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KO Seals #77988 08/06/01 07:32 PM
Joined: Oct 2000
Posts: 2,749
Joe Tedesco Offline OP
[Linked Image from]

Are KO seals required to be of any specific thickness??

Joe Tedesco, NEC Consultant
2017 / 2014 NEC & Related Books and Study Guides
Re: KO Seals #77989 08/06/01 07:55 PM
Joined: Nov 2000
Posts: 2,148
resqcapt19 Offline
I don't believe that the KO shown in this thread meets the requirements of 110-12(a). This section requires that the hole closed provide protection substantialy equivalent to the wall of the equipment.

Re: KO Seals #77990 08/06/01 07:56 PM
Joined: Mar 2001
Posts: 345
tdhorne Offline
Unused Openings.
Unused cable or raceway openings in boxes and conduit bodies shall be effectively closed to afford protection substantially equivalent to that of the wall of the box or conduit body.

The seal you provided the picture of is listed, yes. If you are using something other than a listed blank I would think it would have to be as thick as the wall of the box.

Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
Re: KO Seals #77991 08/07/01 08:27 AM
Joined: Nov 2000
Posts: 2,148
resqcapt19 Offline
Even if it is listed, it doesn't meet the code rule. What gives UL or other NRTLs the right to change the code????

Re: KO Seals #77992 08/07/01 12:32 PM
Joined: Mar 2001
Posts: 2,056
Redsy Offline
I don't know if the plug affords "substantially equivalent" protection any more than I know how many wraps of tape are required around a splice to provide insulation "equivalent to that of the conductor", as required by 110-14(b). I don't have a roll in front of me, but isn't the di-electric strength of Scotch33 in the thousands of volts? Does that mean one layer on a 480 volt splice is sufficient? Or, is puncture resistance the issue? How many layers would this require?
I dunno!
As far as the plug, if the issue is mechanical strength, or to prevent foreign material, I see nothing wrong with the plug shown. If the issue is to contain a fire, it probably provides at least as much protection as most standard panel covers.

Re: KO Seals #77993 08/07/01 01:32 PM
Joined: Nov 2000
Posts: 2,148
resqcapt19 Offline
I don't see how it can provide "substantialy equivelent protection" when it has a thickness of about 1/5 or less of a standard electrical enclosure.

Re: KO Seals #77994 08/07/01 05:31 PM
Are we protecting against insertion of fingers and objects? Hammer and nail? Heat and meltdown? Explosion?

Re: KO Seals #77995 08/07/01 06:16 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
If this KO closer was used on any NEMA 1 enclosure, I would say that it is in compliance.

NEMA's definition of a NEMA 1 enclosure states "Type 1 - Enclosures constructed for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment and to provide a degree of protection against falling dirt."

Since the KO closer in question will provide the same protection as the enclosure, the fact that it is thinner is a non-issue, regardless of the wording of the NEC. As thin as this closer is, i don't think I could poke my finger through it.

I've seen just about everyone on these boards, at one time or another, state that they would accept work that did not meet the letter of the NEC, I think this is one of those areas.

[This message has been edited by Tom (edited 08-07-2001).]

Few things are harder to put up with than the annoyance of a good example.
Re: KO Seals #77996 08/07/01 07:04 PM
Joined: Oct 2000
Posts: 3,961
Bill Addiss Offline

(I removed your duplicate post)
If I can toss my 2 cents in here. I too have always thought that it meant "equal to" in size, but upon reading again I can see some different meanings.

Substantial (according to Websters) can mean:
"being largely but not wholly that which is specified"
When you see the word "substantially" used with "equivalent" it seems like this might be the most likely meaning for the word.

Also, different materials can have different properties which means that they can offer the same protection at different thicknesses.

So, it looks to me like You have to determine what it is protecting from and them make a call from there.


Re: KO Seals #77997 08/07/01 08:27 PM
Joined: Oct 2000
Posts: 5,389
sparky Offline
well YA....
what about the plastic KO seals?

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