My bother-in-law called and said his furnace was off again after he was
billed $240 by the local repair shop. I called the repair shop but they
wouldn't come again until the bill was paid. I said that the bill shouldn't
be paid until the furnace works. So I took my tools and meter to town and
began trouble shooting.
A relay in the fire eye control for the oil burner chattered every time we
tried to start the burner. Well, this was easy, I replaced the control.
Turned it on and it chattered again. I checked the voltage at the switch,
it read 108 volts. I checked the voltage at the panel - 108 volts from A to
neutral and 120 volts from B to neutral, and 0 volts from A to B. What the
hell, I thought. Something is weird here. The burner breaker was on A bus
so I changed it to B bus and the burner took off. I next went to the
service. And guess what I found? A fifty year old service panel with two
60 ampere fuses and the one on A phase was open.
Apparently, the hot water heater that was on 240 volts was allowing B phase
to back feed into the neutral through A phase loads setting up a voltage
divider. When the burner was first turned on the relay got 108 volts and
pulled in,
but when the motoer and iginition transformer were added to the load the
voltage
dropped and the relay dropped out. This cycle repeated itself over and over
causing
the relay to chatter. I asked my brother-in-law if he had any hot water and
he said not
since the furnace went off. Hey, this is what I should have asked before I
spent $80 for a new controller. I asked if some of the lights had been
dimming at times. Oh yes, he said. Again, I should have asked that too.
But mainly, I should have looked at the service. Who would think a house
would have fuses this day and age?
As for the service repair shop - well I asked my brother in law if the hot
water went off after the repairman was there and he said yes, and that his
brother who had been staying in the basement was using some electric heaters
to get warm. Darn residential work, it will get you every time.
By the way, if any of you are looking for a dwelling range calculator per
2005 NEC Section 220.55
I just finished one. It took about 3 weeks to write in JavaScript and runs
in a web page, and is free
as are the other 24 electrical calculators at my site:
http://www.electrician2.com