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Old 28-09-2016, 13:08   #1
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Microwave Tripping Breaker

I've done some further investigating on my previously posted microwave problem. My 1600 watt microwave trips an 18 amp circuit breaker on my boat. It runs for about 10 seconds then the breaker trips. The same circuit will power an 1875 watt hair drier so I figured maybe there was a short in the microwave. I took it home and it worked fine on my houses 15 amp breaker. Any insights? Does a microwave have a "surge" in it's cycle? Is 10 seconds a "reasonable" amount of time before a breaker trips? I'm stumped.
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Old 28-09-2016, 15:01   #2
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Microwave Tripping Breaker

Bad circuit breaker? I say that as it runs fine at home on a 15 amp breaker, ergo it draws 15 amps or less.


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Old 28-09-2016, 15:10   #3
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Re: Microwave Tripping Breaker

Could be undersized conductors.

Microwave goes on, wiring gets hot, wiring resistance goes up, amperage goes up, and it pops the breaker.

(Not the most likely scenario. Bad breaker would get my first vote)
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Old 28-09-2016, 17:26   #4
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Re: Microwave Tripping Breaker

Quote:
Originally Posted by cyphert View Post
I've done some further investigating on my previously posted microwave problem. My 1600 watt microwave trips an 18 amp circuit breaker on my boat. It runs for about 10 seconds then the breaker trips. The same circuit will power an 1875 watt hair drier so I figured maybe there was a short in the microwave. I took it home and it worked fine on my houses 15 amp breaker. Any insights? Does a microwave have a "surge" in it's cycle? Is 10 seconds a "reasonable" amount of time before a breaker trips? I'm stumped.
Pure or modified sine wave inverter on the boat?
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Old 28-09-2016, 17:27   #5
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Re: Microwave Tripping Breaker

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Originally Posted by cyphert View Post
I've done some further investigating on my previously posted microwave problem. My 1600 watt microwave trips an 18 amp circuit breaker on my boat. It runs for about 10 seconds then the breaker trips. The same circuit will power an 1875 watt hair drier so I figured maybe there was a short in the microwave. I took it home and it worked fine on my houses 15 amp breaker. Any insights? Does a microwave have a "surge" in it's cycle? Is 10 seconds a "reasonable" amount of time before a breaker trips? I'm stumped.
Where did you find an 18 amp circuit breaker?

Check gauge of the wire on this circuit and use an appropriate rated breaker. 15 amp for # 14 wire or 20 amp for #12. Also, check all the connections on the circuit to make sure they are clean and tight.

I'm making an assumption of course that this is an original circuit or one installed by someone competent. It's possible that the entire run is not the same gauge or that the neutral conductor is a different gauge than the hot conductor.

If the microwave works at home but not on the boat, the problem is with the boat. If you have another 120 volt circuit on the boat, try the microwave on that circuit as a test.
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Old 28-09-2016, 17:29   #6
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Re: Microwave Tripping Breaker

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Originally Posted by jeepbluetj View Post
Could be undersized conductors.

Microwave goes on, wiring gets hot, wiring resistance goes up, amperage goes up, and it pops the breaker.

(Not the most likely scenario. Bad breaker would get my first vote)
If the resistance in a circuit goes up, the current (amperage) goes down, not up.
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Old 28-09-2016, 17:35   #7
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Re: Microwave Tripping Breaker

Not uncommon for Marine breakers to break below rating. Replace it. 1800 watt MW? Who, I thought a 1200 watter was big...
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Old 28-09-2016, 20:53   #8
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Re: Microwave Tripping Breaker

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If the resistance in a circuit goes up, the current (amperage) goes down, not up.
Indeed. I agree.

Except a microwave has a transformer to drive the magnatron. (Love the fact it's named a magnatron) - If the circuitry in the MW is trying to keep the power the same, it'll pull more current as the voltage drops (due to the resistance in the wiring)

Long shot, I know. And I've never designed a microwave, so I'm not really an expert.

If it's off an inverter, that may be an issue too as square waves don't drive transformers as well as sinewaves. (inductance and all that stuff)

The advice to replace the breaker, check the wire guage, check the connections is the best. (Guess I was bored at work...)
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Old 29-09-2016, 07:26   #9
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Re: Microwave Tripping Breaker

Thank for all the information. What stumps me is that a 1850 watt hair dryer runs fine on my 18 amp shore power circuit, the 1600 watt microwave trips the same 18 amp breaker on the boat (made in Mexico on a boat built in South Africa) but not the 15 amp breaker at home. If it's the wire on the boat or a defective breaker the hair dryer should trip the breaker. If it's a power surge on the microwave it should trip the breaker at home? Am I going to have to live with no popcorn?
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Old 29-09-2016, 07:48   #10
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Re: Microwave Tripping Breaker

Jeepbluetj may be on to something in Post #8, which is why I asked earlier what sort of inverter you have.
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Old 29-09-2016, 07:59   #11
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Re: Microwave Tripping Breaker

Inverter is easy to trouble shoot, if it works fine on shore power but not inverter, then of course inverter is suspect.


On edit, did the OP mention an inverter?
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Old 29-09-2016, 09:55   #12
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Re: Microwave Tripping Breaker

Just change the breaker to a new 15 Amp . You should carry in spares 5 , 10 , 15, etc
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Old 29-09-2016, 10:29   #13
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Re: Microwave Tripping Breaker

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Originally Posted by cyphert View Post
Thank for all the information. What stumps me is that a 1850 watt hair dryer runs fine on my 18 amp shore power circuit, the 1600 watt microwave trips the same 18 amp breaker on the boat (made in Mexico on a boat built in South Africa) but not the 15 amp breaker at home. If it's the wire on the boat or a defective breaker the hair dryer should trip the breaker. If it's a power surge on the microwave it should trip the breaker at home? Am I going to have to live with no popcorn?
A hair dryer is primarily a restive load (the heating elements)
A microwave is primarily an inductive load.

Are you using an inverter?
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Old 29-09-2016, 14:09   #14
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Re: Microwave Tripping Breaker

Was this boat originally wired for 220volt?
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Old 29-09-2016, 14:31   #15
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Re: Microwave Tripping Breaker

Indeed, the boat may have originally been 220 volt. It was built in South Africa by Admiral Yachts. I'm not sure but the wire going to the AC outlets does look small, perhaps 16 awg? If so, how would this contribute to the problem? This could explain why the unit works at home in a house wired for 120.
The issue is the same on shore power and on inverter. Runs for about 10 seconds then trips the breaker. Doubt I'd use this device much on inverter as the draw is so large but I'd sure like the microwave at the dock on shore power.
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