Electric Subpanel fire

[Seawulf]

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:

[Goedjn]

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.)

[Seawulf]

No. Nothing was disturbed on the main panel.

My 220V table saw and band saw have both been operating off the panel for a few years, now. So, that indicated to me the phasing on the panel is correct.

Thanks for your comments, CDW

>

[Seawulf]

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 enclosure.

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, CDW

bumtracks wrote:

[bumtracks]

you need to tighten all the alum connections , both ends the feed at main panel and sub panel connections and would be wise to invest in a simple clamp on amp meter..

[Porky]

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. JohnK