dimming microwave

doityourself said:

my microwave oven dims when I use it. I got a new one and it does the same thing. This is a old house and the lights dim when the refrigerator turns on. Can someone tell me what is wrong?

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High resistance upstream. Maybe just the circuit feeding the kitchen. Could be a fire hazard. Check it with a voltmeter.

Overloaded circuits is what it sounds to me. You may need to run a couple new circuits in the kitchen. You are supposed to have at least two small appliance circuits for the counter tops. Maybe a new dedicated circuit for the micro and range hood and one for the fridge. Old houses are notorious in this regard.

Overloaded meaning. . .
the breaker is sized correctly for the wire but the wire is so long that, under a heavy load, the voltage drops excessively?
Like over a 5% drop?

No. Overload meaning, to many appliances on the same circuit.

We just put a window AC in our kitchen. Turns out you cannot run a fridge, microwave, and AC on one circuit. :jester: Guess I'll pull a dedicated circuit this week.

You can put off the new circuit decision indefinitely by lengthening (by splicing) a power cord for one of these appliances so that it's long enough to reach an outlet that's on another CB.
You'll need heat shrink tubing and a soldering iron.

Yoyizit said:

You can put off the new circuit decision indefinitely by lengthening (by splicing) a power cord for one of these appliances so that it's long enough to reach an outlet that's on another CB.
You'll need heat shrink tubing and a soldering iron.

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Funny, I would have thought that you electrical types (JOKE) would frown upon a 25 foot extension on a microwave cord. Yes, that's right. Turns out my entire kitchen runs on one circuit (except: oven 220 and garbage disposal - dedicated).

Here are my famous last words: it is only a 15 foot pull from the breaker box to the rec, no problem, right? :laughing:

Leah Frances said:

We just put a window AC in our kitchen. Turns out you cannot run a fridge, microwave, and AC on one circuit. :jester: Guess I'll pull a dedicated circuit this week.

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Leah. Pushing the envelope huh? :wink: I personally like to put the microwave and range hood on the same circuit. Fridge on its own. Then the counter top requirements.

Scuba_Dave said:

How powerful is the new microwave? Old one?
Is it a 15a circuit ? 20a circuit?
What is your main panel, breakers/ fuses?
60a, 100a 200a ?

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Start laughing, please. Old microwave came with the house and was replaced because it only worked if you slammed the door REALLY hard. Turns out the plug was fried...Should that have been my first clue?

New microwave is 1250W Panasonic (120V) 12.7A [AC is Kenmore window 6000BTU listing 15A (115V)].
It's a 20A circuit running from the main panel (breakers) 200A.

I looked at the AC manual and it says, "A 115-volt 60 Hz, AC only, 15A fused and properly grounded electrical supply is required. A time delay fuse or time delay circuit breaker is recommended. Use a dedicated circuit, serving only this appliance." My emphasis.

Well, DUH! Maybe that's the problem. I guess I'll have to go buy some 14/2. Do you think it's a problem that I have three of these units running on another circuit in the house?:laughing: I guess they're rarely on at the same time. :laughing:

Leah Frances said:

Turns out the plug was fried...Should that have been my first clue?
. . .Means high contact impedance from a worn-out receptacle. . .

New microwave is 1250W Panasonic (120V) 12.7A [AC is Kenmore window 6000BTU listing 15A (115V)].
It's a 20A circuit running from the main panel (breakers) 200A.

I looked at the AC manual and it says, "A 115-volt 60 Hz, AC only, 15A fused and properly grounded electrical supply is required. A time delay fuse or time delay circuit breaker is recommended. Use a dedicated circuit, serving only this appliance." My emphasis.

Well, DUH! Maybe that's the problem. I guess I'll have to go buy some 14/2. Do you think it's a problem that I have three of these units running on another circuit in the house?:laughing: I guess they're rarely on at the same time. :laughing:

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If you lengthen the cord to 25' you might want to go one click heavier on the cord AWG.
Whatever CB it finally lands on, you might want to alter the CB trip curve in the "time delay" direction.

So, some rudimentary testing today (thanks Mom for standing in the Kitchen with the voltage meter and shouting to me!) showed that exactly one of the six sets of duplex receptacles is ACTUALLY on a different circuit :thumbsup:. Of course, it has no relationship to logic or geography.

So, I moved the plug for the AC unit from one rec to the isolated circuit (total change = 5 feet). Voila! problem solved.

Although... it is a 20 Amp circuit...

Leah Frances said:

Voila! problem solved.

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I can't stand happy endings. . .:laughing:

To OP. Sorry for the hijack.

Yoyizit said:

If you lengthen the cord to 25' you might want to go one click heavier on the cord AWG.
Whatever CB it finally lands on, you might want to alter the CB trip curve in the "time delay" direction.

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Modifying the microwave cord and plug will remove it's listing and is a direct violation. Same with your AC Leah. Your homeowners insurance would not pay the claim for this fire, should one occur anywhere in your house. Temporarily okay, but not for permanent installation. An extension cord is much better than a modified cord. It is compliant for TEMPORARY use only. I know it's hot, real hot.

Don't you worry your pretty little head, J.V. I am not extending or altering any appliance cords. Promise.

J. V. said:

An extension cord is much better than a modified cord.

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Another plug and socket doubles the contact resistance which is why I prefer a soldered splice. You do lose water resistance and some tensile strength, though, over the original cord.