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
but when the motoer and iginition transformer were added to the load the
dropped and the relay dropped out. This cycle repeated itself over and over
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
in a web page, and is free
as are the other 24 electrical calculators at my site:
Well, my 21 year old home has a conventional breaker panel, but the HVAC
equipment (2 heat pump systems) was installed with a total of four fused
disconnect switches located near the compressor and air handler units to
provide appropriate safety disconnecting means for service people.
Those disconnects were fitted with cartridge fuses of exactly the same
amperage as the panel breakers which protected the dedicated lines
feeding them, so the fuses inside them were redundant, 'eh?
The reason I'm mentioning this is that one of those fused disconnects, a
60 amp GE unit adjacent to our attic mounted air handler with auxillary
strip heaters in it, has given me trouble with fuse failures about once
every couple of years.
The fuses didn't "blow" in the conventional sense, what happened is that
the closed switch contacts oxidized to the point where they developed
enough resistance to generate significant heat when the 40 amp strip
heaters were drawing current. After a while the end cap on one of the
fuses adjacent to that switch contact became heated enough so that the
fibre fuse body would char and the solder holding the fuse link to the
end cap melted, "opening" the fuse, but leaving the entire fuse link
still intact and "unblown".
I'd clean up the switch contacts and fuse clip and install a new fuse
and things would be OK for another couple of years and then the same
damn problem would occur. About ten years ago I bought and swapped in a
whole new identical model GE fused disconnect only to find the same
problem occured a couple of years later.
A fuse "charred out" again last week, so over the weekend I bought a
Square-D 60 amp UNFUSED disconnect and replaced the fused one with it.
I'm hoping the "plug and socket" contacts in the new disconnect will
fare better than the switch contacts in the old disconnect. I put my old
Simpson 260 meter across them with the strip heaters running and
couldn't see any movement of the meter pointer on the 2.5 vac scale, so
I know they're making good contact now, I just hope they stay that way. <G>
The first thing I tried, when the first fuse "fried" that way, was to
brush a little Thomas & Betts "Koppershield" on the switch contact
surfaces and on the cartridge fuse clips themselves.
That may have helped, but it didn't stop it from happening over and over
again every couple of years.
I've mentioned the problem to several experienced electricians and they
all said they've seen the same problems occur in GE fused disconnect
I suspect that the first time the overheating happens the heat anneals
the copper swich blades and or the springs which apply pressure so they
are no longer stiff enough to maintain a low resistance contact.
Whatever, nuttin's perfect is it?
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