Can a 240volt circuit have bad polarity?

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Sparky7762

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A friend of mine has an RV which requires 240volts to run his Air Conditioner. This plug has indicator lights on it which tell whether or not the circuit is good. When he has it plugged into a dedicated circuit for his RV, the lights show "Bad Polarity". When he plugs into an RV Park everything works fine. I have checked the two legs and get 120v on both of them, and 240volts between them. What am I missing?
 
Only thing I can think of is open ground.


Also what type of plug is this? I am not aware of AC units having plugs indicating polarity.
 
Sparky7762 said:
A friend of mine has an RV which requires 240volts to run his Air Conditioner. This plug has indicator lights on it which tell whether or not the circuit is good. When he has it plugged into a dedicated circuit for his RV, the lights show "Bad Polarity". When he plugs into an RV Park everything works fine. I have checked the two legs and get 120v on both of them, and 240volts between them. What am I missing?
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I agree do not only check line to line and line to neutral check line to equipment ground and nuetral to equipment ground.
 
I agree that is sound like a neutral or ground issue.

I doubt the A/C requires 240 volts. I have never seen an RV with 240 volt appliances. Everything is 120 volts so they can run on smaller 120 volts circuits in a limited mode. The 50 amp 120/240 supply simply gives the RV the equivalent of 100 amp 120 volts supply.
 
Sparky7762 said:
A friend of mine has an RV which requires 240volts to run his Air Conditioner. This plug has indicator lights on it which tell whether or not the circuit is good. When he has it plugged into a dedicated circuit for his RV, the lights show "Bad Polarity". When he plugs into an RV Park everything works fine. I have checked the two legs and get 120v on both of them, and 240volts between them. What am I missing?
Click to expand...

RV's can be quite a challenge. There should be a book for that system which is reporting "Bad Polarity". In it should be an explanation of what possible situations are producing that result.
 
Sparky7762 said:
A friend of mine has an RV which requires 240volts to run his Air Conditioner. This plug has indicator lights on it which tell whether or not the circuit is good. When he has it plugged into a dedicated circuit for his RV, the lights show "Bad Polarity". When he plugs into an RV Park everything works fine. I have checked the two legs and get 120v on both of them, and 240volts between them. What am I missing?
Click to expand...

RV's don't have 240V air conditioners, everything is 120V. That way, if they get to a park that only has 30A 120V receptacles available, they can use an adapter (50A 120/240 to 30A 120V) so they can still have power.
 
Sparky7762 said:
A friend of mine has an RV which requires 240volts to run his Air Conditioner. This plug has indicator lights on it which tell whether or not the circuit is good. When he has it plugged into a dedicated circuit for his RV, the lights show "Bad Polarity". When he plugs into an RV Park everything works fine. I have checked the two legs and get 120v on both of them, and 240volts between them. What am I missing?
Click to expand...

I'd pull the receptacle and confirm that one of the hots and neutral aren't swapped.
 
sparkyrick said:
I'd pull the receptacle and confirm that one of the hots and neutral aren't swapped.
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What he said. If all you did was check line to neutral voltages you wouldn't have seen the problem if there were a hot and neutral reversed.If you check line to line and get 120V instead of 240V, there's your problem.

240V appliances are polarity agnostic but 120V devices are not.
 
If you had an ungrounded and the neutral reversed at the receptacle - that would leave you with 120 volts on one side, but would leave you with 240 volts on the other side.

Unless the onboard power system is capable of detecting this and locks things out you will supply 240 volts to loads only intended to run on 120.
 
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