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John G

pretended :
I was called today to assist the burner repair guy with an electrical
problem in one of the apartment houses I work in. He wasn't able to get
correct voltages at one of the zone valves.

I heat my home entirely with wood, so first let me say that what I know about
heating systems could fit into a very small vessel. But I offered my
assistance as an electronics technician.

There was a bank of 24 volt transformers, each feeding two apartment's zone
valves. And two of these apartments had no heat. He told me that the
transformer was a 40 volt unit, he went on to say that it was good, and
attempted to demonstrate this by measuring across each secondary terminal and
ground. When doing this he measured 40 volts from each secondary screw to
building ground. I had to look twice at this to believe it. There was indeed
from each screw to ground 40 volts!

So my next best guess was that perhaps it is a 40 volt unit and with a center
tap to case ground. So half expecting to see 80 volts across the secondary I
read 0 volts. However I did confirm the rating on the label. It was a 24 volt
non tapped transformer and an ohm meter check between each secondary terminal
and ground showed infinity. And interestingly the same check across the two
secondary terminals showed 1 ohm.

We replaced the transformer with a new 24 volt unit and restored the heat in
the two apartments. I asked for the transformer. I may have a chance to
autopsy it after the guy shows it to his boss. Whether I'll notice anything
would remain to be seen.

This problem seems to defy all logic. Does anyone have any thoughts as to
what could be going on here? Lenny

What did you measure the 40 volts with ? Digital volt meter I suppose.
Why did the Tech (Electrical?) tell you they were 40 volt units when
the label said 24 volts?

Since end to end of secondry is 1 ohm, of course the volts to ground
will be the same both ends. :-?
It is most likely the primary is open and all the volts are just
coupling from the line to the secondry.
You did not tell us the continuity of the primary. :-?

--
John G