Oven

ritelec

Senior Member
Location
Jersey
hmmm... leave the 6's on the 50 amp. screw a panel to the back of the oven and feed the panel with that, then feed the oven with 8's on a 40 amp with a 10 ground. (kidding)

thank you for bringing this up. truly
 

hillbilly1

Senior Member
Location
Atlanta,Ga
I think the upsizing was put in where the conductor is upsized for voltage drop, then the egc would require upsizing for the same reason. That would not be the case here, but then code reads like a law book! LOL!
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
The #12 part is correct but the #8 to #6 is not for a 40 amp circuit. Since you start with a 40 amp circuit and a #8 phase conductor by using a #6 for the same 40 amp circuit you have increased the size of the phase conductor therefore you must also proportionately increase the size of the EGC. So if the #8 AWG cable has a #10 EGC and the #6 AWG cable has the same #10 EGC you cannot use the #6 cable for the 40 amp circuit because you have not increased the size of the EGC (both cables have a #10 EGC). The proportionate increase in the EGC would be the same ration as the increase from #8 to #6.

As I said previously DUMB...
Yes I get that.. what I was saying is that in the case above going from a #8 wire on a 40 amp cir with 10 equipment grounding conductor to a #6 wire on a 40 amp circuit would require a #6 equipment grounding conductor. It doesn't make sense.

And I love the fact that if I put the #6 on a 50 or possibly 60 amp breaker then I only need a #10 equipment grounding conductor.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
You haven't upsized the circuit, you've downsized the oven!;)
Plus I doubt anyone would pull a permit for a job like this. Our inspectors would have a fit if they had to come look at a breaker change.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Yes I get that.. what I was saying is that in the case above going from a #8 wire on a 40 amp cir with 10 equipment grounding conductor to a #6 wire on a 40 amp circuit would require a #6 equipment grounding conductor. It doesn't make sense.
I didn't do the math but if you had a 40 amp circuit with a #8 ungrounded conductor and went to a #6 ungrounded conductor the EGC would increase from a #10 to a # 8 not a #6.
 

kwired

Electron manager
Location
NE Nebraska
I think the upsizing was put in where the conductor is upsized for voltage drop, then the egc would require upsizing for the same reason. That would not be the case here, but then code reads like a law book! LOL!
VD is the reason for the rule. It is worded as one size fits all type of thing and makes for unnecessary required increase in some instances where same size EGC covers a range of OCPD's in T250.122 and voltage drop is not a concern, espcially when using cable wiring methods where you only have on size EGC commonly found in certain cables as related to the insulated conductors.10 thru 6 insulated cables will typically have 10 AWG grounding conductor.
 

StarCat

Senior Member
Location
Moab, UT USA
Growler, one time many years ago I was repairing a " Subzero " refrigerator in a residence. The owner was both offended that the system was broken, and that they had to actually pay something to have it fixed. About one year before I walked away from a service truck, I was doing Commercial-Industrial work only as the residential thing had gotten fully ridiculous and totally distasteful.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
True, but irrelevant. :happyno: You would still need to upsize the EGC. The rule says that if you increase the size of the ungrounded conductors (with "increased" having been explained in the 2017 edition as meaning beyond the minimum ampacity requirements), then you increase the EGC proportionally.
Wait, what are we talking about? You only have to up-size if for voltage drop.
 

wwhitney

Senior Member
Location
Berkeley, CA
By definition of AWG, the ratio of #10 / #8 = the ratio of #8 / #6, the system follows a geometric progression.

And in that statement I didn't need to specify whether I mean diameter ratio or area ratio, as the two are equivalent.

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
If you claim that the cable pases through an area with ambient temperature of 31 C (88 F), then for 60C conductors a 0.91 temperature correction factor applies to the ampacity. That means that a #8 conductor is no longer adequate for a 40A load, meaning that #6 is the smallest size allowable. In which case the ungrounded conductors have not been increased in size, and there is no problem with EGC size.

Cheers, Wayne
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Wait, what are we talking about? You only have to up-size if for voltage drop.
There was a time when the NEC did limit the need for upsizing the EGC to instances when the ungrounded conductors were increased because of VD considerations. But I think there was a bit of abuse going on, as in, "I didn't use the larger wire because of VD. It was just what I had in the truck at the time." The rule was changed to require upsizing the EGC regardless of the reason that the ungrounded conductors were upsized. The oldest code book I have handy is 2008, and this change happened before then.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
That means that a #8 conductor is no longer adequate for a 40A load, meaning that #6 is the smallest size allowable. In which case the ungrounded conductors have not been increased in size, and there is no problem with EGC size.
I may have had some influence in getting that clarification into the NEC. For several cycles, I sent in update recommendations that pointed out that the statement, "increased in size" means nothing, unless you clarify by stating "increased from what?" It now says "increased in size from the minimum size that has sufficient ampacity for the intended installation." So your example fits perfectly into the current language.
 
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