24v bonded on secondary side of x-fmr

[wdalrymple]

I was helping our hvac guy to track down why his control voltage transformer was frying. noticed the secondary side one line was bonded tothe frame of the hvac equipment which was bonded to the equipment grounding conductor. he stated this was how he found it. so we hooked up another x-fmr. it also blew. we took the ground off and the next one held. is the secondary side supposed to be bonded or not.

 

[iwire]

Re: 24v bonded on secondary side of x-fmr

It can be, and having it bonded can make troubleshooting easer.

What you describe sounds like you have a ground fault of what used to be the ungrounded 24 volt conductor.

You really did not fix the cause of the problem you changed the way the circuit was wired.

 

[hbiss]

Re: 24v bonded on secondary side of x-fmr

No, but I can't see why there would be a problem if it were. Nothing is supposed to get back to ground. Probably a ground fault somewhere and by bonding one side of the transformer current is flowing through it.

-Hal

 

[don_resqcapt19]

Re: 24v bonded on secondary side of x-fmr

If the power supply to the AC unit is from an ungrounded system or if the supply power exceeds 150 volts to ground, then the secondary of the control power trasformer is required to be grounded. 250.20(A).
Don