My neighbors had asked me to take a look at the air compressor saying it didn't work. It turned out that their 240V outlet might be at fault. In the outlet, I measured about 120V between one hot wire and the ground and around 55V between the ground and the other hot wire. How can this be and what is wrong here? Thanks for any conment or suggestion. Best wishes, h.

Bad connection/broken wire in the outlet box or possibly a bad breaker. Should measure 120-120 /240 between both hots.

The outlet itself may need replacing. Its not uncommon that older outlets fault after years of use creating a bad connection. I would not recommend plugging anything else into it as it can cause damage to some equipment.

@harum -

Firstly, verify the volt meter you are using is working properly on a known 240V (nominal) circuit. If this is the case then chances are you have either a bad plug or one leg of your branch circuit has come loose back at the panel.

Secondly, find the circuit breaker that supplies power to this receptacle in question and verify at the source that you have 240V (nominal) between legs at the circuit breaker... if you get the same reading back at the circuit breaker then you can begin to worry... as a leg in your panel might have been dropped or come loose somewhere. If you get 240V at the panel and not at the receptacle then you have found the problem.

Hope this is helpful.