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.
John Grabowski wrote:
You didn't move the 50A breaker in the main panel, did you?
If you've somehow got both the hots feeding the subpanel
on the same phase, that would overload the neutral, too, and some
panels allow you to do that. (It would also explain
why the AC unit croaked.)
Interestingly, when I tested the connections on the subpanel, although
all of the screws on the Neutral bus were tight, the screws on the two
hot phase wires were not tight. I got at least 1/4 turn on each. They,
along with all others have been re-tightened. But, it looks like I
really need to follow Charley's advice relative the the Al wiring being
cleaned and anti-ox paste used, etc. as well as replacing the subpanel
The amp meter would be used to measure actual amperage on the active
circuits to check for over-amp conditions?
BTW, I did verify the language on the Murray subpanel relative to being
rated for AL and Cu wire. The UL Panelboard Marking Guide stipulates
the phrase "Use Copper or Aluminum Wire" for this situation. The panel
actually reads "Use Cu/AL wire on pannelboard line and neutral
terminals." These two statements seem to be the same to me.
Thanks for your comments,
Run a new copper wire to the outlets. 18 amps is quite a draw, and the
risk of a fire ain't worth going cheap. What would the insurance
adjuster think of your setup? 240 V to the dust collector is actually
safer in this case, i think.
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