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What amp breaker should I use for a 20 Amp electrical oven and a 40 Amp range?

Currently, I have a 6 gauge wire and a 50 Amp breaker, and my current electrical cooktop and electrical oven are both hooked up to this.

I want to replace my current cooktop and oven with a 40 amp electric cooktop (induction-type) and a 20 amp electric oven.

Do I need to update my 50 Amp breaker to be a 60 Amp breaker because the total of the two new appliances is 60 amps? Would the resulting system (6 gauge wire and 60 Amp fuse) be safe for the combined cooktop and oven and within California code?

If helpful, the model and electrical specifications for the two appliances are listed below.

Frigidaire Professional 30'' Induction Cooktop

  • Amps @ 240 Volts: 35.0 / 35.1
  • Connected Load (kW Rating) @ 240V: 8.4 / 7.3
  • Minimum Circuit Required (Amps): 40A
  • Power Supply Connection Location: Right Rear
  • Voltage Rating: 240V / 208V, 60Hz

Frigidaire Professional 30'' Single Electric Wall Oven

  • Amps @ 240 Volts: 20.8 / 18.3
  • Connected Load (kW Rating) @ 240V: 5.0 / 3.8
  • Minimum Circuit Required (Amps): 20A
  • Power Supply Connection Location: Left Rear Bottom
  • Voltage Rating: 240V / 208V, 60Hz
  • 2
    This answer might be helpful. – Tester101 Aug 23 '14 at 0:50
  • I would think the % should be 100% in case using all components at the same time. bringing it to a 60 amp – user60838 Oct 3 '16 at 0:52
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Column C

First off you'll notice the text "Column C to be used in all cases except as otherwise permitted in Note 3.)", in the title of table 220.55. This makes it simple. You have 2 appliances, so follow that over in the table, and you'll see 11 in Column C. So there you go, you can just use 11 kW. Done.

11,000 W / 240 V = 45.8333 A

So you'll need a 50 ampere breaker, and wire sized appropriately for the load.

Note 3

Note 3 says:

  1. Over 1 3⁄4 kW through 8 3⁄4 kW. In lieu of the method provided in Column C, it shall be permissible to add the nameplate ratings of all household cooking appliances rated more than 1 3⁄4 kW but not more than 8 3⁄4 kW and multiply the sum by the demand factors specified in Column A or Column B for the given number of appliances. Where the rating of cooking appliances falls under both Column A and Column B, the demand factors for each column shall be applied to the appliances for that column, and the results added together.

Perfect, so instead of just using the value from column C you can do math. Let's step through it.

...it shall be permissible to add the nameplate ratings of all household cooking appliances rated more than 1 3⁄4 kW but not more than 8 3⁄4 kW...

8.4 kW + 5.0 kW = 13.4 kW

...and multiply the sum by the demand factors specified in Column A or Column B for the given number of appliances...

Let's check the table again... You have 2 appliances, both between 3 1/2 and 8 3/4 kW. So You'll look at column B, and find 65%.

13.4 kW * 65% = 8.71 kW

8710 W / 240 V = 36.2916 A

So using this method you can use a 40 ampere breaker, and appropriately sized wire. However, keep in mind that if you change the equipment, you'll have to do the calculation again. So while you can use this value, you may have to upgrade the circuit later if you change equipment.

Note 4

I'm not exactly sure how note 4 comes into play, but I think it can be used if this is the only equipment on the branch circuit. Just for fun, let's run through that one too.

  1. Branch-Circuit Load. It shall be permissible to calculate the branch-circuit load for one range in accordance with Table 220.55. The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance. The branch-circuit load for a counter-mounted cooking unit and not more than two wall-mounted ovens, all supplied from a single branch circuit and located in the same room, shall be calculated by adding the nameplate rating of the individual appliances and treating this total as equivalent to one range.

You're only concerned with the second half of this note, since you have one counter-mounted cooking unit, and one wall-mounted oven, all supplied by a single branch-circuit, and located in the same room. So you can add the nameplate values, and treat it as a single range.

8.4 kW + 5.0 kW = 13.4 kW

So you can treat the units as a single 13.4 kW range. Check the column C again, this time for a single range. You'll find a value of 8 kW. But wait... The column header says "(Not over 12 kW Rating)". Your range is 13.4 kW. That's bigger than 12 kW. Now you'll have to check note 1

  1. Over 12 kW through 27 kW ranges all of same rating. For ranges individually rated more than 12 kW but not more than 27 kW, the maximum demand in Column C shall be increased 5 percent for each additional kilowatt of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kW.

That's easy enough.

13.4 kW - 8 kW = 5.4 kW

Since .4 is not a "major fraction", you can just use 5 kW. So you'll have to add 5% 5 times.

5% * 5 = 0.25
8000 W * 0.25 = 2000 W
8000 W + 2000 W = 10,000 W

That means you'll have to use 10 kW as your demand.

10,000 W / 240 V = 41.666 A

Which means you can use a 50 ampere breaker, and appropriately size wire.

  • I suspect you must use note 4 when the conditions it gives are met... – ThreePhaseEel Jan 28 '15 at 2:01
4

You'll need to do more work than that - you'll need not only a 60-amp breaker but also #4 NM-B (#6 is too small to be legal on a 60-amp breaker) from the panel to the range/oven.

Provided that you never run the oven and the entire cooktop at maximum capacity at the same time, you probably will never trip that existing 50A breaker. If there's ever a moment, though, when you can't guarantee that everything's not running at the same time, you'll get into trouble. Best do the work now - you'll have to do it sooner or later.

  • Thank you so much for your reply. By "get into trouble", is there a fire/safety danger, or just that the 50A breaker would trip and shut-off the range and oven? – Dave Aug 22 '14 at 21:40
  • Ideally, the breaker would just trip. Depending upon the length of the wire run between the breaker and the oven, though... it might possibly not. I've seen 20A breakers notably NOT trip on a dead short circuit on #12 wire just because it was a long run. If it does not trip, then the house wiring will get hot from the too-heavy loading. If it gets hot enough, it could possibly start a house fire. I know, that's a lot of "if"s. I'd love to hear you report back that your range/oven circuit has just been rewired with #4, with a matching 60A breaker. I'd sleep much better. – TDHofstetter Aug 22 '14 at 21:53
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    If the breaker doesn't trip before the wire overheats then breaker should be replaced. Breakers have at least two ways of tripping, one is an electromagnet that should trigger if there is a massive overload, and the other is a bi-metal arm that will trip if there is a large load on it for some time. The reason for the bi-metal arm is so that short duration overloads don't trip the breaker. If it didn't, your vacuum could overload a 15A breaker when you first start it; all by itself. So if you have a short on a long run, it will take a while for it to trip the breaker, but it will eventually. – Brad Gilbert Aug 23 '14 at 22:05
  • See @Tester101's answer below -- it turns out that I was applying note 4 incorrectly when I upvoted this answer. (You still apply the demand factors to the single range load generated by the note 4 procedure.) – ThreePhaseEel Jan 27 '15 at 23:24
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Cooktop 8.4 kw Oven 5.0 kw Table 220.55 column B note 3

8.4 kw× .65=5.46 kw

5.0 kw× .65=3.25 kw

5.46 kw+3.25 kw=8.71 kw 210.19 (A)(3) For ranges 8.75 kw and over the minimum branch circuit is 40 amp. Your 50 amp circuit should be fine.

  • 1
    Could you quote the notes for Table 220.55 so we can see how you arrived at permission to use Column B? – TDHofstetter Aug 23 '14 at 4:25
  • Note 3 "over 1 and3/4 kw through 8 and3/4 kw in lieu of the method provided in column C, it shall be permissible to add the nameplate ratings of all household cooking appliances rated more than 1 3/4KW but not more than 8 3/4KW and multiply the sum by the demand factors found in column A or column B for the given number of appliances. – user24125 Aug 23 '14 at 5:43
  • I get 44.72A from 220.55... but I'd still be pretty tense about using that table to determine whether it's permissible to use a 50A circuit because it's clear that the cooktop/oven can easily use in excess of 50A at any given time. It's not always a good idea to do something that's legal if it's also unsafe. Heck, suicide is legal in some states. – TDHofstetter Aug 23 '14 at 11:55
  • Can you show me the calculation and reference for that number. If you don't trust the NEC you can go over and above what it says. After all it is a minimum standard. – user24125 Aug 23 '14 at 13:37
  • No reference, the calculation is simple & straightfoward - it's the sum of 80% total cooktop current and 80% total oven current, both are nameplate ratings. The 80% is drawn directly from ... oh, I see. You used the figure for two appliances, and the current you came up with that way (36.335A) is very slightly more than the cooktop's rated current draw. That assumes that if the cooktop is fully in use, the oven will never be running, or that the cooktop will automatically detect the oven's draw and shut itself halfway down. Is either a valid assumption? – TDHofstetter Aug 23 '14 at 14:09

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