bad phase

[littlewing78]

working in a an apartment complex ant we have single phase 120/240. the problem is that in all the apartment i read 120 on bothe phases but zero from phase to phase. one phase is good and one is bad. on the bad phase i read 120 but when i plug something in on a branch circuit of that phase i get a voltage drop, and whatever i plug in doesnt work. it acts like a series circuit some how. power and the main is correct though. does any one have a clue what this could be?

 

[al hildenbrand]

Re: bad phase

The voltage that you are detecting on the "bad phase" is the voltage of the "good phase" seen through a 240 volt load. The resistance of that load added to the load that you plug in form a voltage divider, so you see the voltage drop.

Sounds like the "bad phase" has an open in it. Follow the voltage from the panel until it disappears.

 

[hurk27]

Re: bad phase

Turn off all two-pole breakers to the 240 volt appliances, Water heaters,dryers,ranges, anything that uses 240 volts. this will allow you to follow to the point where the loss is. If there is a fusable main disconnect this would be the first place to check. then check for voltage to neutral at each point of connection.