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cyphert · 24-09-2016, 12:31

I've been trying to run a 1600 watt microwave off shore power. I plug it alone into an AC outlet and it runs for about 20 seconds then trips the 18 amp circuit breaker. Since 1600/120 = 13.3, I thought it should not do this. What am I missing?

Paul L · 24-09-2016, 12:42

Check the rated power consumption wattage. The 1600 watts is power to the food.

cyphert · 24-09-2016, 12:44

I did. This is the "input" power.

**GordMay** · 24-09-2016, 12:47

Are you actually getting 120VAC to the boat?

**a64pilot** · 24-09-2016, 13:17

I'm not sure I have ever seen an 18 amp breaker?
Which breaker is it that is tripping, the main shore power one?

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cyphert · 24-09-2016, 13:21

Yes. I've read the correct formula when calculating amps in an AC circuit is I = W/VxPF so maybe if the power factor was say 0.6 then I would actually be drawing 22 amps? Now, I'm wondering if the wire size in my AC circuit will allow me to use a higher amp circuit breaker?

cyphert · 24-09-2016, 13:44

No, it's not tripping the main shore power circuit. It's tripping the breaker labeled AC outlets i.e. the various AC plugs onboard. The boat is an Admiral 38 catamaran built in R.S.A. and occasionally I find some stuff generic to South Africa.

**StuM** · 24-09-2016, 15:19

Quote:

Originally Posted by cyphert

Yes. I've read the correct formula when calculating amps in an AC circuit is I = W/VxPF so maybe if the power factor was say 0.6 then I would actually be drawing 22 amps?

You're probably correct. Here's a real world test:

"We recently checked a typical microwave oven. The glossy label advertised the output power to be 800W. The compliance specification label read 1150W. When run off a Selectronic SA22 Sine Wave inverter, the current draw on the DC side was 70A @ 24V or 1680W - more than double the advertised 'output power'."
(bold emphasis added)
Power Consumption of Cooking Appliances | Don't cook your inverter

CaptTom · 25-09-2016, 05:57

Two dumb questions popped into my mind (sorry):

1) Why a 1600W microwave? We use a 750W on the boat. Cheap to buy, cheap to replace, and runs great on the inverter. I don't think the "big" one at home is more than 1250W, and we never wished we had more.

2) Bad breaker? If you can't find a replacement, is there any way to swap it for another one from the same panel?

For troubleshooting, if you don't have the proper meters, plug in a 1500W space heater. If that trips the breaker, you know which way to proceed.

belizesailor · 25-09-2016, 06:17

Labeled power ratings are often way off from actual (as shown in Stu's post). Only way to know for sure is to break out the multimeter and test it. Test actual voltage you are getting at the device and actual amps draw (a clamp on will make this much easier).

**GordMay** · 26-09-2016, 05:10

A "line splitter" makes testing appliance current with a clamp meter easier.
➥ http://www.itm.com/pdfs/cache/www.it...-datasheet.pdf

**a64pilot** · 26-09-2016, 05:45

18 amps X 120VAC = 2,160 watts.
I doubt the thing is pulling that much, as vast majority of US household circuits are 15 amp, that is 1800 watts.
Why would anyone manufacture something that would blow the CB on almost all homes?

I'm betting a bad CB