Question sent as the result of the feedback form.
It was submitted on Tuesday, December 26, 2000 at 20:18:07
By Robert Stewart of Austin, tx.
Brand: Coleman Evcon
fuel: electricity
location: closet
problem: intermittent
The problem that I keep having, is the buss fuses
keep blowing out. We had it repaired, or we thought so. They replaced a
transformer and said it was fixed. Now the heater just went out again this
time the fuses caught on fire, and burned a couple of wires. I do know
that it can be rewired, but my question to you is why does the fuses keep
blowing out, not only do they blow but they are also really hot to the
touch.
From: Scott Meenen n3sjh: It sounds like you have
the wrong size fuses or a problem with dirty or crummy connections on the
fuses and holders causing both to over heat and fortunatly the fuses will
blow to protect the equipment from fire (you hope). Loose connections cause
as much if not more problems than short circuits. I would suggest buying
or borrowing a clamp on ammeter and checking the current draw on the heaters.
Unless the heaters are shorting to the case of the cabinet they should
draw the same or less of their rated current. The rule of thumb for fuses,
circuit breakers and wiring is to load within 80% of the rating of the
wiring and the fuses should blow when over loaded to 125% (the reciprocal
of 80) of the circuit capacity. A 5kw heat strip will draw 21 amps at 240
volts and 16 amps at 208 volts. Following the rule you need a 30 amp circuit
for the 21 amp load.
Example a 12 gauge wire normally can handle 20 amps
that means you should have no more than 16 amp flowing through it and when
you get to 25 amps the 20 amp fuses or circuit breakers should blow. This
does not mean that you should run 20 amps even though the wire can handle
it and the fuses or breakers may not blow. This margin is to allow surges
for motors and other starting currents.
Scott.
Definitions:
Blower: usually a squirrel cage centrifugal air moving device. Will move
large volumes of air relatively quiet. Will use less energy with more back
pressure.
Fan: a paddle type air moving device used where noise is not a major consideration.
Will use more energy with more back pressure.
Combustion blower: A blower used on high efficiency furnaces or oil burners
to move combustion air. usually 1/20 to 1/6 horsepower.
OEM: Original equipment manufacturer.
Horsepower: 746 watts
KW Kilowatt (1000 watts) or 3400 BTUs per hour
RPM: revolutions per minute.
Service factor: the extent to which a motor can be safely overloaded beyond
its name plate ratting without over heating.
Air over horsepower: The rating of a motor assuming air flow through the
windings usually as a result of the air moving device.
SAE: Society of Automotive Engineers.
Ton 12,000 BTUs per hour of heating or cooling
This page will be updated soon
Good Luck Scott
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ice outside in the heat mode click
here.
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up
in the cooling mode click
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Any other questions feel free to contact us by
any of the means below. good luck Scott.
Written By: Scott
Meenen N3SJH of: G&S MECHANICAL SERVICES. Specializing in Mechanical, Controls
and Electrical Modifications Of
Heating, Air-conditioning, Refrigeration,
Cold storage,
Ice Production and Food preservation.
Anything having to do with Heat and Energy.
Serving MD, DC, and Northern
VA. Contact us by pager: 1-877-467-2914