# Can I use one of the phases in a 2-phase circuit to power a 120V appliance

I am wondering if I can take one of the phases from a 220V circuit that is used to power my cooktop, to power a 120V appliance (small wine cooler) and a 60W LED light transformer.

The specifications for the cooktop are: 220V 6,8kW

The specifications for the wine cooler are: 120V 130W

Unfortunately, I cannot run a new circuit just for the wine cooler which would have been my first option. Right now , the cooktop is running off a 2 pole 40A breaker.

• Do you mean, while leaving the cooktop plugged in? Commented Mar 26, 2015 at 13:54
• @dsolimano yes, the cooler would be always plugged in and running. The cooktop would be used normally, just when we need to cook. Commented Mar 26, 2015 at 14:26
• The circuit is not "two phase" - it's 220V single phase. A common enough misconception. Commented Mar 26, 2015 at 15:38
• I would advise you call your local electrician, they might be able to wire in a separate circuit for you, or do it in a way that doesn't violate code. Commented Mar 26, 2015 at 16:30

As one of the commenters pointed out, this is not 2-phase power (at least assuming something similar to standard U.S. residential 240V single-phase/split-phase service--what country are you in?). It's single-phase power. You get 240V between the poles on the smaller coil of the transformer outside your place. So you get 120V (half) from each pole to the exact center of the coil, where the "neutral" taps in (it's a single-phase center tap transformer). The neutral carries the imbalance between the loads on the two poles (power from one pole is opposite polarity and thus cancels out power from the other). So if there's exactly the same load on each pole, the neutral carries zero current, but it almost always carries some current.

So... yes, technically this would work. But where are you going to tap in? With what kind of device? Are you planning to connect a #8 and #12 wire with a wire nut? ;-)

As another commenter pointed out, you will end up with a 120V appliance running on a circuit protected by a 40A breaker. Since you can't legally put a 15A or 20A outlet on a 40A circuit, that definitely violates code. The device itself isn't going to draw any more current than it needs unless it has a short, but you can't legally wire in an outlet that the appliance cord will fit.

Your 37A calculation is 93% of the rating of the 40A circuit. U.S. NEC says you can't design a circuit with a continuous load over 80% of the circuit breaker's capacity. But "continuous" means full draw for longer periods of time than you are going to operate your stove.

And your cooler only draws about one Amp. So you might be okay there.

So... if you absolutely, positively can't or won't pull a new 120V 15A or 20A circuit from the panel, it sounds like the sanest option (from yet another commenter) is to redirect that 40A 240V circuit into a small subpanel.

I just now saw a little 2 space, 4 circuit 70A capacity subpanel/load center at a major box store's website for \$15. Cheap.

Hopefully the cable you already have running to the stove has 4 wires (2 hot, 1 neutral, 1 ground).

The neutral (grounded) and grounding buses in the subpanel have to be disconnected from each other, the neutral bus has to be isolated from the metal box, and the grounding bus has to be bonded to the box. Otherwise, if there's a fault in the neutral, all your return current ends up on the ground and potentially energizes the box.

Your existing 40A two-pole breaker in the main panel is your master breaker for the subpanel, protecting the existing wire. Put a 40A two-pole breaker in the subpanel to feed the stove, and a 15A or 20A single-pole breaker to feed an outlet for the cooler.

You can use a masonry bit and concrete screws to drill and screw the little subpanel to the concrete, and to secure the conduit or MC that you'll run from that panel to the outlets for the stove and cooler. Which you will secure to the concrete in similar fashion.

You could use a small panel similar to this:

• If you do install a panel, the grounding bus should be bonded to the panel. The grounded (neutral) bus should be isolated from the panel, and the grounding conductors/bus. Commented Mar 27, 2015 at 17:17

You can draw a maximum of 40A from each leg. Watts is voltage times square of current in amps, iirc; you can use that to figure out how many amps each 1-leg device needs. If the total of that plus the two-leg 240V current for the stove is less than 40A, then technically this will work. In fact most stoves these days do this internally; control circuits and the oven light run off one leg.

Whether this is a code violation, I can't answer.

Personally, between code concerns and how much current the stove already draws, I think you'd be wiser to run a new 120V circuit to the kitchen. That'd be easy to do in my place; can't vouch for yours.

• Yes, I did that calculation and got a total of ~ 37A total. I just wanted to make sure that I'm not missing anything obvious. Unfortunately, the buildings here are concrete so I would have to tear down parts of the walls and part of the floor to run a new 120v circuit. Commented Mar 26, 2015 at 14:52
• I am fairly certain that it is against code (and potentially dangerous) to directly connect a 120V 20A (R5-20) outlet directly to one leg of a 40A 240V circuit. The outlet must e protected by a 20A (or lower) breaker. What could be done is run the existing circuit to a small sub-panel, containing another 40A 240V breaker to the cooktop and a 120V 15 or 20A breaker feeding the outlet for the cooler. Commented Mar 26, 2015 at 18:37
• @doxylover: makes sense to me. But I agree that the best approach would be to find out how local electricians, who ate familiar with this kind of construction , would handle it Commented Mar 26, 2015 at 18:43
• 37A is 93% of the 40A breaker's capacity. You're not supposed to have more than 80% continuous load on a circuit. I just thought I'd mention that. This would function, but as another commenter said, you would have a 20A appliance on a 40A breaker. The double pole breaker is really just two single pole breakers with a handle tie or the handles fused. The idea of a small subpanel with a master 40A breaker, one double-pole 40A breaker for the stove and one 20A single-pole breaker for the cooler sounds like the sanest solution. Commented Mar 27, 2015 at 4:30
• @SomeGuy But who said there was no neutral? Commented Mar 28, 2015 at 6:35