Never saw this before

[hbiss]

I just watched a You Tube video by a plumber who was troubleshooting some thermostat and zone valve problems. He found a dead short on the wiring off the 24vac control transformer which blew the internal fuse. So, he replaced it and in doing so checked for 24v on the secondary screws to see that it was working. But what I never saw anybody do is measure from each side of the secondary to ground, noting that one side is higher than the other and call the higher side the "hot" and the other "common". He actually marked H and C on the transformer with a Sharpie.

I submit that any voltage to ground is a phantom of his DVM since the secondary is floating. Secondly, what does it matter?? There is no reason for a H and C.

-Hal

 

[Dsg319]

Don’t know why he would mark it like that. As you said the floating secondary voltages to ground are meaningless

 

[qcroanoke]

It's been a long time since I seen a control xfmr secondary that one side wasn't grounded.
In hvac units anyway.....

 

[LarryFine]

It's been a long time since I seen a control xfmr secondary that one side wasn't grounded.
In hvac units anyway.....

Yes, they do that now, but not internally within the transformer itself.

 

[ptonsparky]

Wow, learned something new today.
Because of flame detection? Ignition.

 

[LarryFine]

I believe it's more because of electronic thermostats that the 'common' leaves the AHU.

 

[CoolWill]

It's because he is a plumber.

 

[Eddie702]

On most furnaces the ignition and flame sensing the current is returned to the ignition module via the metal on the furnace so that is one reason one side of the transformer is grounded