Feeder sizing

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crtemp

Senior Member
Location
Wa state
Does table 310.15(b) apply to a feeder to a shop? I wasn't sure if it only applies to dwelling units. Basically just need to know if 1/0 urd is good for a 125 amp feeder to the shop. The shop is located at a dwelling it's just detached from it.
 

iwire

Moderator
Staff member
Location
Massachusetts
Does table 310.15(b) apply to a feeder to a shop? I wasn't sure if it only applies to dwelling units. Basically just need to know if 1/0 urd is good for a 125 amp feeder to the shop. The shop is located at a dwelling it's just detached from it.

It does not apply to a detached shop.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor


Since the garage load is part of the service then the house does not carry the entire load. This is how I see it and was also how some of the cmp members saw it when specifically asked that question. Why would a detached garage be different than an attached garage. The function of Table B(7) is diversity so it seems that the garage should be considered as part of the homes diversity detached or attached
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Since the garage load is part of the service then the house does not carry the entire load. This is how I see it and was also how some of the cmp members saw it when specifically asked that question. Why would a detached garage be different than an attached garage. The function of Table B(7) is diversity so it seems that the garage should be considered as part of the homes diversity detached or attached

That sounds like one my my hair-brained ideas :D
Lets see... I build my house with an attached garage and I use the Table.
I build the exact same house wit the exact same garage load but the garage is detached across a 3' walkway and I can't use the Table.
makes sense to me :D same logic as feeding your A/C load from your meter combo so you have to use a bigger feeder to the inside panel
 

Dennis Alwon

Moderator
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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
May I ask why you say it can't be used on a residence?


It can be used on a residence but IMO, not in the example stated since the house will have a feeder that does not carry the entire load. If you look at art. 310.15(B)(7)-- not the table but the article -- 2008 it is (B)(6) it states all loads that are a part or associated with the dwelling.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Sorry I have been multi tasking. In order for a feeder to be allowed to use the residential T. 310.15(B)(7) or B(6) for the 2008 the feeder must carry the entire load of the dwelling or associated with the dwelling. Since the garage is associated and has a separate feeder then the dwelling cannot use this table for the feeder.

Does that make sense?
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Sorry I have been multi tasking. In order for a feeder to be allowed to use the residential T. 310.15(B)(7) or B(6) for the 2008 the feeder must carry the entire load of the dwelling or associated with the dwelling. Since the garage is associated and has a separate feeder then the dwelling cannot use this table for the feeder.

Does that make sense?


But that is Dennis' opinion. I personally would ask the AHJ. I can't disagree with Dennis' logic, but the local AHJ may interpret differently. OTOH if it were my house you would not use that table.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
But that is Dennis' opinion. I personally would ask the AHJ. I can't disagree with Dennis' logic, but the local AHJ may interpret differently. OTOH if it were my house you would not use that table.

Ah, man you hurt my feelings....:D It is an opinion but it seems clear when they say all loads associated with the dwelling. I guess one could say that the garage isn't associated with the dwelling but it really is-- yes that's my opinion. Not sure it makes sense otherwise.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Not sure that any of the discussion of that table is relevant. #1/0 AL is already rated at 120 amps, next size up is 125 amps.
 

iwire

Moderator
Staff member
Location
Massachusetts
Since the garage load is part of the service then the house does not carry the entire load. This is how I see it and was also how some of the cmp members saw it when specifically asked that question.

The service conductors would still be carrying 100% of the dwelling unit load.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The service conductors would still be carrying 100% of the dwelling unit load.


Do you mean dwelling or the dwelling and associated loads???? Yes the service conductors would qualify but not the feeders to the house and garage, IMO
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Maybe you know something I do not but the OP never mentioned a feeder to the house.
There may not be a feeder to the house. I brought it up as if there were a feeder to the house panel and stated that it could not use the resi table because of the garage. I was just adding some extra info. Certainly the service conductors are fine using the table.
 
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