0

My old range is on a 60 amp circuit. I'm replacing the range with an oven (40 amp) and cooktop (30 amp).

I currently have a Siemens 60 amp breaker and label states awg 6-4. I want to replace it with a 70 amp breaker where label also states awg 6-4. So is it ok to change the breaker from 60 to 70 without changing the old wire?

Don't know size of wire. But I assume is 6. So if it is 6, do I need to change the wire?

Update: Thank you for everybody's reply. I don't know if this info helps. The cooktop is 8300 watts and the oven is 6325 watts. I currently have a 60 amp breaker. Can I just use the 60 amp breaker and not even changing it to 70 amp? Cause that would be the best option for me.

Improve this question
4
  • It's entirely likely that your new oven and cooktop will work comfortably on a 60A circuit. You would need to use both devices near max to trip the breaker. Anyone see an issue with that? – Stanwood May 15 '18 at 15:58
  • What type of cable is in your wall for this circuit? – ThreePhaseEel May 15 '18 at 23:37
  • Also, what make and model are the new oven and cooktop, or can you provide their installation instructions for that matter? – ThreePhaseEel May 15 '18 at 23:38
  • It's Bosch appliances. The cooktop is NET8068SUC and the oven is HBL5451UC. If I don't have to change the 60A breaker, then that would be best. I assumed that cooktop (40A) + oven (30A) = 70A breaker. – Wes May 16 '18 at 12:15
2

This isn't just an adding job

Your assumption that your oven & cooktop combination requires a 70A breaker is actually incorrect -- this is due to the 220.55 demand factors in the NEC, as it's pretty implausible that the oven will be going at full broil and all four cooktop elements will be on full blast all day long on other than very rare occasions. (That, and neither of your appliances require a dedicated branch circuit in their installation instructions.)

Applying the logic of table 220.55, note 4:

  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.

to our circuit gets us a total unfactored load of 14.625kW. Since this is over 12kW, we must then apply 220.55 note 1 to the 8kW column C value for a single range to get the factored load:

  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.

Applying this logic gives us a 15% increase in demand, or 8*1.15 = 9.2kW, which is well within the capacity of a 60A branch circuit! (In fact, you could run this combo off of a 50A branch circuit if you so chose.) Given that the use of 220.55 factoring for range circuit sizing is expressly permitted by the NEC in 422.10(A), paragraph 4:

Branch circuits and branch-circuit conductors for household ranges and cooking appliances shall be permitted to be in accordance with Table 220.55 and shall be sized in accordance with 210.19(A)(3).

we can safely say that you don't need to change your breakers here, as the factored load is considered the "maximum load served" for the purposes of 210.19(A)(3).

Improve this answer
0

70A on AWG 6 will rise to 70°C safely but you lose some heat in the wire

It depends on your existing wire. Certain thermoplastic wet/dry wire is suggested for 55A operation. If this is yours then 70°C is excessive and not rated for 75°C

Not good is UF or TW

Type UF is covered by heavy plastic sheathing. The cable is designed for placement in the ground without being encased in protective metal conduit.

Type TW wire has a thin thermoplastic insulation that provides the wire with some measure of moisture resistance. However, for maximum protection, the wire has to be encased in conduit

Improve this answer
9
  • 1
    Where do you obtain terminations fit for that temperature, and isn't there a rule that forces you into the 60C column regardless? – Harper - Reinstate Monica May 15 '18 at 15:53
  • See NEC 110.14.C. For the 60 deg collum restrictions. +. 70 amp on #6 wire would be a code violation per the NEC. This has been the rule for as long as I can remember, – Ed Beal May 15 '18 at 16:09
  • Receptacles are often rated for 75’C with 30’C contact rise after 50 insertion cycles at full load – Tony Stewart Sunnyskyguy EE75 May 15 '18 at 16:10
  • Ovens and stove tops are rarely all on for 15minutes continuous for the wire to heat up. They cycle on and off. But if you can, you should reduce the load or keep the breaker at 60A and add more wire if it trips . – Tony Stewart Sunnyskyguy EE75 May 15 '18 at 16:26
  • Siemens 2-pole QP breakers have terminals rated to 75C. That only gets you to 65A with 6 AWG Cu (column B). – Stanwood May 15 '18 at 16:28
0

Short answer: Maybe

As Ed Beal points out, #6 is good for 55 amps so you can go to the next higher standard size breaker or 60 amps. However, if your breaker and equipment are marked for 75°C then #6 is good for 65 amps and you can go to the next higher standard size breaker or 70 amps.

So is it ok to change the breaker from 60 to 70 without changing the old wire?

Is your equipment and breaker marked for 75°C?

The GE ovens I am looking at call for a 20 amp circuit and the induction cooktop is 50 amp circuit. I think your amperages for your appliances is reversed. The cooktop normally draws more than the oven.

Good luck!

Improve this answer
0

I agree with @Harper #6 copper is limited to 55 amps per code table 310.15.B.16 60 degree column per 110.14.C less than 100 amp the 60 degree column is used. With that said if we know the actual manufacturer's rated value for each of the units it may be possible to use existing wiring as derating is allowed per table 220.55 of the NEC. And use the tap rule to power both but the actual wire size will be needed and the rated value of the oven and stove top. Added without knowing the rated values just the amperages given I doubt you would trip the breaker even with all burners on and the oven on, the reason I state this is because the breakers used are inverse time breakers a 60 amp breaker will allow 3 to 5 times its value for around 30 seconds as the value is reduced it will hold longer at about 65 amps (from memory) a 60 amp will hold for close to 20 minutes, most ovens heat to the desired temp in this time and start cycling, similar affects to the stove top coils happens so even with everything turned on the max current is rarely used and the derating factors are allowed.

Improve this answer
1
0

First, consult the installation instructions for each of the appliances. Those instructions are law. Literally, your state legislature has incorporated NEC into state law, and NEC 110.3 absolutely requires following installation instructions. Because, UL/CSA only tested it in those conditions, so the UL listing depends on proper installation.

It is not uncommon to have one single circuit supplying both range and oven. Code allows this and so do many appliance manufacturers.

Regardless, a #6 cable is only good for 55A@60°C, 65A@75C, and 75A@90C, (NEC table 310.15(B)(16). Generally you are required to use the 60C column for residential branch circuits (you can bump from 55A to 60A because you're allowed to round up to the nearest offered breaker size). If you want to go higher, you'd need to find a specific exception in Code, and then argue that with your local authority having jurisdiction (city inspector), and then he decides. I'm at the limits of my ability to advise; I wouldn't expect to get away with 70A on #6.

If the appliance instructions require (or if you prefer) a separate circuit and cable for each appliance, then I would retain the #6 (it's overkill for a 40A circuit but is a nice fallback if you ever install a 50A or 60A range/oven) and add a #8 or #10 to handle the other circuit. You are allowed to use oversized wires. If the #6 is a 3-wire ungrounded circuit, then I would definitely lay a parallel 10/3 or 8/3 - and use its ground to properly ground the obsolete #6, so it is now a 4-wire grounded circuit. This is allowed in ground retrofit rules: grounds can be shared, so you now have two 4-wire circuits on 7 wires.

Improve this answer
0

I=(8300+6325W)/Vac = 14625W. /240V =60.9A

Given that stove top elements and oven cycle with some duty cycle .

I stated before a 60A breaker will be safe but marginal as load rating but ideally should be 80% of breaker so optimal solution is AWG 4 and a 70A breaker , but AWG 6 will work at a slightly higher temp of a 60 deg rise worse case with 60A breaker has a low probability of being reached with normal usage.

Improve this answer
0

You should leave the 60A breaker, worst case is a breaker trip if all is on at full power, in that case, just reset the breaker and slow down a burner.

Also remember breakers are there to protect WIRES not appliances.

Improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.