240 VAC Microwave

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shull

Member
Location
Boulder Colorado
Does a wall mounted 240 VAC microwave oven count as a wall mounted oven therefore allowing you to hook the ground to the neutral in the receptacle, if you meet all of the exceptions of article 250.140?? I have a unused 3 wire 50 amp stove circuit and a 4 wire 30 amp New microwave. Will replace old breaker with new 30 amp.
 

Pizza

Senior Member
Location
Minnesota
Usually when an old 3 wire range feed is used for a newer range, the neutral or sometimes it's just a bare wire is bonded to the frame of the range inside the range.
It's not bonded at the receptacle.


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Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The 240v microwaves I have seen are straight 240V and no neutral was needed. IMO, a new microwave would not qualify as an existing circuit for 250.140 to apply.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
What is the make and model of the microwave?

They way the code reads it would have to be 4 wire even on an existing circuit. How many wires are coming from the whip?
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
I agree on both points.

Still the OP should be able to convert the circuit to this new use. :)

I don't think this is the way, though:

therefore allowing you to hook the ground to the neutral in the receptacle

It sounds like he want to replace the three wire receptacle with a four wire one, and do a bootleg ground in the 4 wire receptacle.

To me, the closest thing to proper would be to swap the cord with a three wire cord and do the bonding to the frame of the oven at the oven end.
 

iwire

Moderator
Staff member
Location
Massachusetts
I don't think this is the way, though:

:) I agree.

It sounds like he want to replace the three wire receptacle with a four wire one, and do a bootleg ground in the 4 wire receptacle.

I am going with the theory it is a straight 240 appliance, no neutral needed.

If it really does require a neutral it is new homerun to panel time.
 

user 100

Senior Member
Location
texas
I tried finding info on '240 volt microwaves' and come up empty handed. I wanted to see if the controls and/or displays were commonly 120 volt, as is the case on some regular ranges.

The beast could even be a foreign job that ops customer wants to install here.:D
 

kwired

Electron manager
Location
NE Nebraska
Im going to be honest, Ive never seen a straight 240 volt 60Hz microwave oven.
I haven't either.

If it is something designed to take the place of a traditional wall oven, something tells me it is probably categorized in a similar manner and if original wall oven used the neutral conductor for equipment grounding of the appliance then the replacement likely can as well. Move it to a new location and maybe a new cable with proper equipment grounding is necessary. If you are lucky enough to have existing SE cable as the supply circuit instead of three wire NM cable I see nothing wrong with using the bare conductor for EGC if there is no neutral load in the appliance.

If this appliance has similar supply terminations as many ranges or ovens that has a bonding link for bonding the frame to the neutral, then chances are it is recognized as an appliance that is acceptable to do this with where permitted. (particularly older circuits that originally didn't require a separate EGC).

Doesn't hurt to read the instructions that come with the appliance either:happyyes:
 

iwire

Moderator
Staff member
Location
Massachusetts
I tried finding info on '240 volt microwaves' and come up empty handed. I wanted to see if the controls and/or displays were commonly 120 volt, as is the case on some regular ranges.

I know we install 20 amp 250 volt receptacles for commercial micros, maybe they dont exsit for residential, I do not know.

But if there was any driving factor for requiring a neutral I would say it would be for the sole purpose of using 120 volt lamps for illumination so replacements are readily available.

The electronic controls would have a power supply in any case so likely anything from 120~300 would work.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
But if there was any driving factor for requiring a neutral I would say it would be for the sole purpose of using 120 volt lamps for illumination so replacements are readily available.

The electronic controls would have a power supply in any case so likely anything from 120~300 would work.

Good point. What a PITA to have to find replacement 240 volt bulbs for the interior illumination.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
All of the 240 volt residential microwaves I have run circuits for have required neutrals. GE and Miele are the most common for me.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
I haven't either.

If it is something designed to take the place of a traditional wall oven, something tells me it is probably categorized in a similar manner and if original wall oven used the neutral conductor for equipment grounding of the appliance then the replacement likely can as well. Move it to a new location and maybe a new cable with proper equipment grounding is necessary. If you are lucky enough to have existing SE cable as the supply circuit instead of three wire NM cable I see nothing wrong with using the bare conductor for EGC if there is no neutral load in the appliance.

If this appliance has similar supply terminations as many ranges or ovens that has a bonding link for bonding the frame to the neutral, then chances are it is recognized as an appliance that is acceptable to do this with where permitted. (particularly older circuits that originally didn't require a separate EGC).

Doesn't hurt to read the instructions that come with the appliance either:happyyes:

You make a good point, ones Ive seen count as a wall oven with built in magnetron as a feature. Thus, I would classify that as an oven where pre 1997 rules could apply.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
The beast could even be a foreign job that ops customer wants to install here.:D

If so make sure its rated 60Hz. Capacitors are sized larger for 50Hz to deliver the same power, so that magnetron will be overdriven on a North American supply. On the bright side those hotdogs will better then advertised :cool:
 
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