Concern About Junction Box to EMT Support

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msimms

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I have an installation that I question involving metal junction boxes being installed above an eventual drop ceiling, with some that are currently secured to cantilevers which we don't typically approve.

I'm not certain if this is the only NEC reference, but based on how I interpret 314.23(B) regarding structural mounting, I don't believe that the current installation has the box properly supported using this installation. Since its not supported directly off the structural member, I would at a minimum expect a continuous metal support between beams to secure the box(es). Refer to the attached photo.

The installation includes EMT conduit, but 358.30 doesn't exclude installation of boxes in between structural members; only that they're securely fastened following the required intervals. The structural members are currently designed at a center to center spacing of just under 7 ft. I've referenced 2014 NEC Handbook related to this inquiry.

Would appreciate input on this interpretation.

Junction Box Support Concerns.JPG
 
It's mounted to strut, which is mounted to the I beams. The NEC has nothing to say about that. This is a very common installation practice.
 
I would be thrilled if the electricians in my inspection area did that well. :D
 
Cow said:
It's mounted to strut, which is mounted to the I beams. The NEC has nothing to say about that. This is a very common installation practice.
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I agree and it's better than much of the stuff I see on a daily basis.
 
It does seem like a single piece of strut spanning between the ibeams would have been more effective. But it doesn't look like the box would fall down without that EMT coming from the left, so I agree it seems to be NEC compliant.
 
I guess having the strut installed in a cantilever manner was what concerned me, and not so much that about the box being secured to the uni-stut itself. Hence my inquiry about needing a continuous metal support between structural beams. Consider myself properly enlightened. Thanks.
 
msimms said:
I guess having the strut installed in a cantilever manner was what concerned me, and not so much that about the box being secured to the uni-stut itself. Hence my inquiry about needing a continuous metal support between structural beams. Consider myself properly enlightened. Thanks.
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I can think of many applications where support is acceptable and far less secure. I kind of wonder what it was about cantilever that bothered you. We can and do hang a piece of 1/4" rod from a concrete anchor or beam clamp with a box in the end of it. That is an accepted trade practice. How about a run of conduit and fixtures on an exterior overhang, the ENTIRE overhang is a cantilever. Depending on how far away from the beam, I would probably be willing to hang my fat butt off ot it.
 
msimms said:
I have an installation that I question involving metal junction boxes being installed above an eventual drop ceiling, with some that are currently secured to cantilevers which we don't typically approve.

I'm not certain if this is the only NEC reference, but based on how I interpret 314.23(B) regarding structural mounting, I don't believe that the current installation has the box properly supported using this installation. Since its not supported directly off the structural member, I would at a minimum expect a continuous metal support between beams to secure the box(es). Refer to the attached photo.

The installation includes EMT conduit, but 358.30 doesn't exclude installation of boxes in between structural members; only that they're securely fastened following the required intervals. The structural members are currently designed at a center to center spacing of just under 7 ft. I've referenced 2014 NEC Handbook related to this inquiry.

Would appreciate input on this interpretation.

View attachment 19956
Click to expand...

If you assume standard strut of 1-5/8" (Unistrut P1000) and a length of 4 feet, the max allowable load at the end of the strut is 102 lbm and there will be a deflection of 0.704 inches. Unless you're coiling up Osmium wire in the JB I think you're going to be OK.
 
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