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Joined: Apr 2002
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Even if you have all burners on for over 3 hrs it still would not be a continuous load. The elements in electric cooking appliance turn on an off even if they are on high. That is the reason for the demand factors in table 220.55. An appliance rated at 12kw (50 amps @ 240 volts) can be connected to a 40 amp circuit.
Curt
Curt Swartz
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Joined: Mar 2003
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Just to clarify I am talking about the branch circuit feeding the cooktop not the wiring within the cooktop.Just want to know what the min feeder wire size and OCP is for 7.7KW and whether the demand factor of 80% can be applied to use the already installed 10/2 romex and use 30A breaker.
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Joined: Apr 2002
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Gserve, A 30 amp branch circuit would be fine for this installation. I would make sure that the #10 wire installed by the factory is continuous and there wasn’t a good reason a 20 breaker was installed.
Curt Swartz
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Joined: Jun 2005
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334.80 NM cable ampacity refer to 310.15 at 60degree C. You start with romex derating at 30 amps. 422.10A allows the use of table220.19. That table allows derating of load serve. GREAT. But, fpn #4 to table. The branch circuit load shall be nameplate rating. If the ampacity at 100% is 32.8,then the 10 wire with no room for derating is not big enough. Unfortunatly you need to either disconnect a burner or rerun #8 nm on 35 cb. Also, Has anyone noticed that Trane brand AC condensors for homes are coming at maximum fuse 25,35,or 45. Whe make life more difficult?
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Joined: Mar 2003
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Where does my liability stop? I would not have known this had it not been hooked up to a 20A breaker by mistake. There is also a single built in oven where the load is only 3.3KW and 20a breaker would be enough and that 20A breaker was for that oven ,not the cooktop.Part of my job when running feeders to the manufactured home is to test things out and thats how I found out because cooktop was hooked up to 20A breaker by mistake and it tripped after a few minuets.
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Joined: Feb 2005
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I'm suprised that the cable is a two-conductor NM cable. The requirement for neutral-grounded (i.e., 3-pronged-plug) appliances has always (well, not always) been to use either service cable or an insulated-neutral cable, especially with mobile homes.
Larry Fine Fine Electric Co. fineelectricco.com
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Joined: Apr 2004
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As Curt noted above, try to determine that the wiring is 10-2 all they way to the panel, meaning there isn't some 12-2 spliced in there somewhere, if you can. Once you determine the run is 10-2 (or greater), you can install the 30 amp CB. Remember, the CB's job is to protect the wiring, not the appliance. A 30 amp CB will provide proper overcurrent protection for #10 wiring.
As to the Larry's post, we're all assuming the cable is 12-2G, meaning there is an uninsulated ground wire in there also.
Radar
There are 10 types of people. Those who know binary, and those who don't.
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I have varified that 10/2 romex was run from the panel to a crossover point (junction box)and then from that JB to a JB under the cabinet where the cooktop is.The 20A breaker was for the built in oven(3.3KW)They had them wired to the wrong breaker in the panel.ie:30A to oven and 20A to cooktop when the oven was supposed to be wired to the 20A and cooktop to 30A.
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Joined: Feb 2005
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I meant that the cooking appliances should have been fed with either a 12-3 or 10-3 plus-ground cable, or an SE cable, even before the separate-neutral-and-ground requirement.
Larry Fine Fine Electric Co. fineelectricco.com
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Joined: Jul 2004
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If they need a neutral they need a white insulated wire. It could also be the grounding conductor before 96 but it was still called a neutral and was supposed to be insulated. The exception allowed SE but I still saw inspectors say that had to be SER as long ago as 71. The normal installation I saw was the white went to the 3d prong of the plug and the ground landed on the backstrap of a bakelite receptrace or the box.
Greg Fretwell
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