[firefishq]

need help trouble shooting electrical supply to a/c unit. I have a 240 system. At the fuse box I have to supply wires and am getting 121v on one side but only 55v on the other. I have 240 at the breaker and just replaced the breaker. When I wiggle the supply wire on the low side the voltage changes anywhere from 35v to 60v.

thanks

 

[jbfan]

You have a bad connection on the buss, or you have lost a leg. Check the voltage on the incoming breaker and on the buss.
Call the power company if you do not have 240 across the breaker.

 

[Missouri Bound]

I have 240 at the breaker and just replaced the breaker. When I wiggle the supply wire on the low side the voltage changes anywhere from 35v to 60v.

thanks

Turn off the breaker and switch the wires.
If the problem moves you have a bad wire or bad connection
You have 240 volts at the breaker? In the circuit breaker panel or at the disconnect for the HVAC unit?
Where are you "wiggling" the wire....in the panel, at the HVAC disconnect....or at the unit itself?

 

[surferdude2]

I'm not sure of the area you are getting the low voltage measurement from. You say you are measuring 240 volts at the breaker but at the fuse box one side measures 121 volts and the other one 55 volts and it varies when you wiggle the wire. Is that "fuse box" a fused disconnect at the AC location? If so, it sound like the wire may be loose or the terminal may be burned and corroded. If so, turn the breaker off and break the disconnect connections down for inspection and possible cleaning/repairing as need be.

If instead you are wiggling a wire at the main panel, post back that clarification and be careful in there since the energy level is high enough to do severe harm if you slip up.

 

[firefishq]

I have 240 v at the breaker in the circuit breaker panel. the wire that I was wiggling was at the the fused disconnect at the AC location. BTW, I disconnected the wire on the low side and checked the voltage directly on the wire and the voltage remained low @ 55 v.

 

[surferdude2]

I have 240 v at the breaker in the circuit breaker panel. the wire that I was wiggling was at the the fused disconnect at the AC location. BTW, I disconnected the wire on the low side and checked the voltage directly on the wire and the voltage remained low @ 55 v.

Bad connection at some intermediate junction or a damaged conductor... either one will be fun to locate. First... double check that the wires are making good contact at the breaker... you may have measured from the terminal and not the wire when you got that 240 volt reading.

Wiggling the wire at the disconnect and getting a change make you think the trouble is nearby???

 

[Missouri Bound]

I disconnected the wire on the low side and checked the voltage directly on the wire and the voltage remained low @ 55 v.

Directly on the wire.....where?
Let me backtrack. If you disconnect the wire at the breaker (both wires) you get 240 across the breaker and 120v at each half to neutral....is that correct.
But if you disconnect the wire at the _________(fill in the blank) you get 55V.
It looks like you are narrowing it down a bit....to either a problem with the disconnect or a bad/broken wire.

 

[bfrabel]

Look for a junction box somewhere between the breaker and the disconnect. Perhaps on the other side of the wall from where the air conditioner is.

Shut off the breaker, open that box and check for loose wire nuts.

 

[firefishq]

I removed the wire from the terminal at the disconnect. The voltage whether connected or not was @ 55v. it did vary a bit when it was connected to the terminal when I wiggled the wire.

 

[Oldmaster]

At the disconnect are you measuring the top or bottom terminals.

 

[chetwisner]

Measure voltage across the breaker, with wire disconnected: probes on each terminal. What's the voltage?

Measure from one terminal to neutral, then from the other to neutral. What are the voltages?

 

[seharper]

The 55V is just phantom voltage. It's just induced (capacitive coupling from adjacent wires). This means it's disconnected, either at the breaker or between the breaker and the disconnect.

One reason Missouri Bound wants you to swap the wires on the breaker, is to force you to re-make those connections. It might be loose on a breaker, and you're getting 240V across the lug screws but the wire isn't seeing it etc.