Re: 220v conversion question

On Tue, 1 Sep 2009 10:58:01 -0700 (PDT), "keithw86@xxxxxxxxx"
<keithw86@xxxxxxxxx> wrote:

This came up not too long ago and someone noted that between an early
manual and later the particular manufacturer of his dp had dropped the
illustration/wiring diagram for the split voltage, undoubtedly to
maintain strict Code compliance from a liability standpoint.  However,
they hadn't changed the wiring iiuc... :)

Their lawyers are dumber than stumps if they think paperwork is going
to get them out of the inevitable lawsuit. Do they have a compliance
(UL, etc.) mark on them?

I'm not sure if "dpb" was referring to me, or not, but I found that
with my DP. Motor can be rewired for 240, but the wiring harness has
no provisions for a neutral feed. The "stock" harness connects the
work lamp across the two non-ground leads so that if the DP is plugged
into a 120v circuit, the lamp socket sees 120. And if plugged into a
240v circuit, the socket sees 240v. I'd strongly suspect the OP's band
saw is similar. He'll certainly find out if he rewires the motor for
240 and his work light (with a 120v bulb) burns very brightly for a
very short time.

Several years ago, on the manufacturer's web site, the PDF manual for
the DP, as a part of the diagram for rewiring the tool for 240, showed
the work light socket being changed to connect across one hot lead and
the EGC to provide 120 to the lamp. I went back to the site at a later
date, and that part of the diagram was no longer there. It now shows
only a configuration that connects the lamp socket across the
non-ground leads with no direct connection to the EGC. I suspect the
diagram was deleted as a result of UL requirements.

Using the EGC for an operational conductor does violate the current
NEC. But, the NEC doesn't cover anything beyond the wall plug. It's
only applicable to permanent wiring, so rewiring the DP (or band saw)
to supply 120v from a 2+G 240 circuit doesn't technically violate the
NEC unless the device is hardwired into the facility wiring. That
doesn't mean it's any more or less safe, just that it's not covered by
the NEC. That's according to my understanding of the scope of the NEC.
Even if "plug in" loads was covered by the NEC, compliance would be
impossible to enforce unless you had to pull a permit and get an
inspector out every time you plugged the vacuum cleaner into the
living room wall socket.

Using the tool's EGC for a neutral return will, as stated, energize
the grounded portions of everything connected to that circuit, as well
as everything on every circuit which has an EGC connected to the
ground bus in the panel that houses that circuit. The voltage on those
energized grounds will be the product of the resistance to ground of
the panel's ground bus times the current flowing from the ground bus
to ground. May or may not be dangerous depending on the amperage and
the resistance to ground.

Incidentally that is the same condition that exists if any device
drawing current through that panel develops a short to ground. Until
the breaker trips (assuming the leakage to ground is enough to trip
the breaker) every grounded item in, or connected to, that panel will
be energized with that amps x resistance voltage.

The use of GFI breakers addresses that condition by tripping anytime
there is a very small difference in the amperage in the two non-EGC
conductors. Otherwise the fault current would have to be on the order
of the breaker rating. A DP or BS rewired to use the EGC as neutral on
a 240v circuit would certainly trip any 240v GFI breaker that
monitored the current in the two hot wires the way a 120v GFI breaker
monitors the current in the hot and neutral wires.

Tom Veatch
Wichita, KS
USA


.

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