Inconsistent House Wiring Failure

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Old 01-04-10, 01:10 PM
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Question Inconsistent House Wiring Failure

My son has garage wiring outlet that drops by 20 volts, 121 to 101, when a 1-HP air compressor with 3 gal tank is started up. The compressor seems to run at a reduced power (speed?) for a few seconds, then at full power for a few seconds, and then trips the breaker switch. During all of this time the voltage is down about 20 volts. Nothing else; hair dryer, freezer, vacuum cleaner, will cause the garage wiring breaker to trip and the voltage is only dropped by about 2 volts. But, when the air compressor is plugged into an outlet inside of the house it runs fine, the breaker is not tripped, wand the voltage drops about 3 volts. This compressor had been used and OK at previous house as well. All lines involved are on 15-20 Amp 120 Volt.

I would appreciate any comment. This is the strangest thing I have ever seen.
 
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Old 01-04-10, 01:18 PM
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A couple things come to mind here as potential problems:

1) The garage circuit is a long way from the panel, maybe more than 80'? I am assuming attached garage -- if detached please specify as this could open up different problems.

2) There is a weak connection in the circuit like a backstabbed receptacle, loose wirenut, bad cord, etc.

3) The breaker for this circuit is not securely fastened in the panel -- perhaps it's damaged by heat or arcing or not the correct brand.

In any case, you shouldn't run the compressor on this circuit until the problem is fixed. It will eventually ruin the motor.
 
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Old 01-04-10, 01:53 PM
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Compressors are happier on 20 amp 12 gauge wire circuits with a new electrical outlet which firmly grips the prongs on the plug!

And same with a long smaller gauge extension cord, say 50 ft. Try plugging that into the house outlet which works, then the compressor into the extension cord, and the compressor may not work well.

Basically for longer distances, use larger gauge wire.

Voltage drop calculator...
Google
 
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Old 01-04-10, 02:22 PM
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Question Inconsistent House Wiring Failure

Ben and Bill, thanks for your inputs.

The garage is attached and the garage outlets are near the breaker box which is on garage wall. Both garage outlets, one within 5 feet and one about 25 feet away, show same failure. The outlet that is indoors is further away by about another ten feet.

The breaker switch looks OK on the surface and appears to be in place just as the others. It is same brand as others, which appear to be original to this 5 year old house. It has not been pulled out as yet.

I agree that running on this circuit could damage compressor as well as any other motor type appliance also on the line. Thanks for that warning.

The voltage was monitored with a little portable multi-meter going to another outlet on same wiring line. The same extension cord, 3 wire 14 gauge, about 25 ft., was used for all plug-ins including the other appliances. Trying a longer extension cord for the in house plug-in is a good idea and will be tried.

Any more ideas?
 
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Old 01-04-10, 02:47 PM
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garage outlets are near the breaker box
To expand on what Bill 190 said since it is easy to install a new 20a dedicated circuit for the compressor do that and get rid of that extension cord. No, not a fix for the receptacle but a better way to run your compressor. Good suggestions have been offered for what problems to look for to fix the receptacle. Do voltage checks when troubleshooting with something like an electric heater not the compressor. Heater won't be damaged, the compressor might be.
 
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Old 01-07-10, 02:52 PM
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Inconsistent House Wiring Failure

Thanks for all the good ideas. I wish garages came with more outlets. Guys are really being shortchanged by the builders. Indoors there are outlets everywhere. We should be marching in the streets.

However, mystery still is a mystery. If I had a scope Id like to check waveform to see if something looks funny. Also like to get a meter to measure current. Wish power company provided them. I will post again when I learn more. Any more ideas are welcome.
 
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