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Discussion Starter · #1 ·
I have a client who is installing some machinery in the middle of his shop. 20' ceilings/steel structure. We're looking at a 3-phase 20A twist lock. I know I've seen SJO type cord in big box stores with strain relief that looks like fingercuffs for pulling big wire in pipe. I've never had to do anything like this before, so I thought I'd put it out there and see what you guys would recommend. Rigid drop?? I'll be piping over to the location overhead and trying to drop down. I hope that explains it well enough.
 

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I've done that exact set up you explained. We would hit a box and use a kellum (strain relief) to hang the cord. You can get a connector with the cord relief right on the end. Worked out awesome, we even did a 100a drop. That was a big cord and the twist lock was immense!
 

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Discussion Starter · #3 ·
I've done that exact set up you explained. We would hit a box and use a kellum (strain relief) to hang the cord. You can get a connector with the cord relief right on the end. Worked out awesome, we even did a 100a drop. That was a big cord and the twist lock was immense!
A google search for "Kellum strain relief" yielded perfect results. I hope my supply house has these on hand. So it looks like you just pop out of the side of a box with the kellum connector and SJO and drop down to the service location with a female twist lock. Great info. Thank you.
 

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We faced the box up and came out the bottom knockouts. Or face down with a blank and a knockout.

If it was really critical I mounted strut and shot a laser to get the box perfect.
 

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Where is the strain relief located on the cord, near the top or do you slide it down the cord closer to the receptacle?

How far can an SO cord support itself (in the vertical) before needing additional support? I don't know although I'm pretty sure there is one.
 

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hardworkingstiff said:
Where is the strain relief located on the cord, near the top or do you slide it down the cord closer to the receptacle?

How far can an SO cord support itself (in the vertical) before needing additional support? I don't know although I'm pretty sure there is one.
It depends on the kellum. We used some that were right at the box, where others can be a little lower you just have to attach the relief to structure.

I believe we used a SO cord that was rated for drops and had extra support integral to the cord
 

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They make an attachment with a spring, you loop out of jbox. And leave a few feet and this kellum sits in the middle of cable. For added strain relief. You can add as many of these for support as needed.
 

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I've probably done a million cord drops during my time as a factory electrician. I normally do them like this:

  • Set 4-square or other suitable junction box on bar joists with beam clamps or whatever
  • Come out of the side of the box with the rubber cord, about 1 foot horizontally along the bar joist
  • Make about a 1 foot diameter loop in the rubber cord and zip tie in three opposing spots. (This is the slack for the inevidable move left or right a smidge)
  • Slide cord drop grip over cord.
  • Connect cord drop grip to drawbar spring (picture below)
  • Hang drawbar spring from beam clamp or other suitable fastening device (eye bolt if wood)
  • Terminate plug cap on bottom end of cord at the required height.

 
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If you want to get real fancy, at the plug end you can use a plug cap grip that has two eyelets. You disassemble the clamping part of plug cap and put it between the halves of the plug cap clamp and reassemble. Pretty bulletproof if you think the cord might get jerked on a lot.

 

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I believe we used a SO cord that was rated for drops and had extra support integral to the cord
Yeah, that's the stuff you're really supposed to use. It's called "Bus drop cord". It has heavy plastic filler fibers inside. Some have Kevlar fibers. "Strain members", I think they're called. Some cord that is used for pendant controllers that will get jerked on a lot has a tiny stainless steel wire rope inside, and you're supposed to terminate it around a bolt inside the junction box at the top end, and around a clamping feature inside the pendant controller at the bottom end.
 

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FWIW, if you don't have time to order drawbar springs from Grainger, and you want to use them, you can get them at the hardware store. They sell them for use on storm door wind chains and for use on porch swing chains.
 

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Discussion Starter · #14 ·
MDShunk said:
FWIW, if you don't have time to order drawbar springs from Grainger, and you want to use them, you can get them at the hardware store. They sell them for use on storm door wind chains and for use on porch swing chains.
This is going to work for me. What's your preferred method for attaching the SJO to the drawbar?
 

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Appleton makes one very similar that I occasionally used for cord that got into the very heavy gauges. I'll see if I can drag up a picture someplace.

EDIT:
Does that actually clamp the cord between halves? Or do you just hang the cord through it? Adalet makes bigger ones with heavier springs. We used some for 6/4 SOOW for welder drops.
 
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