Mounting Coduit Boxes

hookoodookuJanuary 25, 2010

Does electrical code require that coduit junction boxes be mechanically connected to the structure? Or would chemical connections (epoxy) be allowed.

I have a 4x4 steel support column that I want to put a switch on. The easiest (and still relible) method I can think of is use conduit, and attach the box to the column with J-B Weld. The weld is STRONG, heat resistant (600 degrees) and doesn't conduct electricity. So I believe the instillation will be safe and durable. But if code REQUIRES mechanical connections, then I can't expect it to pass inspection.

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Excellent question!... wish I knew the answer. I see no mention of it in Ray Mullin's classic 'Electrical Wiring, Residential', or anywhere else, so I agree with you, i.e. assume it's NOT allowed. OTOH it costs nothing (but a little time and aggravation) to call your AHJ. Try using the term "chemical anchor" vs. "epoxy"... sounds better, lol.

I understand your reluctance to drill into a structural steel column, esp. if there's environmental exposure (rust). And welding on a backing plate is a bit over the top.

Will the entire perimeter of column be visible, as in an industrial setting or unfinished basement? Maybe there's a hose-clamp type solution? Perhaps your "loophole" around the code/AHJ is to epoxy your wood/metal/PVC "backer" to the column, and then screw into that... if you can live with the extra standoff. Totally speculating here.

In non-electrical apps, I've used chemically related anchoring epoxies (Simpson Strong-Tie ET/SET, PC-Concrete, etc.), and been very impressed with their strength, but they all have "deflection" temps only in the 150degF range, i.e. the point they start losing significant strength.

That's amazing that JB has a product (which one?) that's good up to 600F!! Need to keep some on hand for radiator leaks. That represents quite an advance in civilian copolymers.

PS: How are you planning on "strapping" the conduit to this column?

Please follow up and let us know how you made out.

    Bookmark   January 28, 2010 at 11:59PM
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I've done the same in my basement shop. The box is held to the pole with epoxy. The conduit was formed with a bender to clear the beam & is secured to the joist above. The box is about 40" off the floor, so no need to strap the conduit to the pole. I don't know if it's to code or not, but I did it 10+ years ago & it's holding up fine.


    Bookmark   January 29, 2010 at 11:11AM
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I've seen JBs not attached to anything except the conduit (commercial applications). Perhaps as long as the conduit is properly secured every (X) feet, a rigidly attached JB is not required to be anchored down.

    Bookmark   January 29, 2010 at 12:36PM
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There is nothing that would prohibit an adhesive from being used to mount a box as long as it is secure after installation.

Boxes can be supported only by the conduit, but only under several specific guidelines.

    Bookmark   January 29, 2010 at 12:58PM
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You should use a mechanical connection. In that situation I would drill and tap the column. Strap your conduit within 3' of the box. I like to do it 18" from the box.

    Bookmark   February 1, 2010 at 7:09PM
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Boxes can be supported only by the conduit, but only under several specific guidelines.

Would one of those guidelines be EMT is not approved/sturdy enough, but IMC and RIGID are? Seems to approx. match what I see... in the world.

    Bookmark   February 2, 2010 at 11:59PM
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