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

[tortuga]

In my own home, an interior flush mount panel was installed with all of NM stuffed through one big knock out in the top

Like this?

 

[letgomywago]

It looks like it's easier to get local amendment for any of the reasonable alternative ideas than to dare question anything in this section. I wonder how the code panel thinks New Zealand gets by with the backless boxes and not setting the whole island on fire based on the idea that fire stopping won't be considered in the installation of a conduit sleeve to a panel.

 

[ESolar]

Like this?
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Yes. Is that an issue?

 

[SSDriver]

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?

I'm specifically asking about keeping their c same rule and only making a change that would allow it to be used on Flush mount panels as well as Surface mount. Surface mount is all it allows for on 312.5c

This rule would be to allow us to use a piece of 18" conduit out the top, seal it up, on a surface or flush mount panel(not just surface mount as the code currently reads). I don't see any additional danger than a flush mount panel with cheap plastic push in NM buttons. I would bet the 18" long conduit with NM out the top and sealed would contain an ARC blast better than a panel with 20 NM buttons on the top. The CMP needs to get there heads out of their A$$ and suck up some pride. They make arbitrary rules based on nothing, if we ask to change them they want to see studies done.

 

[SparkyBirdman]

I have been an SME on a NFPA 70E arc flash coordinated study for a relatively large electric utility when they were revising their standards for not only their inside wiremen, but lineworkers, meter techs, substation electricians, building maint, etc. very in depth. They paid for an outside engineering firm, AECOMM (very well know national engineering firm that does alot of utility work), to look at all the transformers, cutouts, ct cabinets, HV breakers, yadayada-and tell us the arc hazard for each. Out of all equipment and voltages (120V through 230kV), a typical 3ph 480V panelboard was the most dangerous. The meter techs were most at risk while working hot. The 120/240/208V they said were almost negligible for most smaller load centers and meter combos-especially on the load side of an mcb. I read through this whole thread and I understand the intent of reducing exposure/damage to arc blast. HOWEVER, that being said, I want to see the data the CMP used in determining that a resi 120/240 meter combo or load center has a potential high enough arc blast that there is a difference from 12 romexes in a 2in nipple or shorter than 18” pvc nipple; compared to 1 or 2 romexes in a plastic nm connector. If you’re telling me that a plastic romex connector offers more arc blast protection then a bunch of romex in a single nipple or 2in 2 screw clamp, Ill turn in my license and join the plumbers. Ive never heard in 20 years of an arc blast in even a 400A resi meter combo, blow through any openings and start a fire-and Ive added circuits to 50 year old 3 phase zinsco panels.

 

[tortuga]

I want to see the data the CMP used in determining that a resi 120/240 meter combo or load center has a potential high enough arc blast that there is a difference from 12 romexes in a 2in nipple or shorter than 18” pvc nipple; compared to 1 or 2 romexes in a plastic nm connector.

From my reading of the failed proposals I think a proposal would have to define how full that 18" nipple has to be, can it be a 3" PVC with one 14/2?
Can it be less than 18"?
Then someone would need to do a study or some testing which would of course need to be paid for, or at least sponsored and have a university engineering dept do it.

Ill turn in my license and join the plumbers.

Now lets not get that extreme

 

[jaggedben]

Why can't duct seal be adequate for under 250V?

 

[SparkyBirdman]

It is all relative, I understand that-I certainly wouldn’t make it a blanket rule for say, a 480 panel or 1000V and higher panels, which doesn’t apply anyway as you aren’t putting NM in those anyway (I hope not anyway). Ive seen the data, talked to the engineers and Im sure we’ve all seen the videos on youtube about arc flash/blast. For a resi 120/240 panel on the load side of the main, I would be VERY surprised if an arc blast is even nearly powerful enough to start an instant fire inside a wall after traveling through any length of nipple. How many of us have had a breaker fall apart and blow in our face or (lets all admit it!) our screwdriver grounds out or touches a hot part and we didnt have our faces melted off like we were in an Indiana Jones movie? On top of the fact, there is quite literally a 100 years of installed systems in homes like this, and I would go out on a limb to say that any fires in that time, were not caused from installing cable this way.

However, the Code has plenty of places that only apply to certain items, so having an exception purely for NM in resi or less than 250V applications for this scenario is not extreme or even out of norm.

 

[garbo]

This has never ever been an issue for me.

And with a strict reading of the code, as long as the nipple does not exceeded 24”, no derating is required.

And while raceways outdoors are considered a wet location, romex has been fed into exterior mounted panels for as long as romex has existed.

The Code is great, but it’s not the Holy Bible.

We were told at an IAEI continuing education class about five years ago that NM cable should never feed into say a pancake box for a wall mounted luminare. Reason given was this is a damp location so NM cable is not approved for damp location. Told us to use UF cable. So appears that you should never run NM cable to outdoor panels.

 

[SparkyBirdman]

Not securing cable to the enclosure is just one of the issues with a rear entry of an exterior, surface mounted panel. It can be done in a satisfactory, if not an entirely code compliant fashion. However of the many hundreds that I have seen it was done satisfactorily fewer than five times.

The typical LA County residential electrician isn't interested in code compliance... mostly because they don't know any code. The cable comes through a big hole or a bunch of little holes. Sometimes there's fittings and sometimes not. The panel enclosure is mounted over a gutted flush panel or just a big hole in the stucco. Quite often there are splices behind the new enclosure. The finishing touch is to caulk around the top and sides of the surface mounted enclosure. Once the sun dries the caulk to a brittle ribbon, water is able to get in the wall.

Having read this thread I see that many of you are okay with a 2" nipple. That could work. The rub is that it takes an extra inspection to see that the wall has been restored and the nipple will be sealed. Did I indicate that it is just one extra inspection...well let me mention the lath inspection prior to stucco and then you provide a picture of the stucco patch.

So in LA County rear entry is not pemitted. I suppose that if you talk to the inspector and arrange the extra inspections, it could happen. But trying to control that with a hundred panel upgrades each day doesn't work. So no, if it comes down to being picky to put a stop what you see in the pictures....so be it.

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In NorCal, I have done around 200 panel changes in 20+ years and I, nor any of the contractors I’ve worked for would have done or allowed work like the pics you’ve shown. I would say looking at those pics, those were not ‘electricians’; those were just ‘installers’-no real knowledge of code or building reqs or best practice. Hopefully, those pics are from inspectors who did their jobs and caught it and made them fix it.
I have done plenty of replacements where we remove the flush mount and install a surface mount. MOST of the time, cables are long enough to go through the back of the new panel with no real issues. Yes, I have used a 2” 2 screw romex clamp and pushed 12 romexes through it. Every electrician I know has done that and no ones house has burned down from it. However, we would always take the old panel out the wall, put a proper backer behind the new, seal the wall, attach new panel, and seal the border with proper outdoor siding (or stucco patch if you have the time and capability). Any wires that were too short, make a hole above or below, mount a jbox either on the surface or in the wall and run a new length of wire to the panel. Hiding a splice in a wall no matter how good you think you are at making them is a NO-NO. NEVER EVER EVER DO THAT.

Point being, a panel change with wire entering the back can be done safely and effectively and still maintain the weather barrier of the house. Just because California passes out journey cards and C10 licenses like candy and these bozos do something wrong, doesnt mean the installation method is bad. Just they dont have any brains