Wall oven whip too small?

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S'mise

Senior Member
Location
Michigan
I'm installing a new 7.4kw wall unit range. 30.8a @240v.
Manufacture says minimum circuit size is 40 amps.
So, I've installed a 40a breaker with #6 aluminum for branch ckt.

What alarms me is the factory installed whip that came with it is #10 with a 12awg neutral.

I can't recognise what insulation type these conductors are but assuming 75c terminations 10awg is only rated for 35 amps. Why would manufacture want to use wire smaller than the 40a ocpd can protect?

What am I overlooking? Is this ok because it's a ul approved assembly?

Also, Am I required to derating for ambient temperature since jbox is behind the range?
If so, how do you determine what temp to use?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Yes, you can basically ignore the manufacturer's issues as an assembly, and the load is considered non-continuous. The #6 was overkill; I probably would have run #10cu or #8al.
 

Buck Parrish

Senior Member
Location
NC & IN
Yes, it's okay, like you said It's been UL approoved and tested. No
ambient temperature
required behind the stove.

The main thing we get service calls on is if the AL is not connected good to the CU wires, it heats.
 

S'mise

Senior Member
Location
Michigan
Thank you for clarification. The idea of #10 on the 40a breaker alarmed me, but I guess it's the same as how they use zip cord (20awg) on a lamp that's plugged into a 20a outlet. The ul rating has deemed it safe, or at least mostly safe.

My mistake, I actually did use #8 al. Now, had I used the 80% demand factor per table 220.55 I could have to rduced the wire size but I'd have to also reduce the breaker size.
Probably not an option because a min 40a ckt. was specified in the instructions.

Thanks again, I think I'll be able to sleep tonight.
 

S'mise

Senior Member
Location
Michigan
What is a wall unit range? Do you mean cooktop? or is this a range top with oven?

It's a double wall oven with upper and lower doors. Sorry, Range wasn't an accurate description.

So, Let me understand this;
Had I installed the whip with #10, it'd be a violation. But since it came out of the box with the whip installed, it's ok because its a UL listed unit?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
It's a double wall oven with upper and lower doors. Sorry, Range wasn't an accurate description.

So, Let me understand this;
Had I installed the whip with #10, it'd be a violation. But since it came out of the box with the whip installed, it's ok because its a UL listed unit?

Yes. If the kw rating were 8.75 kw or larger then the NEC would mandate a 40 amp circuit. If not for the wording in the instructions you could use a smaller branch circuit.
 

S'mise

Senior Member
Location
Michigan
Yes. If the kw rating were 8.75 kw or larger then the NEC would mandate a 40 amp circuit. If not for the wording in the instructions you could use a smaller branch circuit.
Yes I understand that, but since the manufacture stipulates a min 40a breaker I'd expect the whip to be #8 to follow suit.

The oven itself (Frigidaire) is obviously ul listed, but I hadn't considered that the whip (made by another manufacture) is also a part of this oven listing.
Who's to say I didn't use my own whip with the wrong wire?

I dont mean to belabor the point, but it seems strange to me. If there happens to be a short circuit in the oven, that #10 whip can potentially melt by the time the 40a breaker clears it.

Anyway, if its good enough for the UL, it should be ok with me.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Yes I understand that, but since the manufacture stipulates a min 40a breaker I'd expect the whip to be #8 to follow suit.

The oven itself (Frigidaire) is obviously ul listed, but I hadn't considered that the whip (made by another manufacture) is also a part of this oven listing.
Who's to say I didn't use my own whip with the wrong wire?

I dont mean to belabor the point, but it seems strange to me. If there happens to be a short circuit in the oven, that #10 whip can potentially melt by the time the 40a breaker clears it.

Anyway, if its good enough for the UL, it should be ok with me.

A 40 amp circuit would have only a #10 EGC so I don't see how the same #10's as phase conductors would melt. I understand your point but IMO you're overthinking this. Also the whip comes with high temperature conductors which have an ampacity likely well above the 30 amps for a standard #10 THHN conductor.

The whip came on the unit, the instructions say use a 40 amp circuit is there more to it than that?
 

S'mise

Senior Member
Location
Michigan
A 40 amp circuit would have only a #10 EGC so I don't see how the same #10's as phase conductors would melt. I understand your point but IMO you're overthinking this. Also the whip comes with high temperature conductors which have an ampacity likely well above the 30 amps for a standard #10 THHN conductor.

The whip came on the unit, the instructions say use a 40 amp circuit is there more to it than that?
The whip has only #12 egc but I agree that I'm over thinking this.
If the conductors are 90c rated they can handle a full 40a.

Thanks for your advice, I feel much better about it.
 

kwired

Electron manager
Location
NE Nebraska
The whip has only #12 egc but I agree that I'm over thinking this.
If the conductors are 90c rated they can handle a full 40a.

Thanks for your advice, I feel much better about it.
I bet they are at least 125C conductors, then many other things that have already been mentioned come into play - especially the fact this will not draw full rated current for any extended amount of time, once oven reaches set point it will cycle as needed to maintain temp.
 

S'mise

Senior Member
Location
Michigan
I bet they are at least 125C conductors, then many other things that have already been mentioned come into play - especially the fact this will not draw full rated current for any extended amount of time, once oven reaches set point it will cycle as needed to maintain temp.
I'll take a closer look at the wire type tomorrow. I didn't recognize the usual letters signify the insulation type.
At least for a while, it should draw flc if both ovens are preheating or in cleaning mode.

But I do get the importance of the high temp wire and why UL would pass it.

I guess I'm just too used to using thhn wire.
 
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