle type.
  • 240V/120V with ground = hot/hot/neutral/ground - this is for any new (and that really means since 1996 or possibly before) 240V/120V appliance such as an oven, clothes dryer or similar appliance. When used with a receptacle, this is a NEMA 14 receptacle type. This is referred to in appliance installation manuals as a 4 wire connection.
  • 240V/120V with ground combined with neutral = hot/hot/neutral - this is obsolete. When used with a receptacle, this is a NEMA 10 receptacle type. This is dangerous because under certain failure modes it can electrocute people. This is referred to as a 3 wire connection.

For historical reasons, cords/plugs and receptacles are readily available for NEMA 10 3-wire connections. But the correct thing to do when faced with that problem is to switch the 3-wire components to 4-wire and not 4-wire to 3-wire. But that actually doesn't matter in this instance because a two-wire plus bare ground cable can never be used for a 240V/120V appliance because that bare ground can not be repurposed as neutral.

So that leaves only two options:

  • Run a new cable (or wires in conduit) with hot/hot/neutral/ground (a.k.a., a /3 cable)
  • Find an appliance that is 240V only and does not have any 120V components.

It is relatively easy to design modern appliances to use only 240V components. A clothes dryer, oven or induction cooktop is basically a large heating element of some sort (induction being more complex than a simple resistive element, but the idea is the same - turn lots of electricity into heat) plus controls, lights, etc. If you look at almost any modern computer you can see that controls, lights, etc. can easily be powered by a full range from 100V to 250V. There are two reasons appliance manufacturers make 240V/120V appliances:

  • Inertia - they've done it for a long time and this allows reuse of the existing receptacles, wiring, etc. with no changes. This is more of a reason for clothes dryers than for ovens and cooktops.
  • Common components between gas and electric - if a clothes dryer uses the same motor, light and controls for gas and electric models then it makes sense to use 120V for those components in the gas model (so that it can use an inexpensive 15A or 20A 120V circuit) and then to reuse those exact same components for the electric model (to simplify design, manufacturing and spare parts).

But induction cooktops are something very new. I don't think you'll find an "almost identical" induction cooktop and gas stove - they are quite different. Plus induction cooktops may require more power than the cooktops they replace, so new wires/circuits may be needed anyway. There is no reasons that manufacturers can't make a pure 240V induction cooktop/range/etc. for the US market. But do they?

In a quick search on homedepot.com, looking at Bosch, Samsung, LG and KitchenAid, some of them clearly require a 240V/120V connection including neutral. Some of them are a bit vague, with one manual indicating the white wire (neutral) is not always present! So there is some hope.

But in the end, probably your best bet is to run a new 4-wire connection. In addition, when permitted by the manufacturer, I highly recommend a hard-wired connection rather than plug/receptacle. Many manufacturers allow either method, but some provide a factory installed 4-wire cord/plug and do not allow hardwiring.

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    Problem is you need to dig deeper into the installation instructions. 40A @ 240V tells you (a) circuit and wire size (8 AWG is good) and (b) how much capacity you need (a.k.a., Load Calculation). But it doesn't necessarily tell you whether you need a neutral or not. 120V/240V or 240V/120V normally means "neutral required" but 240V by itself is ambiguous. Page 9 of the Bosch manual references 120/240 and 120/208 - which means "needs neutral", and page 10 shows a neutral connection separate from ground. Commented Mar 28 at 2:13
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    WUFF CAFE induction range..... " According to page 2 of your installation guide, you must use a single-phase, 120/208 VAC or 120/240 VAC, 60 hertz electrical system. Also, if you connect to aluminum wiring, properly installed connectors approved for use with aluminum wiring must be used. In addition, use only a 3-conductor or a 4-conductor UL-listed range cord. These cords may be provided with ring terminals on wire and a strain relief device. A range cord rated at 40 amps with 125/250 minimum volt range is require" So why the choice of 2 cords? A .4 wire connection = 4 conductor cord! Commented Mar 28 at 3:33
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    The choice of the 2 cords is the NEMA 10 (3 wire) vs. NEMA 14 (4 wire) issue. TL;DR used to be no grounding == NEMA 10. Grounding added in 1960s == NEMA 14. For "reasons", allowed using neutral as ground for limited time. Finally in 1996 banned, but still allowed in retrofit/repair. But (aside from not being a good idea anyway), that doesn't work for you because your 3-wire is hot/hot/ground, not hot/hot/neutral - i.e., old neutral could also be used as ground together with it, under limited circumstances. But modern ground can not be also used as neutral under any circumstances. Commented Mar 28 at 3:41
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    Thanks all, Everyone's comments make perfect sense now. I hope the existing cable is long enough to reach the garage for an EV charger! Commented Mar 28 at 4:06
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    A fourth option is that it's three conductors, in EMT acting as the ground.
    – Mazura
    Commented Mar 29 at 22:01

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