Bizarre one - 240V turned into 120V

Hi real weird one here, troubleshooting a 240V hot water heater problem, stopped working, checked voltage and guess what, BOTH legs going to heater are the SAME phase 120V! WTF? What's in the FP panel box is a 2 pole FP tandem breaker that probably has been in there for 40 years, box NEVER opened! HOW COULD THIS HAPPEN? Anyone have any explanation for this?

 

Welcome to the forums!

To be clear, you have 120 volts between the two hots, correct? What do you have from each hot to ground? By FP do you mean FPE?

 

Is it 2-pole or tandem? If it is tandem it is two 120 circuits and isn't 240.

 

It is an old 2 pole Federal Pacific 20amp Breaker. It SHOULD have 240V between the two legs but right now it has 0V between the two legs because inexplicably they are now the same phase! Each one reads 110V but that doesn't do me any good! Could a circuit breaker malfunction in this manner? Doesn't seem possible!

 

Possibly the breaker isn't in the right location. If it is a 2 pole breaker then it has two snap on conductive feet. One needs to be on each leg.

 

If no changes have been made to your electrical system you may have lost a phase. Turn off all your two pole breakers except the main breaker and see if other circuits turn off. If so, you have lost a phase and need to call the power company 24/7 service line.

 

Your reading would be explained if it really was a tandem breaker as you first wrote not a 2-pole breaker. Are the handles connected together?

 

You have single phase power so you haven't lost a phase, but you could have lost a leg. IF you have 240 volts across the two legs at the main breaker you probably have a bad 30 amp breaker for the water heater and you are reading the same leg as it feeds trough the elements. IF you don't read 240 volts across the main breaker and read nothing, you probably have lost a leg ahead of the panel as Tolyn mentioned.

The thin series of FPE breakers are a Type NC.

http://www.amazon.com/FEDERAL-PACIFI.../dp/B00822ECZC

 

Phase...leg...whatever. Tomato...tomahto.

 

If the circuit breaker became defective it could be sending the same leg through both hots to the water heater- or be sending one leg and you have a short somewhere between the circuit breaker and the water heater. It would be strange if you lost a leg here, because if that were the case I would expect that you would get 110-120 on one of your hot wires and 0 on the other (unless something is defective and sending power back into the dead leg). If you have lost a leg it may or may not be on the electric company, as you may have lost it between your circuit breaker box and the meter, in which case I would think that it is going to be your responsibility to repair. If there is no cutoff you will need to have them disconnect your service at the pole or pull the meter (I like to have it disconnected at the pole, then install a cutoff switch at the same time. If you have lost a leg it will be difficult to tell if its before or after the meter, so I think that you will need to call the electric company for help regardless (I would think that newer meters can tell if something is no longer hot from the pole and send a message to HQ, but I don't know about that really...) At any rate my best regards.

 

Actually, what he's seeing is quite common because the second phase is being back fed through some other 240 V appliance in the home.