The Neutral had a tight connection, as did the other circuit Neutral and
the 50A Al feed Neutral.
The dust collector has a dedicated line because of my concern about its
18A pull on the 20A breaker. The planer is on the remaining 120V
circuit from the subpanel, the Neutral wire of which shows no damage.
Your rationale about the apparent unbalanced current draw on the Hot and
Neutral lines seems well founded. However, it also assumes that the
underlying problem was with that circuit.
Based on my own subsequent analysis and that of others on the
rec.woodworking group, I now believe that the underlying problem was the
connection of the Al 50A feed Neutral to the bus bar. I now believe
that the connector problem - well known with Al wire - caused the bus
bar to overheat (remember, the plastic around the bar shows signs of
melting) and that caused the insulation on the dust collector neutral
wire to char - because - I now assume - the insulation was probably in
contact with the neutral bus bar. Neither the feed Al line or the other
120V neutral line have their insulation within 1/4 inch of the bar.
This is conjecture at this point, but does seem to address all of the
observations and known facts.
CDW
John Grabowski wrote:
I am also puzzled by the neutral conductor burning, but not the hot
conductor. Assuming the neutral had a tight connection it indicates to me
that the neutral was carrying more current than the hot. This would only be
possible if the neutral conductor is shared by another circuit which is also
on the same phase as the dust collector. Is it possible that your planer is
on the same phase as the dust collector and their respective receptacles
share a common neutral?
"Seawulf" wrote in message
news:5xIWd.113248$JZ2.87587@fed1read02...
John Grabowski wrote:
I'm guessing that the 12-2 romex is too small for the 18 amp load. The
nameplate reads 120volt/18amps but in reality it's possible that your
voltage is only 110 or 115 with a load on. In that case your motor will
draw more than 18 amps. The neutral connection may have also been a
little
loose to cause the charring.
The dust collector should have been wired with a 30 amp circuit or
changed
to operate at 220 volts.
I get your point. But, if the charring of the insulation on the
respective Neutral wire was due to an over-Amperage, (i.e. enough to
create sufficient heat for sufficient time)I would expect the breaker to
trip. Of course, that assumes the breaker actually trips IAW spec -
which I do NOT know to be the case.
Someone else suggested that a more-or-less continuous operation of the
dust collector, would, itself, require a de-rating of the cable
amperage load spec and, as you suggest, moving to a 10 gauge cable.
But, in fact, the dust collector runs very intermittently. I usually
have it connected to my small 13 inch thickness planer, which is rarely
run for more than 5 continuous minutes less than an average of twice a
week. Otherwise, I use it periodically to clean out the bandsaw and
table saw accumulations.
Thanks for you help,
CDW
"Seawulf" wrote in message
news:dXpWd.84446$JZ2.14012@fed1read02...
I have a home workshop and needed 220 V circuits for certain power tools
and 120 V circuits for lighting and receptacles.
Around the same time our central air conditioning system faded and
died. We live in southern California and do not have many really hot
days, so we decided to not repair it again and just let it be.
The 220V 50A circuit for the AC happened to terminate on one wall of the
shop. So, taking advantage of the situation, I decided to set up a
subpanel using the former AC circuit. I am not an electrician, but have
done other electrical work around the house, including wiring attic
fans, adding new outdoor circuits, etc.
I added the subpanel and ran a 220/20A line (10-2G NM-B cable) to the
tablesaw and bandsaw and two 120/20 A lines (12-2G NM-B cable) for new
receptacles. The saws are each rated at 220V/13A and are never run
concurrently, One of the 120V receptacles was dedicated to a dust
collector rated at 120V/18A or 220V 9A.
I have been running this setup for about two years with no apparent
problems. I recently removed the cover on the subpanel to check
something and found that the neutral wire for the line feeding the dust
collector, and connected to the neutral bar was charred for about two
inches from the bus. Most of the insulation had been burned off along
those two inches. Also, the black plastic around the neutral bus shows
signs of having melted around the perimeter of the neutral bus bar.
The circuit breaker on the dust collector line was still engaged. I
also tested the cb and found that it does shut off power to the circuit.
I checked the screw which held the charred wire to the neutral bus bar
and it was tight I also checked the screw holding the neutral wire for
the other 120V line, and it was also tight.
The 50A line from the main box to the workshop subpanel is Aluminum
(house is mid 70's vintage) and the Murray subpanel in the shop is rated
for both Al and Cu wire.
Does anyone have any ideas as to what the problem could be?
Thanks,
CW
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