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Old 10-24-2018, 08:41 AM   #1
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Getting #6 wire to surface mount conduit


I'm trying to figure out how to legally get #6 wire from my flush mount electrical panel into surface mount conduit. My intent has been to bring it into a surface mount junction box from behind. The ideas I've come up with and why I don't think they're legal are as follows:

1) Use Romex/NM with the appropriate clamp.
The minimum been radius is 5 times the diameter which for the 6/3 wire I've found works out to about 4.5 inches; this too much for my 2x4 walls.
2) Use conduit (rigid / EMT / FMC / LFMC / LFNC / etc.) the same bend radius problem as NM only worse. Also there are 90 fittings but, from my reading, those need to be accessible when used with conduit so couldn't be used on the back of a box.

Now I can think of a couple ways that may be legal but I don't like.
1) Use MC. I believe it is legal to take MC to a 90 deg box fitting and have it inaccessible behind the wall. However, unlike NM I can't find it by the foot so would end up buying 25 or 100 feet when I only need 5 feet.
2) Run NM to a flush mount box and then use a 90 elbow out through a drilled blank faceplate. This just seems like a hacky / ugly solution. Especially because I'll still need to go to a junction box for my application.

Any other ideas or am I wrong in my understanding of the rules?

Thanks.
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Old 10-24-2018, 10:36 AM   #2
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Re: Getting #6 wire to surface mount conduit


Run NM into the back of a 4" square surface mounted box. Start conduit from box.

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Old 10-24-2018, 03:14 PM   #3
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Re: Getting #6 wire to surface mount conduit


Use flexible conduit (keep it short) from panel to a surface mount box to start the conduit (EMT) run.
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Old 10-24-2018, 04:29 PM   #4
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Re: Getting #6 wire to surface mount conduit


Assume your trying to come out the back of the panel because studs are
in the way on the sides. Correct?
If so can you come out top or bottom instead?
How about hole sawing through stud to access knockouts?
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Old 10-24-2018, 05:08 PM   #5
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Re: Getting #6 wire to surface mount conduit


Why are you attempting this with romex ?
If this is a complete conduit system, why not individual conductors (such as THHN) which have a smaller bending radius than the cable assembly ?
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Old 10-24-2018, 11:36 PM   #6
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Re: Getting #6 wire to surface mount conduit


Maybe I wasn't clear in my original message. I am trying to run three #6 conductors (plus ground) out the bottom of a flush mounted breaker panel into the back of a surface mounted junction box which will be about 12-18 inches below the breaker panel. The walls are 2x4 construction so I estimate I have about 3 1/2 inches (best case) for the allowable bend radius of the conductors / conduit / etc. (depending on how the minimum bend radius is measured).

The ideas I've had for how to do this and the problems I see with them are as follows:

1) Use a "rigid" conduit (whether that is rigid, EMT, or PVC) and THHN. Based on the number of conductors I would need 3/4 inch which, I've found sources that give a minimum bend radius of 4 1/2 inches for EMT and larger for other materials. This is too large to fit in the wall cavity.

2) Use flexible conduit such as FMC. Once again requires 3/4 inch diameter and I run into the same problem if I need to bend it to be perpendicular to the back plane of the junction box to use a straight connector into the junction box. I've found references that state a minimum bend radius of FMC to be 4 inches and 4 1/4 inches for LFMC. These are still too big of a radius for an area with only 3 1/2 of room. There are 90 degree connectors that in theory would work but based on what I've read I believe those are not legal to be used with conduit in an enclosed area per NEC 348.42 (such as within a wall). I fully admit I may be misunderstanding this restriction and this type of junction box application may be completely legal. In fact I'd be happy to be wrong because that would be an easy solution to my problem.

3) Use Romex. Here it looks like I may have had some bad information originally. My understanding is the minimum bend radius is 5 times the cable diameter. When I did my initial search I found a cable diameter of just over .8 inches for 6/3 which gives 4+ inches for the bend radius. Since my original post I've found other manufacturers quote an outer diameter for 6/3 of about .6 inches which puts me around 3 inches minimum bend radius and thus in theory would be adequate to come into the back of the box as I intended.

Thanks for all the input.
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Old 10-25-2018, 07:00 AM   #7
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Re: Getting #6 wire to surface mount conduit


Any reason the JB can't be partially recessed? If so recess it enough to allow
a straight conduit from the bottom of the panel to the top of the JB. Front of
the JB can still jut out if you wish. This would allow you to run other conduits
on surface from the JB. No idea what your bigger plans are but this would
also allow for the JB to be used as a pull box with no junctions.
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Old 10-25-2018, 08:27 AM   #8
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Re: Getting #6 wire to surface mount conduit


Does it half to be a surface mounted box?
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Old 10-26-2018, 03:55 PM   #9
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Re: Getting #6 wire to surface mount conduit


Quote:
Originally Posted by VestigialSoul View Post
2) Use flexible conduit such as FMC. Once again requires 3/4 inch diameter and I run into the same problem if I need to bend it to be perpendicular to the back plane of the junction box to use a straight connector into the junction box.
Use a box and extension ring to eliminate the need for the 90 degree connector. The box mounts flush in the wall and the ring mounts at the surface. If you can manage to get the FMC to a single gang box there are adapter rings which do a nice job of hiding the gap at the drywall.



If you need to cut a larger drywall section to gain access, there are also gasketed flanges available to install between 4"x4" boxes and extension rings. These look a little more industrial but still hide the gap around the box.

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Old 10-26-2018, 05:49 PM   #10
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Re: Getting #6 wire to surface mount conduit


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Use 90 degree FMC fittings at start and end then flex conduit just does gentle sweep in wall cavity.


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