Transitioning Wire from Interior 2x4 wall Through Back of Exterior Surface Mounted Panel

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
I may consider the unnecessary addition of transitioning to TWHN in the J-Box to avoid rejection.
No need for that, that adds a unnecessary splice and box fill.
The only time I have seen an inspector reject a cable in a (interior) raceway is when it was some BX cable in a pipe, then a gutter (not done by me of course).

I think @Dennis Alwon is the only one I know of that has had a PI accepted in part for 312.5(C) in the last 30 odd years.
So would be good to get his eyes on a PI and make a new thread for it.
And even if you submit a PI and it gets rejected the CMP's published statements/remarks are 'admissible evidence' when dealing with AHJ.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
One thing I also see super often around here is a 2" LB below the panel to the crawlspace, then a big (e.g 10×10×4) box in the crawl. Little bit annoying to pull things through an LB but better than opening the walls.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Exterior panels have been popular here for upgrades in older houses for decades. They have either cable clamps in the back of the panel or conduit and LBs into the crawl space.

Many of them have multiple smaller conduits as new circuits were added over time.

When I have done this (it's been a while), I usually used two 2" pipes and LBs, but no box. Just stapled the cables near the mouth of the conduit.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
One thing I also see super often around here is a 2" LB below the panel to the crawlspace, then a big (e.g 10×10×4) box in the crawl. Little bit annoying to pull things through an LB but better than opening the walls.
Exterior panels have been popular here for upgrades in older houses for decades. They have either cable clamps in the back of the panel or conduit and LBs into the crawl space.

Many of them have multiple smaller conduits as new circuits were added over time.

When I have done this (it's been a while), I usually used two 2" pipes and LBs, but no box. Just stapled the cables near the mouth of the conduit.

Yeah thats what I was talking about in post 44, I have had to argue with an inspector that the 2" LB is a junction point, between a '300.18 Exception' protective sleeve (short PVC nipple from LB to crawlspace) and a complete raceway (section form lb to bottom of panel).
 

letgomywago

Senior Member
Location
Washington state
Occupation
residential electrician
Yeah thats what I was talking about in post 44, I have had to argue with an inspector that the 2" LB is a junction point, between a '300.18 Exception' protective sleeve (short PVC nipple from LB to crawlspace) and a complete raceway (section form lb to bottom of panel).
I've done that install before too but no one has ever argued it. I try to avoid it though because I feel it's not as future proof as other options but sometimes you don't have any others.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
No need for that, that adds a unnecessary splice and box fill.
The only time I have seen an inspector reject a cable in a (interior) raceway is when it was some BX cable in a pipe, then a gutter (not done by me of course).

I think @Dennis Alwon is the only one I know of that has had a PI accepted in part for 312.5(C) in the last 30 odd years.
So would be good to get his eyes on a PI and make a new thread for it.
And even if you submit a PI and it gets rejected the CMP's published statements/remarks are 'admissible evidence' when dealing with AHJ.


I don't think so. I did write a proposal way back for that section but it was rejected. I believe I was trying to get the cmp to allow a conduit going down as it only allows the conduit to be install at the top. So much was going on in my life that I can't remember if I wrote it or thought about writing it. lol
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I presume the reason that 18" up is okay but any other direction is not is that gravity is presumed to sufficiently counteract upward movement of hot metal from arc flash out of the enclosure.

Still curious why duct seal wouldn't be sufficient for under 250V.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
I don't think so. I did write a proposal way back for that section but it was rejected. I believe I was trying to get the cmp to allow a conduit going down as it only allows the conduit to be install at the top. So much was going on in my life that I can't remember if I wrote it or thought about writing it. lol
You added what is now item (7) then (g) my friend.
Submitter: Dennis Alwon, Alwon Electric Inc.
Recommendation: Revise text to read as follows:
(g) Where installed as conduit or tubing, the allowable cable fill does not
exceed that permitted for complete conduit or tubing systems by Table 1 of
Chapter 9 of this Code and all applicable notes thereto except Note 2.
Substantiation: As written, this exception makes no sense since it takes us to
Table 1 of Chapter 9 Note 2 which states that for sleeves Table 1 is not
applicable. Section 312.5(C) is about sleeving NM cables into a panel. So we
are told to use Table 1 then we are given exemption from using Table 1. If the
intent is to consider conduit fill then Note 2 should be excluded otherwise the
entire section (g) should be excluded.

I was remembering this thread:
https://forums.mikeholt.com/threads/312-5-c-exception.2553289
Hartwell the head of CMP-9 agreed with you, that's where the quote comes from, I think they re-worded it slightly and approved it.
HARTWELL, F.: This proposal should have been accepted. In spite of this
being one of the most surprisingly controversial, passionately debated, and
exhaustively studied topics in the history of CMP 9
, there is a problem with the
wording that the proposal corrects. This exception has a long, tortured history,
and unfortunately only two members of the panel present for the discussion of
this exception (Hartwell and Sengupta) in the 1993, 1996 and 1999 cycles
remain at this time, and the lack of that shared experience influenced the final
panel action. This exception began with Proposal 9-69 in the 1993 cycle
followed by 19 public comments, which resulted in a special task group being
created to produce acceptable text for the 1996 cycle. The task group (chaired
by this member) gave the issue exhaustive study, including the 21 proposals for
the 1996 NEC submitted by the public on the topic, and reported what became
Proposal 9-66a from the panel. This was followed by 10 public comments,
which resulted in the proposal remaining accepted by show of hands on a vote
of 11 to 2 at the meeting. However two votes changed during recirculation, one
by facsimile with only 30 seconds remaining. The final vote of 7-4 was one
short of the required two-thirds, and so we moved on to the 1999 cycle, Finally
after merely two proposals and six public comments (bringing the total number
of panel actions on this topic to 60) the final language entered the NEC at last.
The record shows that CMP 9 was properly concerned with the integrity of
large numbers of cable assemblies pulled into a common sleeve, along with
mutual conductor heating. This is why the informational note says what it says,
and why paragraph “(g)” is included. At the meeting the current CMP 9 chair, a
veteran of CMP 8, correctly pointed out that a sleeve that is purely for
mechanical protection for one or two cables can be filled without regard for
raceway fill. This application is somewhat different. This is a method of
bringing large numbers of cables into a cabinet through a common raceway,
generally for aesthetic purposes. It has been done for generations in numerous
jurisdictions. If the raceway is short enough to qualify as a nipple, then mutual
conductor heating derating penalties do not apply. This is the customary case,
as in an instance where a panelboard is surface mounted below a suspended
ceiling in a commercial occupancy. CMP 9 imposed the 18-inch minimum
length to assure that a fault in the cabinet would be contained
, along with many
other provisos to cobble together the required panel majority, each one fought
out during protracted discussion. We overlooked, however (and no member of
the public raised the question until this cycle) that Note 2 could be
misinterpreted to countermand the intended application of the factors covered
in the informational note. The panel statement does not respond to the merits of
the proposal, which should be accepted in some form.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Ah yes, I remember but it wasn't accepted.

Reading that now I had to remind myself and look at the 2008 code to see what was going on.... I remember Hartwell supporting my proposal on the surface but it needed some re-write, I didn't realize that they accepted it in the following cycle. I never looked or took note of it. hahaha

Thank you for reminding me of this. I truly forgot about it.
 

tom baker

First Chief Moderator
Staff member
This is how I went from inside to outside. Existing house, panel outside install by previous owner. If I was doing the panel would of gone inside, but previous owner was a DIYer. Note how hot and neutrals are grouped, and the ground bus in the back of the ww. Seems like all the other methods mentioned take a lot of fussing with zip ties, and other odd methods 1674680407055.png
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
This is how I went from inside to outside. Existing house, panel outside install by previous owner. If I was doing the panel would of gone inside, but previous owner was a DIYer. Note how hot and neutrals are grouped, and the ground bus in the back of the ww. Seems like all the other methods mentioned take a lot of fussing with zip ties, and other odd methods View attachment 2563743


Sure that works but so expensive and.....Technically you cannot strip the nm cable inside the nipple..... Ridiculous

The whole routine makes it difficult with exterior panels especially
 

ESolar

Senior Member
Why can't duct seal be used to deal with the arc flash concern for under 250V? That's not its intended use? Has any testing been done?

As far as a strictly code compliant install under the current rules, this kind of thing is a good option. You can get blank 5-gang wall plates.

https://www.gordonelectricsupply.com/p/Garvin-Tb-535-3-1-2D-5G-Masonry-Box/6252471

As a battery backup guy, I actually very much appreciate it if stuff is brought into a box behind the panel instead of the panel itself. Makes it easier for me to install a partial home backup panel with a separate nipple to the box, and then move the loads around at the customer's pleasure.
That volume box would actually work for clamping and passing the cable through. The question is will the inspector complain about pass cable into the box.
 

SSDriver

Senior Member
Location
California
Occupation
Electrician
Show me a NEMA3 flush mounted subpanel and I'm game.
The rule would be great with semi-flush meter main combos we use here(CA) all the time and NEMA 1 indoor subpanels as well. I would love to see a manufacturer make a flush or semi flush 3r sub-panel. I don't understand the reasoning for 312.5c not being allowed on flush panels.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
I don't understand the reasoning for 312.5c not being allowed on flush panels.
Just talking about the Exception,
In 2005 and 2020 a proposal to delete “surface mounted” was rejected
9-7 Log #3446 NEC-P09
(312-5)
Final Action: Reject

Recommendation:
Exception: delete surface mounted.
Substantiation:
It is easy to add conduits (circuits) to surface mounted panels/cabinets. It can be very difficult to add circuits to flush mounted panels/cabinets. If the panel is flush mounted and the wall is an outside wall, or near an outside wall, holes cannot be drilled in the top of the wall, wires cannot be fished to the panel, therefore the finished wall must be unnecessarily removed and refinished (at additional unnecessary cost) just to add one circuit. And again later to add another circuit each time a new circuit is needed.


Panel Statement:
Permission for use with other than surface mounted enclosures will confuse the issue of penetrating a structural ceiling. Most flush mounted applications would involve penetration of building structural members if the exception were to be utilized.
Number Eligible to Vote: 11
Ballot Results: Affirmative: 11

The 2020 proposal Public Input No. 2812-NFPA 70-2017 [ Section No. 312.5(C) ]
Was similar and the panel statement was:

Committee Statement
Resolution:
This exception was developed during the 1993 and 1996 code cycles and first appeared in the 1999 NEC. During the development and after it was published, this exception has been the subject of many proposals and comments.
  • The reason for the surface mounted condition is that there is no need for the use of the sleeve in a flush mounted application as the conductors are protected from damage by the wall covering.
  • The limitation of entering the “top of a surface mounted enclosure” was to assure that the outer raceway termination won’t be easily accessible.
  • The substantiation for Condition #2 is to prevent the spread of fire or products of combustion and to ensure that the fitting remains accessible after the installation.
CMP 9 continues to support the substantiation for the exception and determines the current requirements are correct.
 

ESolar

Senior Member
The rule would be great with semi-flush meter main combos we use here(CA) all the time and NEMA 1 indoor subpanels as well. I would love to see a manufacturer make a flush or semi flush 3r sub-panel. I don't understand the reasoning for 312.5c not being allowed on flush panels.
If you read this entire thread, you find that the intent of the code is to contain an arc blast (I was not aware of that - I assumed it had to do with water entry). The arc blast concern would also apply to a flush mounted panel. In my own home, an interior flush mount panel was installed with all of NM stuffed through one big knock out in the top - no clamps and no duct seal. Doesn't this present the same problem that the code was trying to prevent with 312?
 

ESolar

Senior Member
If you read this entire thread, you find that the intent of the code is to contain an arc blast (I was not aware of that - I assumed it had to do with water entry). The arc blast concern would also apply to a flush mounted panel. In my own home, an interior flush mount panel was installed with all of NM stuffed through one big knock out in the top - no clamps and no duct seal. Doesn't this present the same problem that the code was trying to prevent with 312?
Oh - and when I moved in I noticed that they had the feeder neutrals and grounds switched (connected to opposite bars). I switched them back. The ground is bare.
 
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