wrote in message
...

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





I would hazard a guess that the secondary winding had shorted into the
primary winding.


Gareth.