Voltage across 2 line feeds?

[Hamberg]

Working on a 240v (15A) circuit. Black to neutral = 121v, Red to neutral = 122v, Black to Red = 4.5v??? What am I missing - is this right? Why?

 

[JoeD]

One of the hot leads is dead.
The breaker is installed wrong and both hots are on the same leg of the service.
You used a tandem breaker instead of a two pole breaker.
Is this a new install or has it been working before?

 

[Hamberg]

One of the hot leads is dead. The breaker is installed wrong and both hots are on the same leg of the service. You used a tandem breaker instead of a two pole breaker. Is this a new install or has it been working before?

One is dead? Both have full voltage to neutral and ground. Circuit install 5 years ago and has been working fine.

Circuit background: 240v/15A 2-pole breaker servicing two heated floors/thermostats.

One stat died and was just following trouble shooting procedure.

 

[kok328]

Are you taking these reading from the breaker or from the end of the wires?
Is your meter on the correct setting for measuring 240V ?

 

[Hamberg]

Are you taking these reading from the breaker or from the end of the wires?
Is your meter on the correct setting for measuring 240V ?

end of circuit. MM set at 200v~

I'm missing something here...

 

[Eddie_T]

I would also check voltages at the breakers.

 

[kok328]

I would also check voltages at the breakers.

and set your meter above 200v, your measuring 240v

 

[afjes_2016]

.

Hamberg: Yes as advised take your readings at the breaker itself first. Start at the beginning first.
If the readings are correct at the breaker then go to the next point of connection and take your readings there.

If one stat died and you are taking readings after that stat this may be the reasoning of no 240v. I'm wondering why a neutral is in play though. I am not that familiar with floor heating so maybe it is a 120/240v circuit.

.

 

[jmg1213]

Yes, first check at the breaker box. If you have the same reading there, then going back to the first answer double check to make sure the two lines are not coming off of the same leg at the breaker. The black wire should be on one leg and the red wire on the other leg in order to get 240v.

 

[Hamberg]

and set your meter above 200v, your measuring 240v

each pole is only 120v, right?

 

[Hamberg]

I would also check voltages at the breakers.

Breaker voltage is good. pole1 (black) = 122.3 to neutral & ground. pole2 (red) = 121.7 to neutral & ground.

4.6v across red/black

 

[Hamberg]

Hamberg: Yes as advised take your readings at the breaker itself first. Start at the beginning first.
If the readings are correct at the breaker then go to the next point of connection and take your readings there.
If one stat died and you are taking readings after that stat this may be the reasoning of no 240v. I'm wondering why a neutral is in play though. I am not that familiar with floor heating so maybe it is a 120/240v circuit.

Here is the wiring diagram. There is a junction box in the basement, I'll check connections there too.

One floor was installed in 2016 and the other in 2017 - working fine since...

 

[kok328]

each pole is only 120v, right?

yes and you indicated that you meter is set for 200V range, so your meter can not measure between black and red. set the meter higher and recheck the breaker.

 

[kok328]

.

Hamberg: Yes as advised take your readings at the breaker itself first. Start at the beginning first.
If the readings are correct at the breaker then go to the next point of connection and take your readings there.

If one stat died and you are taking readings after that stat this may be the reasoning of no 240v. I'm wondering why a neutral is in play though. I am not that familiar with floor heating so maybe it is a 120/240v circuit.

.

There is no neutral in this setup.

 

[Hamberg]

yes and you indicated that you meter is set for 200V range, so your meter can not measure between black and red. set the meter higher and recheck the breaker.

One of those moments!

 

[Hamberg]

There is no neutral in this setup.

Something I should have mentioned... Circuit is on a sub panel. Circuit is 14/3 and you are correct the diagram shows to ground NOT neutral. It is "currently" wired to the neutral.

 

[Eddie_T]

You should have 240v at the breaker. If you only have 4.6v I would check another 240v breaker just for a sanity check. If one side of the breaker is faulty the voltage could just be thermostat feedback. BTW is the other mat heating properly as you troubleshoot this thermostat?

 

[Hamberg]

Fixed!! (as always!) Thanks for the help/suggestions. Pulled cover off of junction box, pulled wire nuts off and one of the feed wires was not fully engaged.

No idea why it has taken 5 plus years for it to work itself loose but (re)wire-nutted the feeds and we are back up and running!

BTW, not sure who the inventor of heated flooring was/is but I'd nominate them for a Nobel prize!

 

[Hamberg]

There is no neutral in this setup.

So, follow up to @kok328 's comment...

If this ok with the Stat ground going to the neutral or should it come apart, cap the neutral and reconnect to ground?

 

[kok328]

You should have 240v at the breaker. If you only have 4.6v I would check another 240v breaker just for a sanity check. If one side of the breaker is faulty the voltage could just be thermostat feedback. BTW is the other mat heating properly as you troubleshoot this thermostat?

check all you want. until the MM is set correctly you won't get 240V of any 2 pole breaker.