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How Not To Terminate A Strain Relief Fitting! #104652 10/02/03 05:30 PM
Joined: Oct 2000
Posts: 2,749
Joe Tedesco Offline OP
[Linked Image]

This disconnect is used to supply a large trash compactor in an alley where public access is possible between a hotel and a market!

Joe Tedesco, NEC Consultant
2017 / 2014 NEC & Related Books and Study Guides
Re: How Not To Terminate A Strain Relief Fitting! #104653 10/02/03 07:43 PM
Joined: Aug 2001
Posts: 7,520
pauluk Offline
The cover is nicely padlocked. What a pity somebody didn't apply the same zeal to the rest of the unit. I hope the panel is securely grounded for when one of conductors finally contacts the metal when the insulation wears through.

Unsecured cables, missing or damaged protective seals or grommets, improperly tightened glands etc. seem to be a worldwide problem.

Re: How Not To Terminate A Strain Relief Fitting! #104654 10/02/03 08:08 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
This is a good image showing that concentric knockouts and flexible raceways or cables should not be considered a compatible arrangement... Sheet-metal reducing washers are also very marginal/of potentially unacceptably high impedance for equipment-grounding integrity to the metallic connector. In my book, suitably-threaded reducing bushings and a pair of locknuts are far more desirable.

Re: How Not To Terminate A Strain Relief Fitting! #104655 10/02/03 08:27 PM
Joined: Apr 2002
Posts: 7,218
HotLine1 Offline
OK, I have to type this.....
As it appears the cord is aiming "down", along with that gravity thing.....why wouldn't you exit the disc at the bottom??

Is this outside? that doesn't look like a suitable strain relief.


Re: How Not To Terminate A Strain Relief Fitting! #104656 10/02/03 10:48 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
The pictured cord connector is a kellems-type grip. That should be a good application sans the KO donuts.

[Linked Image from]

[This message has been edited by Bjarney (edited 10-03-2003).]

Re: How Not To Terminate A Strain Relief Fitting! #104657 10/03/03 05:03 AM
Joined: Jan 2003
Posts: 4,391
iwire Offline
My personal feeling is that equipment should not come with concentric knockouts.

The company I work for orders all panel tubs, troughs and cans with no knock outs.

If your an electrician you should have the tools to make the holes the right size and where you need them.

This picture is a perfect example of why, if I was forced to use for this rubber cord I would install reducing washers over the entire concentric KO.

Now why is there rubber cord hanging from this disconnect anyway. 400.8(1)

Bob Badger
Construction & Maintenance Electrician
Re: How Not To Terminate A Strain Relief Fitting! #104658 10/03/03 08:39 AM
Joined: Nov 2001
Posts: 745
mamills Offline
Hi Guys: I have a couple of questions about this. Since using the concentric KO's for this type of application is obviously not suitable, and if for some reason it is not possible (or desirable...?) to exit from the bottom of the enclosure, Would there be anything wrong with using a KO punch to set one properly sized hole above the concentric?

Is a kellems grip suitable for use outdoors like this - I'm assuming this is an outdoor install bacause of the 3R disco?

Mike (mamills)

Re: How Not To Terminate A Strain Relief Fitting! #104659 10/04/03 07:13 AM
Joined: Oct 2002
Posts: 482
Zapped Offline
I'm assuming the rubber cable (SO, as we call it here) can be explained as the supply cable that came with the equipment (the trash compactor). I've seen these type of hook-ups on some very large compactor units installed behind huge movie houses in California, Idaho, and Texas. I've always assumed this installation was acceptable only because these compactor units were installed in their own masonry-block enclosures (they all passed inspection).
If, however, this particular installation is within a public traffic area, I would certainly think protective conduit would be required.

Also, even if this connector were installed properly, what about water intrusion? This is a wet location, is it not?

Re: How Not To Terminate A Strain Relief Fitting! #104660 10/04/03 02:02 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
mamills — The pictured style of mesh/basket grip may only be rated dusttight and not rain- or watertight. See page 67 of:

BTW—equipment manufacturers hate concentric KOs for a different reason—their punches and dies to stamp that pattern in sheet metal are a constant headache in terms of maintenance—they are hard to keep sharp. I agree than “NOKO” cans and wireways make for a much neater installation, and generally improve raceway grounding continuity. Some consider installation of offset nipples or connectors “tacky,” and not the mark of a true electrician.

The matter of KO location in 3R disconnect switches/enclosures is a salient one. As I see it,
99NEC430-91 Motor Controller Enclosure Types discuses the issue, but article 430 only indirectly covers disconnect switches and not “pull cans” containing circuit conductors which may be exposed/live with the cover removed, or insulated to a “600-volt” degree. I have an impression of what should be addressed, but cannot provide a specific reference in a ‘code-like’ publication or standard. There are bits and pieces on “Enclosure Types” at places like:

In case of the pictured disconnect, you could interpret that factory-provided KOs are permitted when any part of their opening is below exposed energized parts within the enclosure. Any opening that encroaches on live parts would generally require the equivalent of a gasketed hub, if I interpret that correctly. Yes or no?

Re: How Not To Terminate A Strain Relief Fitting! #104661 10/04/03 02:34 PM
Joined: Jan 2003
Posts: 4,391
iwire Offline
Zapped if we go with the assumption that this feeds a trash compactor pump (or any equipment) and you want to use a flexible cord ,the closest article that would allow this would be 400.7(A)(6), but in order to be able to say it is for frequent interchange it needs to have an outlet and plug.

If you have to unwire the cord to change the equipment you could just as easily unwire a piece of LFMC.

400.7 Uses Permitted.
(A) Uses. Flexible cords and cables shall be used only for the following:

(6) Connection of utilization equipment to facilitate frequent interchange

But with the cord hardwired into the disconnect IMO it is a violation of 400.8(1) and (4)

400.8 Uses Not Permitted.
Unless specifically permitted in 400.7, flexible cords and cables shall not be used for the following:
(1) As a substitute for the fixed wiring of a structure

(4)Where attached to building surfaces


I have no doubt that concentric knockouts are a headache for the manufactures, set the dies to tight and the KOs will fall out, let them get to loose and the KOs are no more than an outline of the KOs that are not removable with a sledge hammer.

I think a big problem with premade KOs is that they often end up half way in the way, so when you punch a hole where you want you end up with a hole resembling an 8. [Linked Image]


[This message has been edited by iwire (edited 10-04-2003).]

Bob Badger
Construction & Maintenance Electrician
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