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Joined: Jul 2002
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I have not been here for a while. Hello to all.
I looked at a job, where the homeowner is replacing the range.
Existing is a 3 wire cable feeding an old range. Are we allowed to install a 3 wire cord and plug (using the old cable) for the new replacement range, or do we have to run a new 4 conductor cable back to the box?
Thanks - SJT
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Joined: Apr 2002
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SJT:
250.140 ('05 NEC) has all your answers. Read the exceptions, and note the word 'all' for the four (4) requirements to use an existing feeder.
Only '05 available right now. I don't remember if there were any changesfor this in '08
John
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Joined: Jul 2004
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Basically existing installations that were compliant in 93 are still OK. From 2011
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.
(1) 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.
(2) The grounded conductor is not smaller than 10 AWG
copper or 8 AWG aluminum.
(3) 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.
(4) Grounding contacts of receptacles furnished as part of
the equipment are bonded to the equipment.
Greg Fretwell
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Joined: Apr 2002
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Greg:
Thanks for the above. My laptop with most of everything.....is sitting in my office, and I'm not there.
John
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Thanks. It would be great if I could apply those exceptions, and use the existing cable.
It ends up that the new stove they bought is 13.9 KW.(convection oven)
When the ranges go over the 12KW, there is no demand factor for one that large?
I would have to wire this for the full 14000 watts, right?
Then 14000 divided by 240 equals 58 amps.
It will be a nice job, if they accept the estimate.
SJT
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Joined: Apr 2002
Posts: 7,411 Likes: 8
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Just a quick heads up.....check the capacity of the service!
John
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Joined: Jul 2004
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What kind of plug does that have?
Greg Fretwell
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Joined: Nov 2007
Posts: 764
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Thanks. It would be great if I could apply those exceptions, and use the existing cable.
It ends up that the new stove they bought is 13.9 KW.(convection oven)
When the ranges go over the 12KW, there is no demand factor for one that large?
I would have to wire this for the full 14000 watts, right?
Then 14000 divided by 240 equals 58 amps.
It will be a nice job, if they accept the estimate.
SJT Using Table 220.55, you would increase the demand value in Column C by 5% for each KW over 12KW, so in your case that would equate to 10% or an extra 800W which would be 8800W making it 36.6A at 240V. That puts you within the ampacity of #8 NM. Also, I agree that as long as you are not moving the location of the range, you can use the existing 3-wire setup with the new range.
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Joined: Jul 2002
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That's good that a larger range (13.9kw) is allowed to be derated like that. Thanks for all the input
SJT
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Joined: Nov 2007
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That's good that a larger range (13.9kw) is allowed to be derated like that. Thanks for all the input
SJT
Well, it’s definitely in there and you asked about it, but I often take issue with Art.220 and generally will only use the branch circuit ratings calculated there for sizing a feeder or service conductors, but I don’t know how many others share that opinion. I’ve always operated on the principal that since we are required to follow the manufactures listed instructions in Art.110, then those should take precedence over other Articles in the NEC. IMO, if the manufacturer specifies a particular size branch circuit or OCP etc., in their listed instructions, then I feel that is what should be used, not the ratings obtained in Art.220. Like I said though, that’s just my opinion.
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