Household Range Wiring

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czars

Czars
Location
West Melbourne, FL
Occupation
Florida Certified Electrical Contractor
I have had several instances lately where clients have called with complaints about their household ranges not operating. In all cases I found that the homeowners had replaced their older ranges with a newer and fancier ranges. In all cases the original ranges were 8kW to 9.6kW (33A to 40A) and were supplied from 40A breakers via #8 conductor cables. Also, in all cases, the newer ranges were 12kW to 13.8 kW (50A to 57.5A). In most cases, the 40A breakers just kept tripping however, in one case, the 40A breaker melted.

Rewiring for the newer ranges has presented me with some dilemmas that I would like some assistance in resolving. I know that 2002 NEC 422.10A, last paragraph, states that branch circuits shall be permitted to be in accordance with Table 220.19 (Demand loads). However, 422.10A, first paragraph, states that the branch circuit rating shall not be less the marked rating of the appliance.

Take the case of the 13kw range (54.2A). Clearly from the 2002 NEC Table 310.16, a supply cable with #6 conductors is required and may be protected by a 60A breaker (NEC 240.4B). If the range is to be plug connected and the range cable, plug and receptacle are rated at 50A are these parts acceptable for use?

What should be circuit configuration for a 13.8kW range (57.5A) consist of? Should it be hard wired with #4 conductor cable and a 60A breaker? That would certainly provide the necessary current carrying capacity.

I welcome any assistance.
 
Re: Household Range Wiring

czars said:
Also, in all cases, the newer ranges were 12kW to 13.8 kW (50A to 57.5A). In most cases, the 40A breakers just kept tripping however, in one case, the 40A breaker melted.
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The rest of the questions aside, a 40-amp breaker should be able to handle, and interrupt, current in this range without damage. Have you tried a clamp-on ammeter to see if the breaker is performing as it should be? This sounds like equipment failure.
 
I agree with Larry Fine, the 40A breaker that melted should have been able to handle the overload and it does sound like equipment failure. Nevertheless, the other questions remain about the size of service and equipment ratings.
 
Those people must be doing some heavy duty cooking. :? This topic was just visited as others have said and the opinions were fast and furious. In my experiences with new construction around here, we use #8 NM-B with a 40A breaker for ranges. 210.19 (A) (3) I have never had a call back or problem with this scenario. I'm sure others will chime in.
 
The NEC gives us "demand factors" as a way to recognize that not all connected equipment is likely to be running at the same time. That notwithstanding, there is nothing to prevent a homeowner from turning on everything in the home, even running both the heating and the A/C, all at the same time. When that happens, the demand factors become meaningless, and it is likely that something will trip.

So it should not surprise anyone if a 40 amp breaker that feeds a 13.8 kw range might trip, especially if the homeowner is showing off the new toy by turning all burners to "high" and turning the oven on to "clean." If that causes a breaker to melt, and not trip, I would suspect the breaker, and not the range, as being the failed component.
 
jeff43222 said:
. . . sit a spell.
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If you're going to try to speak "Southern," then you need to get the spelling to match the pronunciation. It's "set a spell." :wink:

(p.s. Disregard what it says in my signature below - I'm a native Texan.)
 
m73214 said:
Those people must be doing some heavy duty cooking. :? This topic was just visited as others have said and the opinions were fast and furious. In my experiences with new construction around here, we use #8 NM-B with a 40A breaker for ranges. 210.19 (A) (3) I have never had a call back or problem with this scenario. I'm sure others will chime in.
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This was a lenghty thread recently,For basically the same ytpe of high KW appliance.#8 nm and a 40 ocpd has been the residential norm for years but with the advent of NEW TECHNOLOGY it seems that maybe the norm has its pitfalls.Whem a home is bid it gets a bid for a 40 amp range circuit.I would put it on the GC if they sell an upgrade that has a higher ampacity than the NORM.We bid a 40 they sell a 60 who`s responsible to upgrade the electrical portion.The EC I think not since when bid they bid a 40 and the bid was accepted.
Last year I did a service call for bath lights dimming.The HO had told the sales people that they wanted to be able to iron thier clothes in the closet that was accesed through the bathroom. and wanted a receptacle.The extra was written up as a receptacle in the closet with location marked connected to existing circuit.The home owners complaint was when they used the iron the bath lights dimmed.My answer was yes they do dim but there is nothing I can do since it is off an existing circuit :wink: I could feel for him but could not help him.He asked what could be done and I told him there are two choices add a dedicated circuit he would have to pay for or turn off the bathroom lights so they didn`t dim :roll:
 
allenwayne said:
. . . .or turn off the bathroom lights so they didn`t dim
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:lol: :lol: :lol:

OK. Let's have a moment of silence in recognition of the difficulties this homeowner is facing.
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That's enough.

. . . .or turn off the bathroom lights so they didn`t dim
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:lol: :lol: :lol:
 
charlie b said:
. . . there is nothing to prevent a homeowner from turning on everything in the home, even running both the heating and the A/C, all at the same time.
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Really? Unless they're isolated systems, this would be a fancy trick.
 
LarryFine said:
charlie b said:
. . . there is nothing to prevent a homeowner from turning on everything in the home, even running both the heating and the A/C, all at the same time.
Click to expand...

Really? Unless they're isolated systems, this would be a fancy trick.
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Nah, all it takes is a couple of jumpers. I have seen it done; once. A guy just wanted to prove a point and win a bet. :twisted:
 
dlhoule said:
LarryFine said:
charlie b said:
. . . there is nothing to prevent a homeowner from turning on everything in the home, even running both the heating and the A/C, all at the same time.
Click to expand...

Really? Unless they're isolated systems, this would be a fancy trick.
Click to expand...

Nah, all it takes is a couple of jumpers. I have seen it done; once. A guy just wanted to prove a point and win a bet. :twisted:
Click to expand...

Ah, the "you-can't-protect-people-from-themselves" syndrome. :roll:
 
Yes, if you read the code, ranges have lower than nameplate allowances due to demand, and like it was said, all of the various heating elements will not normaly be on at the same time. This is why ranges have demand factors, but a stand alone cooktop or wall mounted oven are not multi-purpose and multi-element units, so the rating of these is nameplate with no demand factor. I just did the branch for a 13.2 KW unit and put it on a 40A because the 8KW was only increased by 1.2 x 5% (13.2KW-12KW=1.2, *5%)=480. So 8000W + 480W= 8480W/240=35.33 Amps.
 
I don think we have anwsered the OP question.

If we do want to feed the range with a 60A circuit, even if its not required, how can this be done?
 
First you would have to check the manufacturer's installation guidelines for the supply circuit. Many times with equipment not only is the minimum branch circuit given, but also max OCP, to protect the unit itself from self distruction. Oversizing could void warrantees, and installing a new or using a previously installed dedicated supply circuit for a unit means providing what it is listed and labeled for in the instructions per NEC. Simply overbuilding in equipment supply circuits may not be an option. It is a strong possability that the equipment will say Max OCP at 50 A in the installation instructions, so the intent by the instructions is to protect the unit, not just the supply wire.
 
It looks like I am not the only one with questions about how to "properly" wire the ranges for safety. Unfortunately, there don't seem to be many answers.

Demand factors are great, but only if you are talking about a large number of ranges such as you would find in an apartment building. However, when granny is cooking Thanksgiving dinner for all of her family, all four burners will likely be on while the turkey is in the oven. Granted, the oven and the burners may be cycling, but there is no mechanism present to prevent all from being on at the same time. I've seen enough problems to make me a believer in matching the circuitry to the range. I wire the range with equipment rated to handle the range nameplate load. If the range rating is above 50A I hard wire the range with conductors and breakers that can handle the load.

I think that this is one area where the NEC needs some revision to insure safety. Allowing 8kW wiring for a 12kW range doesn't make any more sense than allowing the same wiring for a motor just because the load on the motor will likely be low.
 
Well seeing as how it is sunday, anybody out there making a big sunday meal tonight? Here's a suggestion:
Put a monitoring clamp-on ameter on one of the range legs. Tell us what the rating of the range is, and tell is the average draw, and the highest spike you get. Lets see what the readings are and take all the guess work and conjecture out of it. If a few people do this today we can get a good idea of what the actual conditions are out there "home on the range". I also agree that if there was a failure of a breaker and buss connection, the CB was not the weakest point in the circuit, as it should have been to protect it.
 
Sorry, we can't be part of this test. We replaced our electric range with a gas unit last year. It's actually a kind of interesting story. We got a call from a woman who was deathly afraid of her "gasoline" stove and the tank outside, and wanted a price for a circuit.

While there, and after giving up on explaining the difference between gasoline and LPG, we asked about the replacement and the fate of the "gasoline" range. (Patricia and I have always wanted a gas unit, but our electric still worked, so we still used it.)

The customer said that now she had to go shopping, and then I came up with a brilliant plan: let's swap ranges! Both were in perfect working order. She loved the idea, too. Not only did her father transport both units, we still got paid for her new circuit.

The only work we had to do at home was run a new gas line, which was easy because we had run a new line outside to a pedestal-mounted grill a few months earlier; we just teed in. We also had to adjust the orifices, since we don't have "gasoline" here.
 
Larry B. Fine

We also had to adjust the orifices, since we don't have "gasoline" here.
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I am curious Larry. What do you use in your vehicles? I am looking into possibility of buying a new vehicle less dependent on gasoline.
 
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