Manufacture violating NEC

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hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
Hooking up a new double oven today at one of our sales guys house, the exsisting wiring was #10, the new oven is a 9kw, manufacture calls for 40 amp ocp. With this being a 37.5 amp load, a 40 amp breaker and circuit will not meet NEC minimum breaker size. Do I violate the NEC with a 40 amp breaker? or do I violate the manufactures instructions with a 50 amp breaker?
 

slick 50

Senior Member
37.5 is the max load if you were to have all burners and oven on at the same time which is unusual but the 40 amp breaker is sufficent since an oven is not a continuous load. You will need to change wire to #8 though.
 

iMuse97

Senior Member
Location
Chicagoland
The oven is a double oven, so the manufacturer does their own load calculations. The result: use the 40A OCPD and #8 awg. BTW, (to Slick), there are generally no "burners" of the type you were referring to on an oven. :)
 
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mcclary's electrical

Senior Member
Location
VA
The oven is a double oven, so the manufacturer does their own load calculations. The result: use the 40A OCPD and #8 awg. BTW, (to Slick), there are generally no "burners" of the type you were referring to on an oven. :)

Oh yeah? reach in and touch one, and come back and tell me if you're willing to call it that:grin:
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
Since it is a double oven, both ovens on simultainiously would not be uncommon. Once up to operating temperature, the load would cycle off and on, but the full load is known to excede 80% of the breaker rating for a fair amount of time. The 40 amp ocp by code would hold, since it is supposed to carry 100% of its rating indefinetly. Another one of those who do you believe? The NEC or the manufacture. ( by the way it was a royal pain replacing the exsisting wire, sheetrock ceiling in the basement with the nearest open access in a unfinished bedroom 16' away. Made it happen though without cutting the first piece of rock!)
 

LJSMITH1

Senior Member
Location
Stratford, CT
In this case, with a legitimate question, why can't someone just call the manufacturer to get clarification or confirmation? You can guess all day long as to what is an error or not...:roll:
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
In this case, with a legitimate question, why can't someone just call the manufacturer to get clarification or confirmation? You can guess all day long as to what is an error or not...:roll:

The manufacture is an expert on the NEC?:roll: Someone at the manufacture tells you one thing, without it being in writing, then the insurance company lawyers ask why you did not follow the NEC when something happens. I have found that even if an onsite engineer tells you to do something, you better get it in writing if there is any question at all about the legality.
 

pfalcon

Senior Member
Location
Indiana
Mfg instructions are supposed to be established by actual testing of the device. Therefore they are the optimal requirements. They supercede the NEC requirements when used as listed.

If you go lower then you have to prove the drop; which the NEC won't support.
If you go higher on the OCPD then you risk equipment damage when it doesn't trip soon enough.
 

LJSMITH1

Senior Member
Location
Stratford, CT
The manufacture is an expert on the NEC?:roll: Someone at the manufacture tells you one thing, without it being in writing, then the insurance company lawyers ask why you did not follow the NEC when something happens. I have found that even if an onsite engineer tells you to do something, you better get it in writing if there is any question at all about the legality.

Of course they are an expert in their OWN product - which they designed to meet NEC requirements when installed in a particular manner! :roll:

Call the Mfr. You talk directly to a product manager or engineer. Take their name down. If they tell you something different than what is already defined in the instructions, politely ask them to put it in writing and email it to you. If they won't, then they cannot backup what they are telling you, so don't deviate from the installation instructions. Don't over complicate it. Keep it Simple.

Mfr. Reps are not going to know or do they care about this kind of question. They sell product, not answer questions that they think are already addressed in the installation manual.:)
 

LJSMITH1

Senior Member
Location
Stratford, CT
Mfg instructions are supposed to be established by actual testing of the device. Therefore they are the optimal requirements. They supercede the NEC requirements when used as listed.

If you go lower then you have to prove the drop; which the NEC won't support.
If you go higher on the OCPD then you risk equipment damage when it doesn't trip soon enough.

Very Good. :)
 

iwire

Moderator
Staff member
Location
Massachusetts
OK, so the manufacture can lower the standards the NEC sets, but local muni's can't. It's all clear now!:roll:

Kind of like that, the real difference is the manufacturers work goes though testing and listing to prove it is safe as designed.

On the other hand our work in the field is not really tested so the NEC standards are going to be on the conservative side.

On another note,

With this being a 37.5 amp load, a 40 amp breaker and circuit will not meet NEC minimum breaker size.

The NEC allows a 40 amp breaker to carry 37 amps for up to 3 hours at a time. There is no way that unit will ever draw 37 amps for more than 3 hours continuously
 

skeshesh

Senior Member
Location
Los Angeles, Ca
OK, so the manufacture can lower the standards the NEC sets, but local muni's can't. It's all clear now!

I dunno, I'm with pfalcon on this one. The NEC has to address such a grand range of issues that it's requirements and recommendations can't help but contain inaccuracies. The mfg. requirement may look lower numerically, but they may provide the more stringent protection.
 
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Smart $

Esteemed Member
Location
Ohio
...
On another note,

with this being a 37.5 amp load, a 40 amp breaker and circuit will not meet nec minimum breaker size.

the nec allows a 40 amp breaker to carry 37 amps for up to 3 hours at a time. There is no way that unit will ever draw 37 amps for more than 3 hours continuously

40A @ 80% = 32A

Sidenote: something funky going on here... prior to adding this line, I kept entering "A" for amperes and the board kept changing it to "a"... until I added more text :confused:
 
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mivey

Senior Member
40A @ 80% = 32A

Sidenote: something funky going on here... prior to adding this line, I kept entering "A" for amperes and the board kept changing it to "a"... until I added more text :confused:
40*100%=40. And 40 > 37 (the OP value)

add: Just noticed the OP value was 37.5A
 

mivey

Senior Member
Sidenote: something funky going on here... prior to adding this line, I kept entering "A" for amperes and the board kept changing it to "a"... until I added more text :confused:
I was able to enter A
Even 32A
Not sure what was going on
 
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