On Tuesday, July 1, 2014 10:32:36 AM UTC-4, bob haller wrote:
Would you prefer it if it costs $1000 extra to run a new 4 wire cable
back to the panel? The comparison with the outlet isn't a good comparison,
because it's never been code to wire an outlet with the neutral
and ground shared. In the case of existing oven circuits, it's permitted
and common. From a technical perspective, a general purpose
outlet is typically different than a dedicated hardwired oven or oven
receptacle. In the case of outlets, there are typically multiple
outlets, lights etc on a circuit, more places for connections to come loose or
other problems to crop up. In the case of an oven, the shared neutral/grd
is on a dedictaed 8 gauge or better cicuit from the panel to the appliance.
Is 4 wire better and required for new circuit runs? Yes. Would I
go changing an otherwise adequate 3 wire circuit to 4, just to replace
an oven? No. Apparently all the oven manufacturers agree, because every
oven install manual I've seen shows how to connect it to either a 3 wire
or 4 wire circuit.
It probably should be pointed out that the change in the 96 code was
simply as an attempt by Phil Simmonds to create uniformity, not
because there was a pile of bodies to justify it.
The quote was "the war is over" in reference to copper shortages in
the 1940s that prompted the exception.
I have a 3 wire dryer circuit and I have no intention of changing it
any time soon.
BTW if your dryer is wired with Romex, legally, you probably have 4
wires in the cable anyway so fixing it is trivial. 10/3 without a
ground is pretty rare and the neutral is required to be insulated so
10/2-wg was not legal.
The one that was legal was 10/2 -wg SE cable as long as it was fed
from the main panel (where the service disconnect and main bonding
jumper resides). I never understood why that SE cable exception
existed but it was there.
I, for one...there's 75+ yr of existing practice that hasn't
demonstrated any real problem.
When had repair on the well a couple of summers ago, the well service
guys used section of 4-wire cable to replace the torn up section because
they said the current county Code req'd it as only they could run. Of
course, they then clipped the ground conductor on both ends since
there's nowhere for it to go, anyways. About as stupid as blindly
replacing a 3-wire for a 4-wire in a range/electric dryer app.
On Tuesday, July 1, 2014 2:44:02 PM UTC-4, Scott Lurndal wrote:
Not always, but I'd say appliance installation instructions from
dozens of manufacturers of ovens, ranges, dryers is. And they all say that
you can hook it up to an existing 3 wire or 4 wire circuit. Also there is
OMG, someone is gonna die!
I guess we should all just pack up and close down AHR, because you
don't know the answer. The same could be said of most of the questions
on AHR. Good grief.
What about "anonymous" posters who happen to have read/know what the NEC
"250.140 Frames of Ranges and Clothes Dryers
Frames of electric ranges, wall-mounted ovens, counter-mounted cooking
units, clothes dryers, and outlet or junction boxes that are part of the
circuit for these appliances shall be connected to the equipment
grounding conductor in the manner specified by 250.134 or 250.138.
Exception: For existing branch-circuit installations only where an
equipment grounding conductor is not present in the outlet or junction
box, the frames of electric ranges, wall-mounted ovens, counter-mounted
cooking units, clothes dryers, and outlet or junction boxes that are
part of the circuit for these appliances shall be permitted to be
connected to the grounded circuit conductor if all the following
conditions are met.
The supply circuit is 120/240-volt, single-phase, 3-wire; or
208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.
The grounded conductor is not smaller than 10 AWG copper or 8 AWG
The grounded conductor is insulated, or the grounded conductor is
uninsulated and part of a Type SE service-entrance cable and the branch
circuit originates at the service equipment.
Grounding contacts of receptacles furnished as part of the
equipment are bonded to the equipment."
On 7/1/2014 10:37 AM, email@example.com wrote:
Excepting that Cu is so pricey now that folks are ripping up installed
AC units and stripping ground wires from power poles and the like...so
let's just willy-nilly drive needless usage/demand/price even higher.
Makes sense to me... :(
Certainly wasn't rare at all back when many of these installations were
Because SE cable covering is rated for the voltage insulation whereas NM
outer jacket may not be; it's an outer sheath to hold the conductors
together physically with some insulating property but not qualified as
insulated per UL listing/Code.
Besides the aforementioned Code exception that doesn't require and
expressly permits the continued usage of 3-wire in existing
applications, there are a number of alternatives for rework/existing
work allowed by Code to add the ground if that is really, really, really
wanted besides running a new 4-wire cable the full distance.
These include pulling a separate ground and also exceptions that that
added ground doesn't necessarily have to follow the same path or even be
grounded at the same terminus. For the specifics see the Code or
consult local Code gurus.
ADDENDUM to this story...
I've not researched this point in detail but I think this is a place
where the requirement quoted above is, in fact, a case of
misinterpretation of the NEC requirements as there is for the well pump
nothing but a single 240V load; there is no neutral current return from
a 120V circuit as is the situation trying to be avoided by the update to
the Code as there is in the case of the range or dryer.
Turns out we may be forced to drill a new well before long; I'm certain
to research this in depth (so to speak :) ) before spending an extra
third for 4-wire down a 300-ft hole when there's nothing for that fourth
conductor to do anyway except take up space and add to the expense.
If I'd been on the NFPA Code Committee when this came up I'd have voted
"no" simply on the cost/material basis of there being no demonstrable
real problem being solved that justified the added expense. "Parsimony"
is a virtue in engineering, too...
On Wednesday, July 2, 2014 6:06:27 PM UTC-4, dpb wrote:
I would agree that the well situation is a
misinterpretation of the code by someone. Even in cases where you
think the code section is excessive on some point, I've always
been able to see some point to doing it. To insert a section of 4 wire
cable in the middle of a 3 wire and leave the 4th unconnected,
obviously does nothing. Also, 240V loads are routinely connected
and are code compliant without a neutral all the time. That's how
wells are done here. So, I'd say either this is the well guys that
don't know what they are talking about, or else some local inspector
type that issued some edict either incorrectly or incorrectly interpreted,
Do you have any reason to believe it's part of the NEC?
A, as you say, it makes no sense at all from any physics
B, wells here are put in with 240V, 2 hots + ground all the time
and they pass electrical inspection.
I was mixing both topics here and switched back once too quickly,
No, I do _NOT_ think there's likely anything in NEC that justified the
4-wire cable in the well-hole; I have yet to discover from whence came
the supposed edict referred to by the well service guys...
What I was speaking of in the "voting against" comment is the new
section that requires the 4-wire for the grounding of the oven/dryer
branch circuit. There as you I do see there is at least an issue; I
just don't agree that the disease is worth the cost of the cure given
the history (or more correctly, the lack thereof) indicating it is a
safety issue of any magnitude at all.
I obviously wasn't in the room but I'd have had to seen an impressive
litany of cases where it had been the root cause of a problem and if
that were to have been demonstrated then I don't see how it could have
been justified to leave the exception standing. Making the change was,
imo, just bureaucracy doing what it does in this case. Most of the time
NFPA does a pretty good job but I think they misstepped on this one.
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