HaHaHa wrote:
From: Jeff Wisnia
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
Jeff, any particular reason the disco is fused?
You'd have to ask the original installer. I was too busy making sure
lots of other stuff got done OK while the place was being built and
didn't stop to question why it was fused then. I'd already agreed to the
overall price of the HVAC system, so questioning why it needed fuses
wouldn't have made any price difference anyway. G
Fuses there never made much engineering sense to me though.
But, a couple of others on this thread have raised questions about
whether the equipment manufacturer may have particular requirements
about the line feeding it being protected by fuses rather than just a
breaker. I can't think of any technical reason for that requirement for
a piece of equipment which is principally just a 1/4 hp fan motor with
occassionally a 35.5 amp resistive heater load added to it.
Usually, fused disconnects are redundant. Having a disco within sight of the
equipment is required, but to include overcurrent protection twice (once at the
main panel, and again at the disco) seems silly.
Or replace with a simple, 2-pole circuit-breaker disconnect.
I kinda thought that "simple is better" that's why yesterday I bought
what looks like a simple and robust 60 amp Square-D "plug disconnect"
which I'll probably swap in this weekend.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"As long as there are final exams, there will be prayer in public
schools"