conductor sizing for sub-panel

[steelersman]

I'm going to be running a circuit out to a detatched garage for a 100 amp sub-panel. I'm going to use 4 conductor USE aluminum for the feeder underground (2 hot legs, a neutral, and a seperate ground). Can I use #2 Al for my feeder per section 310.15(B)(6) or do I have to use #1 Al per 310.16?

 

[Pierre C Belarge]

Table 310.16

 

[infinity]

310.15(B)(6) is for dwellings, not a detached garage so that's out of the mix. You'll need to use 310.16 for the conductor sizing. USE cannot enter the building 338.12(B).

 

[chris kennedy]

I'm going to be running a circuit out to a detatched garage for a 100 amp sub-panel. I'm going to use 4 conductor USE aluminum for the feeder underground (2 hot legs, a neutral, and a seperate ground). Can I use #2 Al for my feeder per section 310.15(B)(6) or do I have to use #1 Al per 310.16?

I'll go with 310.16.

Section 310.15(B)(6) permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6). For the 2008 Code, the panel clarified that this permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load.

 

[steelersman]

ok thanks for the help. I agree 310.16 is the winner.

Now what I need help with is since I don't have a copy of the 2005 NEC (which is what I'm working under for this), is table 310.16 the same in the 2005 and 2008 codebooks for #1 Al USE (100 amps)?

 

[steelersman]

USE cannot enter the building 338.12(B).

I see that in the 2008 book. However since it is shaded that means it is new for 2008 right?

If so then since i'm working under 2005 then it should not be a problem to have my USE terminate in the sub-panel which will be just on the inside of an exterior wall.

 

[Greg1707]

breaker and conductor

breaker and conductor

Is not the real issue matching the size of the breaker in the main panel to the size of the conductor to the sub panel? Couldn't you use a 30 amp breaker and #10 cable?

 

[Dennis Alwon]

I see that in the 2008 book. However since it is shaded that means it is new for 2008 right?

If so then since i'm working under 2005 then it should not be a problem to have my USE terminate in the sub-panel which will be just on the inside of an exterior wall.

USE unless it is dual rated cannot enter a building even in the 2005.

 

[steelersman]

Is not the real issue matching the size of the breaker in the main panel to the size of the conductor to the sub panel? Couldn't you use a 30 amp breaker and #10 cable?

yes i could use a #10 Cu conductor with a 30 amp breaker if that's all the customer wanted. However since she wants a 100 amp panel, a #10 conductor isn't good enough. So I'll use #1 Aluminum USE instead.

 

[steelersman]

USE unless it is dual rated cannot enter a building even in the 2005.

Could you explain to me why that section is shaded then in the 2008? It is my understanding that the shaded areas are new or additions to the new code.

 

[chris kennedy]

Could you explain to me why that section is shaded then in the 2008? It is my understanding that the shaded areas are new or additions to the new code.

There was no 338.12 in the 05.

 

[Dennis Alwon]

Could you explain to me why that section is shaded then in the 2008? It is my understanding that the shaded areas are new or additions to the new code.

I believe it was moved from the section "uses permitted" to where it was more appropriate "use not permitted". It was in 338.10(A)

 

[steelersman]

I believe it was moved from the section "uses permitted" to where it was more appropriate "use not permitted". It was in 338.10(A)

Ok so I can't enter the building with the USE according to the 2005 NEC also? Even though it's just going straight into the back of the panel?

 

[stickboy1375]

Ok so I can't enter the building with the USE according to the 2005 NEC also? Even though it's just going straight into the back of the panel?

Usually it does not contain a flame retardant jacket, so it cannot enter the structure. I generally use XHHW.

 

[steelersman]

Usually it does not contain a flame retardant jacket, so it cannot enter the structure. I generally use XHHW.

Yeah I was trying to avoid a disconnect on the outside of the garage. I was also trying to avoid conduit in the ground. I wanted to use USE and come up out of the ground with pvc and use an LB and go right into the back of the panel (main breaker for disconnect). I guess technically the way to do it is to use a disconnect on the outside first, then go into the panel (which could now be main lug) with XHHW insulated conductors. And still use my USE conductors underground and up to the line side of disco.

 

[steelersman]

Usually it does not contain a flame retardant jacket

right. It actually has no jacket at all for that matter.

 

[infinity]

Yeah I was trying to avoid a disconnect on the outside of the garage. I was also trying to avoid conduit in the ground. I wanted to use USE and come up out of the ground with pvc and use an LB and go right into the back of the panel (main breaker for disconnect). I guess technically the way to do it is to use a disconnect on the outside first, then go into the panel (which could now be main lug) with XHHW insulated conductors. And still use my USE conductors underground and up to the line side of disco.

That would be one way of doing it or you could install a junction box on the outside instead of the LB and transition in there.

 

[steelersman]

That would be one way of doing it or you could install a junction box on the outside instead of the LB and transition in there.

I think I may go that route. Thanks.

 

[Dennis Alwon]

I think I may go that route. Thanks.

Check your cable first and see if it is dual rated. It may be okay to use in the structure.

 

[steelersman]

Check your cable first and see if it is dual rated. It may be okay to use in the structure.

Dennis what would it say? What do you mean by dual rated?
I haven't purchased the wire yet so maybe I should buy dual rated?