John Grabowski wrote:
Jeff if there is no heat as a result of a loose connection or bad contact, I
am wondering if the attic ambient temperature is a factor. Check the
disconnect's label to see if there is a mention of allowable ambient
temperature.
I've been up in the attic in the heat of summer and it really isn't
unbearable. Since the fused disconnect in question is rated for outside
service, I'd expect its inside would get hotter that the attic if it was
used outside exposed to direct sunlight, so I doubt that's a factor.
Another thing would be to check the label to see if the disconnect is rated
for the type of load that you have. Also check the nameplate on the heating
unit to see what it requires for a disconnect. It should say fuse or HACR
breaker and give an amp rating.
One other thing would be to check the connections inside of the heating unit
to make sure that they are all tight.
Have you checked starting current? Your 40 amp draw sounds like running
current. The unit probably has a much higher starting load. Also, check
the voltage when starting and running at the disconnect. If the voltage is
too low the current draw can go up.
I didn't check the voltage, but as the bulk of the load is just
resistance heaters, the current would have to be lower, not higher, if
the voltage was low, wouldn't it?
The nameplate on the air handler says 35.5 amps for the auxillary
heaters and 2.5 amps for the blower motor. that should be trivial for a
60 amp disconnect. And, if there was a huge starting surge I'd expect
the 60 amp standard fuses (they're not "lag" types) would blow. They don't.
The fuse links in the two charred fuses I replaced today were intact,
they just became unsoldered from the end caps which got heated by normal
running current levels passing through the poor switch contacts. If the
disconnect is rated for 60 amps and the 60 amp fuses don't blow, but the
switch contacts fry, there pretty much has to be something wrong with
those switch contacts, eh?
That's all I can think of.
I checked with a electrical contractors and an HVAC guy in my Rotary
Club this evening and they both said they've seen the same sort of
failures in GE fused disconnects, so I guess I have my answer, and it's
what I surmised. I'm convinced here's nothing inherently wrong with
anything else, things work just as they should for the better part of a
year and then the switch contacts start to oxidize and the problems
start. When I clean up the contacts things go back to being good until
about a year later.
I think I've about "saucered and blowed" this one now. G
Jeff
John Grabowski
http://www.mrelectrician.tv
"Jeff Wisnia" wrote in message
...
We have a 60 amp 240 volt two pole GE fused disconnect switch in our
attic supplying the air handler/auxillary electric heat for one of our
heat pump HVAC systems. It is fed from a dedicated 60 amp breaker in the
home's load center.
That switch has been a nuisance since the house was built about 19 years
ago. Every year or so the switch contacts start heating up and will
eventually heat the end carp on one of the fuses enough to melt the
solder joining the fuse's link to the cap, shutting down things. The
overheated fuse usually falls apart when I take it out, as its fiber
tube is crisped.
I take the switch apart, clean up all the discolored switch parts with a
fine file, paint some Kopper-Shield on them and put it all back together
with a new fuse. My cleaning fixups last for another year or so and the
same contact heating thing repeats.
About six years ago I gave up and figured maybe I just had a "bad"
disconnect switch, so I bought an same model GE disconnect and just
swapped in the guts to avoid having to mess around changing the housing
and cable entries. The same switch contact heating problem happened
again a year later.
The disconnect is in a dry area, and the switch is never thrown except
when I have to fix it, so why does this happen? The current draw with
the auxiliary heaters on is less than 40 amps, and as I'm using regular
quick blow cartridge fuses, I doubt if there's much surge even when
those heaters are cold, or the fuses would blow. After a cleanup I've
let the auxiliary heaters run for ten minutes and then felt the
disconnect switch parts (with the breaker off of course). They feel like
they're only a few degrees above ambient then.
Is it just that GE fused disconnects are likely to be ****e, or am I
possibly overlooking something?
Methinks I'll just pick up a non-fused disconnect and next weekend deep
six that darned fused GE disconnect I spent an hour cleaning up this
morning, when we woke up with no heat. I can't really understand why the
installers used a fused disconnect there anyway. I appreciate the need
for a disconnect in close proximity to the equipment, but having fuses
in it when it's fed from a dedicated breaker of the same rating seems
redundant. Am I right about that?
Comments?
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"As long as there are final exams, there will be prayer in public
schools"