Doug Miller wrote:
In article dXpWd.84446$JZ2.14012@fed1read02, Seawulf wrote:
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.
You may find that to be a problem when you try to sell the house. Separate
issue, I know, but something you should keep in mind.
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.
Does that circuit have both a neutral and a ground? If not, it's *not*
suitable for feeding a subpanel, and must be replaced.
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.
That dust collector circuit is a potential problem. Depending on how long you
use it at a time, it may meet the Code definition of a continuous load and
thus require that the ampacity of the circuit be derated 20% to 16A. This
should have been wired with 10ga wire, which can carry up to 24A of continuous
load current.
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.
Wow.
No damage to the neutral conductors for the other circuits, right? Then
there's something amiss with that circuit, or with what's plugged into it.
I think you oughta have a look at that dust collector motor. You said (above)
that it's a dual-voltage motor. I wonder if the jumpers are set for 240V
instead of 120V.
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.
That doesn't mean that it will trip at the proper current draw, though.
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.
I hope the wire in that cable is at least 6ga minimum if the conductor
temperature rating is 75 deg C or higher, or 4ga minimum for 60 C conductors.
Does anyone have any ideas as to what the problem could be?
Check the jumpers on the dust collector motor and make sure they're set for
120V operation.
It is labled as 120 and I checked the actual wiring agains the 120V and
220V diagrams for the unit and it is definitely wired for 120V.
Also check to make sure there's adequate air flow for the dust collector. If
it's having to work too hard to draw air through too-small piping, it will
draw more current too.
Redo that circuit with 10ga wire. And replace the receptacle: it's probably
damaged too.
Check the connections on the cable that feeds that subpanel, at *both* ends
of all four conductors. (You *do* have four, don't you, two hots, neutral, and
ground?) If the neutral isn't tied down tight at both ends, you may be getting
a higher voltage in one leg of the subpanel than the other. Won't make any
difference to your 240V tools, but it plays hell with 120V devices. You might
have been pumping 150V or so through the dust collector.
Tje Neutral was tight at both the Main and Subpanel.
If the circuit feeding your subpanel has only three conductors, replace it
with the proper cable. Might as well switch to copper while you're at it. For
50A, you need 8/3 with ground (conductor temp rating 75 deg C or higher), or
6/3 with ground (conductor temp rating 60 deg C).
Yes, the 5A 220 feed from the main panel has two black, a white and a
ground wire. It is difficult to read the label on the sheathing - red
text on grey sheath. It is either 6 or 8 gauge and I can't really make
out much more of the ratings on the part of the cable that is exposed.
--
Regards,
Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
Thanks for your comments,
CDW
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