I have just discovered that our 120v microwave oven is tapped into the 240v
stove circuit. The stove circuit is a two wire cable with ground, and the
microwave is connected to one hot wire and the neutral is connected to the
grounding wire of the stove circuit. I'm not an electrician, but I know
intuitively this is not right. What is the major danger? Any ideas for a remedy?
The major danger is the neutral current can show up on the frame of
the stove if you have a fault in the grounded conductor.
In fact if this is not type SE cable it was never legal to hook the
stove up that way and since 1996 it hasn't been legal for new wiring,
no matter what cable you use.
On Wednesday, March 11, 2015 at 2:09:01 AM UTC-4, email@example.com wrote:
Agree with the above. The stove circuit is of the older variety,
with one wire sharing the function of neutral and ground. That is
assuming that the stove has 120V loads as well as 240V loads,
which they typically do. If the stove was just 240V, then the one
wire would be just the ground. Assuming it was wired up years ago
when it was code compliant, there is no issue there with the stove.
What some yahoo did was tap into it for the microwave and that is
not code compliant. The best solution would be to do a new run back
to the panel for the microwave outlet. It would also be an opportunity
to add other receptacles if you need them.
Contrary to what some are saying, assuming all else was done correctly,
there is no fire danger, immediate safety hazard, etc. Like Gfre says,
the danger would be if the ground/neutral were to be cut, disconnected
at the panel, etc. In that case, the metal case of the microwave
would become energized. But even with only the stove, installed to
previous code, the same thing would happen with the stove metal itself and
that was allowed for 50 years without disasters everywhere. The chance
of the one wire being interrupted somehow is very low.
So, it should be corrected, but no need to panic.
On Wednesday, March 11, 2015 at 9:30:28 AM UTC-4, trader_4 wrote:
My stove is old enough to be 3 wire, and it has an outlet for plugging in a coffee pot, microwave, etc.
Does the OP have a separate 120 outlet daisy chained to the stove outlet? That sounds out of code to me.
On Wednesday, March 11, 2015 at 9:41:02 AM UTC-4, TimR wrote:
From what was described, that's indeed what they have and it is a
code violation and should be fixed. The thing I worry about with things
like this is if some yahoo did this,
what else did they do with that circuit and/or the rest of the house
that you don't know about?
Your point is well taken. You wouldn't believe what we have come across. For
instance, the front porch light switch was wired to ground. Turn it on, and the
breaker tripped. It has been an expensive nightmare, and it just keeps on.
Stoves like that have an internal 15A or 20A fuse or breaker for those
built in 120V devices. What the OP said, the outlet is wired directly
to the RANGE outlet. THere is no smaller fuse or breaker. BIG
On Wednesday, March 11, 2015 at 9:30:28 AM UTC-4, trader_4 wrote:
Must be running a bit slow today. I take back part of what I said
above about the possible disconnection of the neutral/ground being
the only safety issue. That is one angle, but there is a big safety issue
here, and that is that the microwave outlet is being protected by the breaker
for the stove. That's going to typically be a 40A or larger breaker.
So, you have a 15 or 20 amp outlet plus the wiring between the outlet
and stove, on a 40A or bigger breaker. That is a potential fire hazard.
On Wednesday, March 11, 2015 at 9:55:03 AM UTC-4, trader_4 wrote:
So you could potentially plug way too many devices into that outlet and never trip anything, that makes sense as the main safety issue.
That 40 A breaker is a double. I'm not sure how they work. Does it take 40 A to trip either side?
Sounds like an Edison circuit. Two circuits on three wires. It is
possible to split a 240 into two 120's using the common neutral, but I
don't know if it is legal to have both voltages. I don't know enough
about the code to say if it is compliant or not.
The only way to eliminate it is to run a new wire either from the
breaker box or from a junction box that can support the additional
The Edison circuit was originally designed by Edison using his DC
system, but he lost out to Westinghouse and AC.
There should not be too much danger as long as you pay the Fire
Department to park and staff a fire truck in your driveway 24/7.
They will likely be able to limit the fire, so it only destroys your
For a remedy, call an electrician, to wire it properly!!!
That outlet is probably not even on a correct size breaker or fuse.
Thanks, guys, for all the input. There are no 120v devices on the stove (very
cheap model). No clocks, outlets or the like. Strictly 240v heating elements.
The house was constructed in the late 60's, early 70's (with aluminum wiring)
and the kitchen "remodeling" was done in 2010, at which time the jerry rigged
wiring was installed. I'm sure no permitting took place.
Glad to learn about the extent and nature of the dangers, though. I will make
sure that there is continuity in the ground between the stove and the
distribution panel. I'm going to go with having a separate circuit installed as
time and circumstances allow.
PS The Anne Arundel County Fire Service was not interested in stationing fire
fighters and equipment in the vicinity. The entire community has aluminum wiring
and yet there have been no house fires that I am aware of.
Thanks again to all of you for your help.
And that outlet is probably wired with #12 or #14 wire, which is
connected to a 40A or 50A breaker. And likely they have copper wire to
the outlet connected to Alum wire, which is likely to corrode due to the
dialectric action of different metals.
What are you going to do, check the connections every day? I'd get that
separate circuit installed THIS WEEK or sooner.
In that case, the whole house might burn to the ground.
Your house could be the FIRST one to burn.
Consider this. The Microwave (MW) develops a problem, causing a dead
short. There is no properly sized breaker to trip. Several things can
happen. If you're lucky. only the MW will be destroyed as smoke pours
out of it, making it hard to breathe and sooting up the house, until it
finally burns the internal wires and components enough to be
disconnected from the power. -OR- If you're not so lucky, the
unprotected #12 or #14 wires to that outlet ignite, setting the house on
fire, destroying your home. It's a gamble, and with Alum wire, the odds
are NOT in your favor. So, you might want to have some marshmallows
handy to roast as your home burns to the ground.
I have not addressed any possible electrocution issues in this reply.
As another poster said "the person who wired that should be in jail".
On 03/11/2015 2:43 PM, firstname.lastname@example.org wrote:
A "dead short" will certainly trip even the 40A breaker instantly.
The actual fire danger is, imo, quite low w/ the single device; where it
would be a serious hazard from that standpoint would be multiple outlets
where one could easily put a normal load that greatly exceeds the
outlet/local wiring heating limits, but that isn't the case here of the
Is it right? No.
Should it be corrected? Yes.
But is it an _imminent,standing_ fire or safety hazard? No.
Take a 20 A circuit in the kitchen. Each appliance used in the
kitchen will normally max out the circuit. Is there a danger with
only the microwave plugged in? Not normally.
Plug a microwave and a deep fryer into the same outlet (on a 40A
breaker). Fire hazard easily.
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