all branch circuits go into panel via 2" PVC, 310.15(B)(3)(a) issue ?

RustyShackleford

Senior Member
Location
NC
I'm looking at doing a main panel replacement, where ALL the branch circuits enter the panel via an L-shaped section of PVC conduit that brings the conductors in from the crawlspace, into the bottom of the exterior panel enclosure. The panel has 16 single-pole breakers and 5 double-pole ones, hence I'm counting over 41 current-carry conductors and thus a de-rating to 35% of the non-adjusted allowable currents in the conductors.

Is this a code or safety concern ? It's a close call whether the conductors are enclosed for more than 24". They are bundled together (in the crawlspace) as they enter the PVC, and then the PVC itself is perhaps18" long. So it depends upon how you count the PVC elbow (center-line, or outside of curve), and to what extent the bundling, before entering the PVC, counts against the 24". Seems like maybe this should be pretty strictly applied, given the fact we're talking a 35% de-rating factor.

It certainly makes the panel replacement a bit easier though - no messing with multiple knockouts and clamps ...

Thoughts ?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I agree with Bob above. Unless you have tie wrapped the cables there really is no bundling issue. If you run thru the lb and conduit is 24" or less than don't worry about de-rating. Even then you have the except below to fall back on

(2) Selection of Ampacity. Where more than one ampacity
applies for a given circuit length, the lowest value shall be used.
Exception: Where different ampacities apply to portions of a circuit, the
higher ampacity shall be permitted to be used if the total portion(s) of
the circuit with lower ampacity does not exceed the lesser of 3.0 m
(10 ft) or 10 percent of the total circuit.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Are these conductors or cables? If cables there is a 312.5(C) issue.
Agreed. Is there a simple solution to comply with 312.5(C) while maintaining the 18" of PVC?

The obvious idea that occurs to me is to put a short section of wireway or large junction box on the open end of the PVC, and then bring the cables into the wireway/box via multiple entries with cable clamps. Then you'd need to confirm that the fill on the PVC nipple does not exceed 60%.

Or could you just throw a large screw mount cable tie around all the cables where they emerge into the panel, and secure the cable tie to the back of the enclosure? : - )

Also, if the PVC conduit is exposed on the outside of the structure and the cable is NM cable, that's a violation for NM cable in a wet location.

Cheers, Wayne
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Agreed. Is there a simple solution to comply with 312.5(C) while maintaining the 18" of PVC?

The obvious idea that occurs to me is to put a short section of wireway or large junction box on the open end of the PVC, and then bring the cables into the wireway/box via multiple entries with cable clamps. Then you'd need to confirm that the fill on the PVC nipple does not exceed 60%.

Or could you just throw a large screw mount cable tie around all the cables where they emerge into the panel, and secure the cable tie to the back of the enclosure? : - )

Also, if the PVC conduit is exposed on the outside of the structure and the cable is NM cable, that's a violation for NM cable in a wet location.

Cheers, Wayne
There is no simple code compliant rule for this installation. The only provision for the use a raceway with multiple cables in it is in the exception to 312.5(C) and that only permits the raceway to extend vertically from a surface mount panel.
 

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
Sounds like you have cable’s unless there all UF, how you going to put nmb in exterior conduit. If it’s piped and you have thwn then, Never mind but I don’t read it that way.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
There is no simple code compliant rule for this installation. The only provision for the use a raceway with multiple cables in it is in the exception to 312.5(C) and that only permits the raceway to extend vertically from a surface mount panel.
A couple comments:

1) The only issue with putting multiple cables with a sleeve into a conduit into a panel is the requirement you cited of 312.5(C) "Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure." The exception is an allowance to skip securing the cables to the panelboard cabinet, but if you can figure out how to secure the cables to the cabinet, you can certainly bring the cables in via a sleeve that doesn't comply with the long list of requirements in the exception (such as the sleeve described in the OP).

The standard way to secure a cable to the cabinet is via a cable clamp in a KO. But surely there are other ways to secure cable to a cabinet, and some of those ways might be compatible with many cables emerging through a single KO. The screw mount cable tie I suggested seems pretty flimsy, but why shouldn't that be considered "securing"?

2) Presumably 312.5(C) does not disallow the use of a cable wiring method within a complete conduit system, where conductors or cables are not secured to enclosures. So if you secure the cables to another enclosure, and provide a complete conduit system between that enclosure and the panelboard cabinet, then the cables don't need to be secured panelboard cabinet. Hence my suggestion of a box or wireway where the cables can be secured with multiple entries and multiple cable clamps, and that the conduit would have to comply with the fill requirements, since it is no longer a sleeve.

Cheers, Wayne
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
In the south this is done all over the place. I used to do it myself. No...it is not allowed per code however it was accepted as the best alternative to getting wiring into an outdoor panel.

Then the code changed where nm wasn't allowed in conduit outdoors so NC made an amendment to allow up to 6' of nm to be sleeved in conduit outdoors.

I really have never seen a safety issue with it.
 

RustyShackleford

Senior Member
Location
NC
I believe it's all NM-B. And yes, the conduit comes out of the crawlspace (to the outside) thru an LB (not a simple elbow as I said in OP) and up a few inches into the outdoor-rated main breaker panel. There is no NM-B exposed to the outside. Sounds the amendment that Dennis quoted above (post #9) covers me there.

Re. 312.5(C), the Romex is all stapled to wood framing in the crawlspace shortly before entering the conduit; it is not secured in any way as it leaves the conduit inside the panel.

Another issue is conduit fill: since NM doesn't appear in the tables, I believe you have to calculate based on cross-sectional area. However, is it not true that short runs of conduit used for "protection" are not subject to conduit fill limits ?

BTW, replacement is because it's a Federal Pacific panel, but that's a whole 'nother discussion ...
 
Last edited:

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
I believe it's all NM-B. And yes, the conduit comes out of the crawlspace (to the outside) thru an LB (not a simple elbow as I said in OP) and up a few inches into the outdoor-rated main breaker panel. There is no NM-B exposed to the outside.
If the job is in NC, then I recall reading here that NC has an amendment that allows up to 6' of outdoor conduit with NM in it, in which case the above is fine. In the unamended NEC, the above would be a violation, because 300.9 says the interior of the exterior conduit is a wet location, so NM cable is not allowed.

Re. 312.5(C), the Romex is all stapled to wood framing in the crawlspace shortly before entering the conduit; it is not secured in any way as it leaves the conduit inside the panel.
Unless the conduit meets all the requirements of 312.5(C) Exception, the cables would still need securing to the cabinet, and stapling them just outside the sleeve is not sufficient. And the installation described does not meet all the requirements of 312.5(C) Exception. [Unless NC has also amended this section?]

People have previously posted here that in some jurisdictions it is regional practice to ignore this NEC violation, perhaps your location is one of those. Otherwise you may have an issue.

Cheers, Wayne
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
If the job is in NC, then I recall reading here that NC has an amendment that allows up to 6' of outdoor conduit with NM in it, in which case the above is fine. In the unamended NEC, the above would be a violation, because 300.9 says the interior of the exterior conduit is a wet location, so NM cable is not allowed.


Unless the conduit meets all the requirements of 312.5(C) Exception, the cables would still need securing to the cabinet, and stapling them just outside the sleeve is not sufficient. And the installation described does not meet all the requirements of 312.5(C) Exception. [Unless NC has also amended this section?]

People have previously posted here that in some jurisdictions it is regional practice to ignore this NEC violation, perhaps your location is one of those. Otherwise you may have an issue.

Cheers, Wayne

Obviously my post must have been invisible to you....hahahaha
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
I believe it's all NM-B. And yes, the conduit comes out of the crawlspace (to the outside) thru an LB (not a simple elbow as I said in OP) and up a few inches into the outdoor-rated main breaker panel. There is no NM-B exposed to the outside. Sounds the amendment that Dennis quoted above (post #9) covers me there.

Re. 312.5(C), the Romex is all stapled to wood framing in the crawlspace shortly before entering the conduit; it is not secured in any way as it leaves the conduit inside the panel.

Another issue is conduit fill: since NM doesn't appear in the tables, I believe you have to calculate based on cross-sectional area. However, is it not true that short runs of conduit used for "protection" are not subject to conduit fill limits ?

BTW, replacement is because it's a Federal Pacific panel, but that's a whole 'nother discussion ...
I think you have more issue besides the NM outside, even if NC allows it. 312.5(C)(2) is not met from what your statement above appears to say as conductors are coming in from the bottom of the panel.
 

RustyShackleford

Senior Member
Location
NC
Yeah, it would appear I don't meet 312.5(C)(2) exception, because the branch-circuit cables enter from the bottom. This being a straight replacement, maybe it doesn't matter - for example, not required to add AFCI breakers. Yes, this is North Carolina.
 

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
Just build or have someone build a small removable box that matches siding to conceal wires and keep out of wet location . Sell it as easy access down the road.
Or big splice box and transitions to thwn
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Just build or have someone build a small removable box that matches siding to conceal wires and keep out of wet location .
That's not an issue for the OP, as the work is in NC and they have an amendment allowing the NM outside in conduit for up to 6'. The only issue is 312.5(C).

Cheers, Wayne
 

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
well correct on not needing nmb out of wet location.
Second option of transitioning to thwn would still solve his problem with312.5 c
If your allowed 6’ just get ride of lb and pipe and staple to wall and install Uf connectors. Still would need something like first mentioned to protect cable I would assume.
 

RustyShackleford

Senior Member
Location
NC
Seems bass-ackwards to add a whole new set of connections - one per every conductor, including EGCs - just to get around 312.5(c). I'm going to see if it can be grandfathered-in, this being a straight replacement.
 
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