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gcaxp · May 3, 2007, 07:57 AM

I have a question regarding putting a 20 amp outlet on a 30 amp circuit. I'm replacing appliances in my kitchen, and there's currently a 30 amp, 240V, 3-wire + ground feed to the location where the oven is located, on a 30 amp, double pole breaker. I'm planning to install an electric oven (240V) and a microwave oven (120V). Can I split off a single 20 amp, 120V receptacle for the microwave oven from one of the hot feeds while maintaining 240V for the oven? Would using a GFCI outlet instead of a standard one increase the safety of this installation? Or am I going to be forced to run another line to the breaker box specifically for the microwave?

Stratmando · May 3, 2007, 10:43 AM

You should run new wiring for Microwave.
Most Electric ovens use at least 40 Amps,(#8)for the hots and # 10 for the Ground and #10 for the Neutral.
I always pull #6 for hots, #8 for neutral and 10 for ground to be able to handle about any home oven.Adjust breaker accordingly(see Nameplate)

ballengerb1 · May 3, 2007, 10:48 AM

Stratmando has it pinned. Leave the 240 as a dedicated line and pull new wire and circuit for the microwave. Just to clarify, "20 amp outlet on a 30 amp circuit" your outlet isn't amp rated, the wire and the breaker consistute the max amperage of the circuit.

gcaxp · May 3, 2007, 10:55 AM

Originally Posted by ballengerb1

Stratmando has it pinned. Leave the 240 as a dedicated line and pull new wire and circuit for the microwave. Just to clarify, "20 amp outlet on a 30 amp circuit" your outlet isn't amp rated, the wire and the breaker consistute the max amperage of the circuit.

Then what's the difference between a 15 amp and 20 amp outlet?

ballengerb1 · May 3, 2007, 11:04 AM

The outlet fixture is the same but the wiring inside the outlet leading to the breaker box is heavier for a 20 amp than a 15 amp. The wiring was hopefully matched to your circuit breakers when it was installed. If there have been home owner improvements over the years this matching may be in doubt.

labman · May 3, 2007, 12:18 PM

Most 120 volt outlets are rated for 15 amps. Some devices drawing more than the 12 amps a 15 amp circuit is derated to, use a different style plug rated for 20 amps and require a matching 20 amp outlet. So there are outlets rated for 20 amps. Not that microwaves come with plugs fitting them.

If you did run 120 volt service from a 30 amp, 240 circuit, you would have to run #10 wire. Not everything that will work, meets code. Our electrical expert, tkrussel, has posted a link to the NEC in a sticky at the top of the forum. It is often better to wait for him to explain what it means. Whatever he says, you can trust. I think any outlet within 6' of a sink must be GFCI.

jboughto70 · Jul 27, 2010, 10:29 AM

Actually, there is a difference between a 15 amp and 20 amp outlet and it has nothing to do with the wiring, it is what the internal parts of the receptacle can handle. If you were to run a 20 amp receptacle off a 30 amp circuit, the breaker would allow 30 amps before tripping, which is more than the receptacle is made for, and can cause short circuits and fires, so this is not to be done! You definitely need new wires for the microwave.

stanfortyman · Jul 27, 2010, 01:52 PM

Originally Posted by jboughto70

actually, there is a difference between a 15 amp and 20 amp outlet and it has nothing to do with the wiring, it is what the internal parts of the receptacle can handle.

Not entirely true. The only difference between a 15 and 20A receptacle is the orientation of the slots. The internals are basically the same.

Originally Posted by jboughto70

If you were to run a 20 amp receptacle off a 30 amp circuit, the breaker would allow 30 amps before tripping, which is more than the receptacle is made for, and can cause short circuits and fires, so this is not to be done!

Again, not exactly. The breaker protects the wiring, NOT what is plugged in. Besides, a duplex 20A receptacle is TWO 20A receptacles.
Running more than 20A through it will NOT cause a short circuit. In fact, I am curious as to how you think this is possible.
It can however cause the internal parts to get too hot since it is rated for only 20A feed-through. Even a 15A duplex receptacle is rated for 20A feed-through.
The codes on what devices, receptacles and loads are allowed on what size circuits can be confusing, but they are pretty straight forward.

Originally Posted by jboughto70

You definitely need new wires for the microwave.

You are aware that this thread is over three years old, right? I think the OP is done by now.