Strain relief for thhn in conduit

[Premium08]

Have a job with conduit running up a ladder and specs are calling for sch 80 PVC and junction boxes. Each junction box is supposed to have strain relief for the thhn conductors. Only strain relief I have used is the Chinese finger type for cable. Has anyone used something that fits inside conduit or junction boxes?

Thanks

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[Eriehunter]

Yes they make a chinese finger style that goes inside conduit, it would rest on the bushing in the bottom of your junction box. The one I used was in 4" EMT, we used good heavy bushings, I believe the conductor size was 4-600mcm copper.

 

[Premium08]

Yes they make a chinese finger style that goes inside conduit, it would rest on the bushing in the bottom of your junction box. The one I used was in 4" EMT, we used good heavy bushings, I believe the conductor size was 4-600mcm copper.

This is only a 20 amp 120v circuit. Will probably use 10awg.

Thanks

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[matt_i]

It seems like a hack at first but the thought came to mind of tying a (loose) knot in the group of conductors as they enter the box. That gives the connections strain relief (especially on vertical runs) but no damage the wires with PVC conduits. The finger trap has to "bite" the surface somehow for it not to slip....granted its small but its there unless you build up a series of tape wraps first.

 

[justsam]

The only junction box strain relief I am familiar with is for cordage, not THHN. Not sure what would be an "approved method" but using some tyraps, or perhaps some form of cable clamp would work.

 

[Bad Habit]

How about something like this...

https://www.heyco.com/Liquid_Tight_Cordgrips/pdf/Multi-Hole-Cordgrips-3.pdf

 

[Premium08]

It seems like a hack at first but the thought came to mind of tying a (loose) knot in the group of conductors as they enter the box. That gives the connections strain relief (especially on vertical runs) but no damage the wires with PVC conduits. The finger trap has to "bite" the surface somehow for it not to slip....granted its small but its there unless you build up a series of tape wraps first.

The box at the end of the run will be the only one with connections. Other boxes will just be pull boxes.

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[Bert_]

For small stuff like the #10 your dealing with I've done the "tie a knot" method. It has always been less than or right around a 100' vertical run, no problems. Bigger wires require something more sophisticated.

 

[Premium08]

For small stuff like the #10 your dealing with I've done the "tie a knot" method. It has always been less than or right around a 100' vertical run, no problems. Bigger wires require something more sophisticated.

Engineer is specifically calling for a strain relief device in the drawings. Spoke with the local electrical supply house and they say they have seen a couple different things. Need to go in sometime and see what they got. He mentioned a cone device that would slide in the conduit and act as a wedge or maybe a kellium grip screwed to the box.

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[LXCam]

They make foam inserts in various configurations for vertical runs that slip into the conduit and then compresses with a external ring deal. I can't remember the manufacturer, it's been a few years since I've boughten any. But check Peco electric, they make this kind of stuff. Also if you get in a pickle I'd suggest you swap out the multi conductor cable and go with a standard issue external sheath strain relief, that's how a lot of elevator controls are done.

 

[alfredeneuman]

. He mentioned a cone device that would slide in the conduit and act as a wedge

AFAIK, those aren't produced in conduit sizes smaller than 1-1/2"

 

[grounded-b]

Use a Kellums grip (Chinese finger lock).

Fasten the grip to the box with a U bolt.

Or use a Kellums grip which has a NPT threaded connector. Use a rigid coupling to join this Kellums grip to the top conduit connector's threads (upside down and back to back )

This last idea must be done prior to pulling conductors

 

[matt_i]

Engineer is specifically calling for a strain relief device in the drawings.

Contact engineer directly to see specifically what he or she had in mind?

 

[teamextreme]

Contact engineer directly to see specifically what he or she had in mind?

That's what I do when I can't find what they want. I know I've seen a product like you're describing, but I don't know the technical name and I had no luck googling. They're used in long vertical runs of conduit; skyscrapers, elevators, etc.

 

[Premium08]

Appreciate all the input guys!

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[Aceman]

If you can't find something easy enough, send an RFI to the engineer requesting the part number of what they're specifying.

 

[Stevie-Ray]

Use a Kellums grip (Chinese finger lock).

Horsecocks!