200amp (3/0) power feed

[Joshua5438]

I am installing a meter can and main panel on a metal building. This will be a 200amp service so I will be using 3/0 cu wire. I had originally planned to mount my main panel directly behind my meter can on the inside of my exterior wall. Feed the wire through a 2" nipple between the two panels. In searching I have realized that this is against code based on 312.6 (unless I am reading it wrong). If I am correct, how else can I feed my main panel? I am guessing I will have to use a top or bottom exit from the meter can instead of a back exit? How would I feed the cable into the building and could I use a back feed in the main panel or would I need to come in from the top or bottom also? I am having a hard time picturing my options.

 

[wwhitney]

Is this building a non-dwelling unit? For a dwelling unit service you can use the 83% rule. And I see SC is still on the 2017 NEC; for the 2020 NEC a dwelling unit would require an outdoor emergency disconnect

Anyway, I believe you are reading 312.6 wrong, as I understand the install you initially described is very common. What exact 312.6 violation do you see?

Cheers, Wayne

 

[Sponsor]

 

[Joshua5438]

This is not a dwelling so I am wanting the full 200amp service. This will be a separate building for a shop.

I was reading that 312.6 states a deflection of conductors rule. I am trying to figure it out myself. I was reading that if you go more than a 2/0 you are not allowed to feed through the back of the can as it creates to much of a bend in the wire. I sure I am reading it all wrong as this has been my plan all along.

 

[wwhitney]

I think the wire bending space provisions in 312.6(B)(1) (which would apply when wires are leaving the back of the cabinet) refer to the distance from the terminal to the side of the enclosure. So your meter socket and your panel that have lugs listed for 3/0 should have those lugs at least 4" away from the sides and top and bottom of the enclosure. Distance to the front and back of the cabinet is not regulated by that language.

At least that's my understanding.

Cheers, Wayne

 

[Joshua5438]

That's what I hope but what about the distance from the lug to the edge of the nipple in the back that connects the meter can to the main panel?

 

[Joshua5438]

This is my box and one that I came across that failed inspection.

 

[wwhitney]

Nothing in 312.6 discusses the distance from the lug to the conduit opening. Just the distance from the lug to the wall of the cabinet that is at the bottom of your picture. Which is certainly above 4" when measure along the line of the lug entry. I don't see any 312.6 issue.

Cheers, Wayne

 

[Joshua5438]

Thanks and I agree. The inspector on that panel said the conduit fell under obstructions and that panel was 3 5/8 from lug to conduit. Could I use a 2.5" conduit from meter to main with no issues? This would give me right at 4" so if it is an issue this should cover it. I will be feeding (3) 3/0 wires through it.

 

[Joshua5438]

What are your thoughts on this? This was a change to the NEC in 2014.

(C)
Back Wiring Space. Where a raceway or cable entry is in the wall of the enclosure opposite a removable cover, the distance from. that wall to the cover shall be permitted to comply with the distance required for one wire per terminal in Table 312.6(A). The distance between the center of the rear entry and the nearest termination for the entering conductors shall not be less than the distance given in Table. 312.6(B).

 

[wwhitney]

South Carolina is under the 2017 NEC, and I don't see that language there. What is the full citation?

Also, are you now saying that you have an inspector that is failing your installation similar to the second picture, based on measuring from the lug to the conduit hole in the back? Table 312.6(A) Note 1 says "1. Bending space at terminals shall be measured in a straight line from the end of the lug or wire connector (in the direction that the wire leaves the terminal) to the wall, barrier, or obstruction" As a straight line from the end of the lug in the direction the wire leaves does not hit the conduit entry, I find illogical and indefensible to call the location of the conduit entry an "obstruction" in that context.

But if your inspector is calling it an obstruction, then I'm not quite sure how to rebut that. I guess I would just show that a 4" straight section of wire can be sticking out from the lug unobstructed. Nothing 312.6 actually regulates how the wire is installed or how the wire is bent. There are no bending radius requirements for individual conductors for under 1000V in the NEC, to my knowledge.

I.e. compliance with Table 312.6(A) can be judged before the wires are installed, and doesn't depend on the wire routing.

Cheers, Wayne

 

[wwhitney]

P.S. It is worth contrasting the language in 314.28 with the language in 312.6. The former explicitly regulates the distance between conduit entries, while the latter does not. If 312.6 was trying to regulate distance from lug to conduit entries, it would use language similar to 314.28.

The meter enclosure falls under Article 312, not Article 314, so 314.28 does not apply.

Cheers, Wayne

 

[Joshua5438]

I am honestly just piecing it together. I did not see that in the 2017 code but figured I would bring it up as it popped up with my searches.

I have not been failed but that second picture was someone that did fail an inspection. I am still waiting on my building to be completed so I can get the panels installed. Just trying to be proactive and sort through everything.

I do not feel I will fail inspection as I see this many times in my area but it's typically with 2/0 and not 3/0 feed. I figure it's best to ask around and see what others have experienced and change my game plan if need be before I get started. If I were to fail I am not sure how I would go about changing it up to pass. Guess I would have to come up with a bottom exit and then figure out how to get that into the building and into the main panel.

 

[wwhitney]

OK, well my opinion is obviously that the last picture does not violate 312.6, as that section does not discuss conduit entries like 314.28 does. Also a conduit entry is not an obstruction, as a 4" straight piece of wire can still stick out of the lug. Good luck.

Cheers, Wayne

 

[Joshua5438]

That makes me feel better about the distance issue. I know a lot is up to interpretation at the end of the day. I see no issue with this install as it give plenty of room for the bend from lug to conduit.

 

[Joshua5438]

OK, well my opinion is obviously that the last picture does not violate 312.6, as that section does not discuss conduit entries like 314.28 does. Also a conduit entry is not an obstruction, as a 4" straight piece of wire can still stick out of the lug. Good luck.

Cheers, Wayne

Thanks again!

What are your thoughts on the size of conduit to connect the two boxes? I am thinking 2.5" as that's the max size hole my main panel allows in the center of the back. I believe 2" is typical for (3) 3/0 wires but is larger ok?

 

[wwhitney]

Larger on conduit is (almost) always fine. There is something to be said for using a non-metallic (PVC) conduit between the meter base and the service panel, as it avoids a parallel neutral path. NEC Appendix C has tables for the the maximum number of conductors, all of the same size, within most any size conduit.

Cheers, Wayne

 

[Joshua5438]

So you recommend pvc over metal conduit? I wasn't sure if either is preferred as both panels will be bolted to the steel structure. Do I need to isolate either panel from the building?

 

[wwhitney]

If both panels are bolted to the steel structure, then PVC vs steel conduit is moot. There's an argument for making sure the service mast/underground conduit and meterbox are isolated from the building steel (bonded only to the service neutral) and using PVC conduit to the indoor service panel. Then all neutral current will return on the neutral service conductor. But if that's too much trouble, it's fine to do everything in steel and bolt everything to the building frame, very common and nobody worries much about it.

Cheers, Wayne