Let's see if I can send to this list. . .
All this talk about dryer cords and grounding got me wondering. I dug out
the 1996 NEC, and an article
about the new 1996 NEC changes, and my 1996 NEC class notes, and the 1993
NEC Handbook. From
this I would guess that the reason your dryer has no separate ground wire is
that the NEC didn't require it at the time. As I see it, the dryer is OK
(grandfathered under the revised for
1996 section 250-60) and the air compressor would never be legal connected
the same way (section 250-
61(b)).
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>From Electrical Contractor magazine, 9/95
ARTICLE 250 - GROUNDING
Ranges, Dryers, and Ovens Now Require Four-Wire Receptacles and Cords
Section 250-60 Clarify intent of Code
The code no longer permits the grounded circuit conductor (neutral) to
ground the frame or junction box
of electric ranges, wall-mounted ovens, counter-mounted cooking units,
clothes dryers for "new
installations." Note: This change brings the NEC into alignment with the
Canadian Electrical Code,
which has always required four-wire supply cords for these appliances.
There is an illustration showing:
"Proper Installation" = a 4-prong receptacle with the 3-prongs straight up
and down, and a half round
ground pin (like a regular 3-prong 110V outlet, but with an additional slot).
VIOLATION = the three prong receptacle with the neutral connected to the
grounded conduit system at
the receptacle box.
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According to Gregory P. Bierals (my employer brings him in to explain the
changes to the code every
three years - he's the only man I've ever met that has actually memorized
the NEC. Ask him a question,
and he'll tell you the answer, the section the answer is from, and often the
page number it appears on in
the paperback edition.) "A significant modification has been made to Section
250-60 with regard to the
use of the grounded conductor (neutral) for the purpose of grounding the
frame. . . This provision will
only apply to existing installations and not to new branch-circuit
installations which will require an
equipment grounding conductor routed with the branch-circuit conductors as
the equipment grounding
means."
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Why did the code allow this in the past? This is from the 1993 NEC Handbook:
"The use of the grounded circuit conductor for grounding purposes is
contrary to other sections of the
Code. . . However, it has been allowed for many years because of the good
safety record of those
appliances that are grounded through the grounded circuit conductor and
because an open splice or break
in the grounded circuit conductor would normally render the appliance
inoperable. A subcommittee
reevaluated this requirement for the 1984 NEC and verified the continued
good safety record." It goes on
to explain exactly what would happen if this wiring practice should fail -
fire/injury/death.
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What does section 250-61(b) say?
"Load-Side Equipment. A grounded circuit conductor shall not be used for
grounding noncurrent-
carrying metal parts of equipment on the load side of the service
disconnecting means or on the load side
of a separately derived system disconnecting means or the overcurrent
devices for a separately derived
system no having a main disconnecting means." It lists 5 exceptions - none
apply to your air compressor.
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My $0.02:
** As always, check this with an actual residential electrician.** We don't
wire too many dryers or ovens
in our manufacturing facilities, so I'm no expert.
I've always understood existing installations to be grandfathered, until you
start to work on them. If you
make a change, you have to bring everything up to current code spec. So
right now, your dryer should be
legal. Connecting the air compressor this way would violate section
250-61(b). Spring for a new circuit
breaker and outlet. Parts and labor are cheap compared to people and
equipment.
If the compressor is portable, or at least able to move, I'd use a
twist-lock plug and receptacle as well. I'd
hate to be there if the plug gets pulled out or plugged in with the motor
on. Besides, it promotes domestic
harmony to not have the cars interfere with the laundry.
Ed
Ed & Laura Mulligan mulligan@fullnet.net
http://www.fullnet.net/user/mulligan
'92 5.0 LX "I love the sound of Flowmasters in the morning!"
MOUSE: "You're immune to both romance and mirth, you must be a. . . a. . ."
DILBERT: "That's right. I'm an engineer."
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