I would er on the side of safety and use a 40 amp breaker.
After all your not going to have everything running at full tilt at the same time.
And if it calls for a min 40 amp appliance cord, it's saying 40 amps will do it just fine.
Going with heavier wire is ok though.

 

Based on the NEC all you need is a 40 amp circuit. #8 copper nm cable

 

You need a 4 wire range cord which usually is bought when you buy the unit. Unless your range outlet is 3 wire then you can get by with a 3 wire range cord.

 

Even though the calculation may come out to be 35 amps then NEC requires that any range 8 3/4 and over is to be on a 40 amp circuit

210.19(A) (3)

(3) Household Ranges and Cooking Appliances. Branchcircuit
conductors supplying household ranges, wall-mounted
ovens, counter-mounted cooking units, and other household
cooking appliances shall have an ampacity not less than the
rating of the branch circuit and not less than the maximum
load to be served. For ranges of 83∕4 kW or more rating, the
minimum branch-circuit rating shall be 40 amperes.

 

There are a fair number of 50A stoves and cooktops out there (breaker size listed in manufacturer instructions), so putting in wiring appropriate to 50A is good future proofing.

Breaker and whip may be 40A to simplify instruction of this specific stove without undue impact on a future upgrade later.

The stove demand factor from NEC is pretty sane. It's pretty hard to use 8.4kW while cooking at home, you need to be VERY fast and smart about it. Unless all you're doing is boiling massive pots of water.

 

The receptacle is 50 amps, so I would wire it as such. Allowing 40 amps is minimum requirement, but why do only the least required.

 

I agree on going above the minimum and future proofing (everything will be wired for 50 amp).
Just wish the manual text was written out more clearly and didn't have sections contradicting each other.

For example, the 12.9 kW nameplate rating / 240v = 53.75 amps. I'm assuming the 12.9 kW rating is based on when the range is maxxed out (all cooktop surfaces & oven on HIGH). The range elements also cycle on/off and I imagine it wouldn't be able to pull 53.75 amps long enough to exceed the breaker time vs. amp overage curve to trip. In other words, I see how a 50 amp breaker/wiring would be okay.

However, I don't see how NEC demand load would allow a 40 amp breaker, wiring, and cord and not run into the breaker tripping on a 53.75 amp range when every element is being used during a holiday cookout.

Even worse, per the demand load chart for 1 appliance, you could have a 16 kW rated range on a 40 amp breaker, 8 gauge wire, and 40 amp cord.
16 kW is 4 kW above 12 kW, which adds 20% demand load to their 8 kW max demand load for a single appliance.
That means a nameplate rating of 16 kW / 240v = 66 amps, but max demand load would allow for a 40 amp configuration (8 kW + 20% = 9.6 kW / 240v = 40 amps).
So you could have a 66 amp rated range on a 40 amp wiring setup.

I understand 99.9% of time you will never draw that rating or trip the breaker, but I would not be happy if everything is running full tilt on a holiday cookout and the breaker trips.

 

I assume the oven uses the maximum amount of power when doing a self-cleaning.

 

Not necessarily. Cleaning uses the same oven elements (power), just stay pon longer to higher temps. If you are cooking a big meal you are also using the top burners.

 

My plan right now is 50 amp breaker, 6/3 NM-b, and 50 amp appliance cord,

that is what i would do

no harm in having bigger wire

 

Yes, the rating is the sum of all elements. All elements go off and on to maintain a desired temp. The demand factor is an estimate of likelihood of how many will be on at any given time.
As to bake and broil elements being on at the same time: yes, they are during pre-heat. Some ranges do this automatically and some have a separate setting on the controls.

 

In my 50+ years in the trade I have only met one customer who had an issue with the range on a 40 amp breaker. The issue there was the breaker was old and weak--like me.... I just replaced the breaker and she never complain again about it tripping.

 

Had a similar headache with my range. Went down a rabbit hole trying to figure out breaker size and wiring when I installed my electric stove. The manual wasn't super clear either, so I was stuck between the 40 amp and 50 amp options like you.For mine, I ended up going with a 50 amp breaker, 6/3 NM-b wire, and a 50 amp cord. Even though the NEC calculations threw me off with that 8 kW number, I trusted the manual's suggestion for the cord size. The kW to Amps calculator came in handy when I was trying to double-check the amperage—super helpful for peace of mind.

 

<modern range is designed to be allowed on a 6/3, 50 with an 11/50 outlet. If a guy is replacing old this is a great time to change from 3 wire to 4.

 

You wouldnt have a 16KW on a 40 and it would be spec hard wired, not 50 outlet.

 

I do not ever recall an appliance that relied on the breaker for thermal,,, for its own cord or the wire in the wall for that matter. Not saying it couldnt or wont but its not designed that way.

 

It does have thermostats to prevent continuous operation and its not really heater or motor so not sure where 125% might apply???

 

Seems an oven can be sized at 100% due to thermostat best I recall but plug in appliance like a dryer is 24A on a 30 and I believe they size water heaters the same way. I have never threw a range wide open on a meter.
But if instructions say to use a 50 cord and outlet then it needs to be allowed to be plugged in to a legal 50 outlet. I believe you CAN put a smaller breaker on the circuit but couldnt make the appliance legal if it wasnt rated for 50A circuit. Similar to other cord and plug appliances, UL wont list a drill with a 15 end and require a 10A breaker. In fact has to be listed for use on a 20.

 

Been a while, someone fluent or just been thru code school would know but i believe this is the only exception outside of welder circuit allows wire/breaker exception to outlet rating???? Seems it said,,, outlet obviously dedicated to this appliance maybe???
Reason I remember is seems I have seen it and there is similar exception for a welder to use a 60 on the 50 outlet.

 

Reason I remember is seems I have seen it and there is similar exception for a welder to use a 60 on the 50 outlet.

There is no exception. The breaker can't exceed the outlet rating.

 

How hard are you going to work the range? Boiling 4 pots and broiling dinner?

This is an instance of where using the range in the upper end is going to rely on the thermal feature of the breaker.

 

The standard range has a 14-50 (not 11-50) cord and plug,
There are no such things as 40A plug or receptacle

 

Whoops, good catch, yes a 14. But unless it is under wired, breaker too small it wont likely open it, its really not intended to do that and not sposed to rely on it.

 

Seems I asked this question before and it went silent but when is the last time guys have seen a breaker open on a circuit of this type from thermal ? Memory is what it is but I can recall 4 faults of my own, 2 line to line and a couple ground faults. I have seen it from 2 heaters on a general circuit. (not mine) I remeber the faults over the last 30 years but cant recall a thermal on a single circuit.

 

My 7" angle grinder will open a 15A breaker on thermal. It needs a 20A circuit.

 

I will take it all back, come to think of it I had a 140 welder open one recent. Was during a test to see what we could wring out of it.

 

Yes there is for a welder. I will have to find it I sposed. As far as I know it's the only one in the book I always wondered how they could list 60 for a machine comes 50 end.

 

I will have to find it I sposed

If "Sposed" is meaning suppose we'd appreciate that. Thanks!

 

Reason I remember it is argued the point too till some old timer pointed it out.