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My block heater is tripping breakers in the house. I ohmed it out and it falls in an acceptable range. It has been a while since I did it, but I think

the reading was about 19 ohms. What ever it was, from the research I had done the reading was acceptable. 

I would think that if I had a rub thru in the wire that would give me an open reading. 

The extension cord I used to get there has been starting snowblowers and running circular saws recently with no problem.

Any ideas? Or just replace it?


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29 minutes ago, Gary L Moore said:

If I was shorted from a rub, wouldn't the circuit be open?

If the hot leg insulation of the heater power cord rubbed through on the truck body there would still be 19 ohms when tested at the plug.  If the ohm meter shows 0 ohms when the meter probes are attached to the hot led at the plug and the truck body this would be a short.   If the test shows a reading of 0L or 1 then the wire is not grounded to the body. 

An open circuit is no connection.  This is because of an open switch, a bad connection, a break in the wire, or high resistance due to corrosion. The ohm meter will show 0L or 1. 

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Check what IBM asked first.   Then:


How long is it before the circuit blows?  how warm does the extension cord get?  What is the voltage while it is plugged in?  How warm does the breaker feel?  What else is on the circuit?


the heater should pull about 7 amps.  So your thoughts on the saw etc are valid. (but we usually run the saw in bursts, not for hours)  House circuit breakers look at total Heat.  If the breaker is starting to get weak, the breaker will open at a lower temperature (lower total heat).

If your voltage while plugged in stays nearly what it was when not   (lets say 120 unplugged and 117 plugged) your cord and wiring is fine (breaker is losing its mojo).  If the plugged in voltage drops a lot, something is wrong with the cord or receptacle the cord is plugged into.




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