# Proper Method for using Knockout Seals



## mwr (Dec 15, 2013)

I hope this isn't a taboo subject like pretwisting before using a wirenut... 

At work today we almost had a knock down drag out fight over knockout seals.

What is the proper way to install a 1/2" knockout seal like this, from the inside of the box with the tabs to the outside or with the tab inside the box?:









I will say I got chewed out for installing a few today from the inside of the box.. Im looking to either come back tomorrow with some good ammunition or admit defeat by reading your responses.


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## Pete m. (Nov 19, 2011)

Thats a good question. FWIW, I have always installed them from the outside in. And, I will add that I flattened the "ears" out... most of the time.:whistling2:

There probably is a "listing" thing that goes along with them but I've never been that anal.

Pete


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## Tsmil (Jul 17, 2011)

From the outside. Keep it visibly clean.


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## ponyboy (Nov 18, 2012)

Or you could throw that garbage away and use the Hoffman ones with a stud and wingnut. 

But yeah I've always installed those things from outside in


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## cultch (Aug 2, 2011)

I always went outside but come to think of it it would be easier to flatten the edges the other way around. Of course if you can just semi flatten about 2 of the lil flanges you should be gold.


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## wildleg (Apr 12, 2009)

if it's visible, sure. if it's in a clg or electric room, who the hell cares.


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## Tsmil (Jul 17, 2011)

If installed from the inside, it is possible to dislodge it and it will fall into the box or cabinet. From the outside, it can be removed but it does not fall in. Nothing like trying to remove something that has lodged in the mechanism of a disconnect.


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## mwr (Dec 15, 2013)

Doesn't look I will have a leg to stand on with those responses. FWIW I was installing from the inside of ceiling fixture box, teeth are not flattened obviously... the only way to get at the outside of the box was thru an attic. 

I refused to remove them though. Should I be doing so with either nec, installation instructions or safety in mind? And if so, please explain how omne would seal a knockout when they cant fish thriu blown in insulation to find the box on the other side?


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## Rollie73 (Sep 19, 2010)

I've seen one that was installed from the inside of a 600 volt/225 A panel......or at least what was left of it when the dumbassed maintenance guy stepped on top of the panel while trying to reach something off of a 6' ladder.

You guessed it......the KO filler fell down inside the panel under the weight of his foot....bet he crapped his pants with that bang.:laughing:


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## sbrn33 (Mar 15, 2007)

ponyboy said:


> Or you could throw that garbage away and use the Hoffman ones with a stud and wingnut.
> 
> But yeah I've always installed those things from outside in


Makes sense. Use a $12 item instead of a 30 cent one.


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## ponyboy (Nov 18, 2012)

sbrn33 said:


> Makes sense. Use a $12 item instead of a 30 cent one.


Those things are $12?!? Holy crap. I was only halfway serious.


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## Awg-Dawg (Jan 23, 2007)

mwr said:


> FWIW I was installing from the inside of ceiling fixture box, teeth are not flattened obviously... the only way to get at the outside of the box was thru an attic.


 
That's how I would have done it.


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## sbrn33 (Mar 15, 2007)

ponyboy said:


> Those things are $12?!? Holy crap. I was only halfway serious.


Yea, funny thing is sometimes it is cheaper to buy a new box. Crazy.


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## Pete m. (Nov 19, 2011)

Awg-Dawg said:


> That's how I would have done it.


Hack!!:laughing::jester:

Pete


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## cultch (Aug 2, 2011)

sbrn33 said:


> Makes sense. Use a $12 item instead of a 30 cent one.


GD are you serious? My last company would have the wing nut ones all the time. Guess no one ever looked it up. I'm out before I start bitching about that company again. I'd never seen them before then.


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## ponyboy (Nov 18, 2012)

sbrn33 said:


> Yea, funny thing is sometimes it is cheaper to buy a new box. Crazy.


I'm often forced to move or reuse old gear and damn the cost but I really prefer the Hoffman ones for larger holes like over 2". Laser dust and field mice are crafty


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## Tsmil (Jul 17, 2011)

Sorry, just have to ask.... Why did you install a box without filling them first?


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## sbrn33 (Mar 15, 2007)

Oh you are right they are much nicer. Especially in an industrial environment.
I actually stock the arlington plastic nema 1 KO seal in all sizes now. They are the ****.


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## Big R (Jan 10, 2008)

Or you could have just used this


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## mwr (Dec 15, 2013)

Does anyone know where I can find installation instructions from the manufacture on those things....? 

I need something, anything to back me tomorrow otherwise I will have a miserable day? 

And again, with safety in mind, should I eat crow and pull them out of the boxes?


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## mwr (Dec 15, 2013)

Tsmil said:


> Sorry, just have to ask.... Why did you install a box without filling them first?


Because the box was already there for like 300 years.


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## ponyboy (Nov 18, 2012)

sbrn33 said:


> Oh you are right they are much nicer. Especially in an industrial environment. I actually stock the arlington plastic nema 1 KO seal in all sizes now. They are the ****.


I really like the Bridgeport ones for 1/2 and 3/4. They are low profile and very snug


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## ponyboy (Nov 18, 2012)

mwr said:


> Does anyone know where I can find installation instructions from the manufacture on those things....? I need something, anything to back me tomorrow otherwise I will have a miserable day? And again, with safety in mind, should I eat crow and pull them out of the boxes?


 Look at the box. It might say something there. Maybe ko seals don't have install instructions for the same reason knives don't have instructions. You use the pointy end


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## Tsmil (Jul 17, 2011)

mwr said:


> Because the box was already there for like 300 years.


Ask a stupid question...... I deserved that.


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## Going_Commando (Oct 1, 2011)

ponyboy said:


> I'm often forced to move or reuse old gear and damn the cost but I really prefer the Hoffman ones for larger holes like over 2". Laser dust and field mice are crafty


I've been known to use a 4 square cover and #7 sheet metal screws. :whistling2:


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## RandyM (Apr 5, 2012)

mwr said:


> Because the box was already there for like 300 years.


Was it painted black? Then its only about 150 years old!

I have installed some on the inside of 4 squares in ceilings. Did not like the mass of wires getting stabbed by the tabs. Also peened the tabs flat depending on how it fit in the hole and where it was.


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## ponyboy (Nov 18, 2012)

Going_Commando said:


> I've been known to use a 4 square cover and #7 sheet metal screws. :whistling2:


Gotta make hay when the sun shines good buddy


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## Skyhook1 (Feb 14, 2014)

Never can find seals in the truck my helper sucks at stocking the truck.i just use fender washers and 1/4 -20 nut and bolt


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## cultch (Aug 2, 2011)

mwr said:


> Does anyone know where I can find installation instructions from the manufacture on those things....?
> 
> I need something, anything to back me tomorrow otherwise I will have a miserable day?
> 
> And again, with safety in mind, should I eat crow and pull them out of the boxes?


It's pretty standard to put them in from the outside. The only thing I can think that you could use in your defense is the time it would have taken to get your self to the location where you coulda installed them from the outside. Without knowing the exact situation I dunno. If it was gonna take waaaay longer than you mighta done what was best.


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## daveEM (Nov 18, 2012)

mwr said:


> Does anyone know where I can find installation instructions from the manufacture on those things....?
> 
> I need something, anything to back me tomorrow otherwise I will have a miserable day?
> 
> And again, with safety in mind, should I eat crow and pull them out of the boxes?


It's mostly common sense. You can tell by the design they snap in. They do not snap in with your pinkie.

What you do is you install on the outside by holding the filler with your pinkie. Reach down for your Klines. Slide klines over filler while removing pinkie. Klines are now holding the filler and you are ready to install.

You now reach down and grab your 20 Oz hammer and smack the living sh!t out of your klines. Filler cannot resist... it pops in. It is designed to reopen its little feet and grip. It's not coming out unless pried.


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## LGLS (Nov 10, 2007)

mwr said:


> I hope this isn't a taboo subject like pretwisting before using a wirenut...
> 
> At work today we almost had a knock down drag out fight over knockout seals.
> 
> ...


 Outside in. Time to eat crow.


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## MHElectric (Oct 14, 2011)

Pete m. said:


> There probably is a "listing" thing that goes along with them* but I've never been that anal.
> *
> Pete


Were gonna put that to the test real quick..

What would you say if guy used 2 washers and a nut & bolt instead of a K.O. seal? :detective:


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## A Little Short (Nov 11, 2010)

You already have your defense if the situation was as you described. Asked them if they would have crawled through the attic to stick the seal in from the outside!


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## mikeg_05 (Jan 1, 2009)

A Little Short said:


> You already have your defense if the situation was as you described. Asked them if they would have crawled through the attic to stick the seal in from the outside!


Yep! I'd tell em to lump it


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## RIVETER (Sep 26, 2009)

mwr said:


> I hope this isn't a taboo subject like pretwisting before using a wirenut...
> 
> At work today we almost had a knock down drag out fight over knockout seals.
> 
> ...


I, in the past, have been chewed out for a lot of things; I know that it is probably very hard for most on this forum to believe...but, it is true. However, what you are describing does not seem, to me, to be a mortal sin. As long as a person cannot place an "unwary" finger into an energized box it is legal AND safe.


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## Chrisibew440 (Sep 13, 2013)

Tsmil said:


> From the outside. Keep it visibly clean.


Exactly. From the inside out they look like daisies on the side of the box.


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## kbsparky (Sep 20, 2007)

Rollie73 said:


> I've seen one that was installed from the inside of a 600 volt/225 A panel......or at least what was left of it when the dumbassed maintenance guy stepped on top of the panel while trying to reach something off of a 6' ladder.
> 
> You guessed it......the KO filler fell down inside the panel under the weight of his foot....bet he crapped his pants with that bang.:laughing:





Big R said:


> Or you could have just used this
> 
> View attachment 34058


We use the Arlington plastic ones all the time. IF you can access the "outside" of the box, then that is where we insert them from. IF NOT, then push `em out from the inside, as that is where you can see them.

Either way, nothing gets blown up if one happens to fall into the guts of a hot panel.

Those old metal ones are 20th century. The new plastic ones are 21st century. Think about it.


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## halfamp (Jul 16, 2012)

If you're getting in very heated arguments about stuff like this you need to learn to pick your battles. It should've gone like this

"Why are you installing it that way?"
"Isn't that how you're supposed to do it?"
"No.."
"Ok man no problem I'll take care of it"


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## danickstr (Mar 21, 2010)

I don't think there is just one way to install it. either side is fine, although the outside in seems to be the accepted "better" way, if possible. Unless it is visible and the person paying hates it, or its in a location where it can get pushed back into the box during the use of the space, I would tell them to crawl in the attic and show you how easy it is to change.


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## 99cents (Aug 20, 2012)

Skyhook1 said:


> Never can find seals in the truck my helper sucks at stocking the truck.i just use fender washers and 1/4 -20 nut and bolt


I would have a better chance at finding a knockout filler


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## Deep Cover (Dec 8, 2012)

The one shown has no UL stamp on it so I wouldn't use it. Not to mention, I though only homeowners tried to use that style. Buy the plastic snap in ones, then can be installed from either side, and they have the UL stamp.


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## Big John (May 23, 2010)

ponyboy said:


> Those things are $12?!? Holy crap.


 _Pony _will be back later. He's gotta take a round up a bunch of, uh, "miscellaneous hardware" and put it back on the stockroom shelves when nobody is looking.


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## mwr (Dec 15, 2013)

> The one shown has no UL stamp on it so I wouldn't use it. Not to mention, I though only homeowners tried to use that style


I believe they are made by Raco. Its what we get at the supply house, same manufacture of everything else metal we use. I would assume they have the UL listing (although there is no embossed stamp on it). They most certainly dont have installation instructions which would have ended this debate on the spot.....

So safety will be the main debating point today, they will claim it will come loose in the box. Nobody seemed to touch on this.... from a safety standpoint, in a ceiling box with 1/2" knockouts, do I need to replace this?

Of course if the boss tells me otherwise it will have to go but if some other grunt like myself starts talking about safety I wont be changing it unless you guys think otherwise. 

ps- For the guy suggesting plastic ones, if I would buy a bag of those on my way in to work and installed one of those today I would get my balls broken over using plastic in a metal box.... I cant win.


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## Pete m. (Nov 19, 2011)

MHElectric said:


> Were gonna put that to the test real quick..
> 
> What would you say if guy used 2 washers and a nut & bolt instead of a K.O. seal? :detective:


I would say: "What the hell are you thinking?!?!? That has to be the most hack install I have ever seen during my meek existense here on earth!! Who, in their right mind, would ever do something so assinine?!?!"

Followed by: "Here's your green tag."

Pete


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## brian john (Mar 11, 2007)

Duct tape out side the box.


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## retiredsparktech (Mar 8, 2011)

Deep Cover said:


> The one shown has no UL stamp on it so I wouldn't use it. Not to mention, I though only homeowners tried to use that style. Buy the plastic snap in ones, then can be installed from either side, and they have the UL stamp.


I always understood the KO plug had to be made of the same material and thickness of the box or enclosure. The ones we always used had a screw and a strap that located in the KO. IIRC, they were made by Appleton or OZ-Gedney. :thumbsup:


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## Hack Work (Dec 29, 2013)

Deep Cover said:


> The one shown has no UL stamp on it so I wouldn't use it.


Why do you need or want a UL stamp?


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## Deep Cover (Dec 8, 2012)

Hack Work said:


> Why do you need or want a UL stamp?


I'll cite 110.21


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## NacBooster29 (Oct 25, 2010)

If anybody on my job ever put one inside the box. There would be a fight. 
In the case you described I may let it slide.


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## sbrn33 (Mar 15, 2007)

retiredsparktech said:


> I always understood the KO plug had to be made of the same material and thickness of the box or enclosure. The ones we always used had a screw and a strap that located in the KO. IIRC, they were made by Appleton or OZ-Gedney. :thumbsup:


Can I use a plastic blank on a metal box?


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## sparky402 (Oct 15, 2013)

sbrn33 said:


> Can I use a plastic blank on a metal box?


Idk but i had to 1 day in the middle of nowhere. ::


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## Hack Work (Dec 29, 2013)

Deep Cover said:


> I'll cite 110.21


Is a KO seal considered "electrical equipment"?

Do you only install screws, nuts, washers with UL listings on each?

You do realize that you can code compliantly use a blank piece of steel or a pair of washers or many other solutions (that aren't UL listed) to seal a hole in a box, right?


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## retiredsparktech (Mar 8, 2011)

sbrn33 said:


> Can I use a plastic blank on a metal box?


We used them at one time, when we were relocating lighting fixtures. The only one that would notice it, would be an electrician.
The only time, that permits were pulled, is when a contractor did the work.


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## Deep Cover (Dec 8, 2012)

Hack Work said:


> Is a KO seal considered "electrical equipment"? Do you only install screws, nuts, washers with UL listings on each? You do realize that you can code compliantly use a blank piece of steel or a pair of washers or many other solutions (that aren't UL listed) to seal a hole in a box, right?


I say yes, but my only justification for this is that some manufacturers do spend the $$ for the listing.


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## uconduit (Jun 6, 2012)

For snap-in k.o. Seals: just press the ko seal against the outside of the enclosure and strike with a blunt object until it snaps in. Only install from outside in and don't spread out the little petals or anything like that. 

For 3-piece: align properly and tighten with screwdriver. Easier said than done but that's basically it. And never install from the inside if the outside is accessible, but if it's not accessible (for whatever reason) then installing from the inside is just fine. 

Anything wrong with that?


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## Hack Work (Dec 29, 2013)

Deep Cover said:


> I say yes, but my only justification for this is that some manufacturers do spend the $$ for the listing.


So you only use screws, nuts, washers, etc. with a UL listing on it?


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## Jlarson (Jun 28, 2009)

Yeah my pop in seals come in nondescript cardboard boxes with nothing more then a bar code sticker, no UL bullschit.

Listed seals :lol: :lol: :lol:


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## Hack Work (Dec 29, 2013)

Jlarson said:


> Yeah my pop in seals come in nondescript cardboard boxes with nothing more then a bar code sticker, no UL bullschit.
> 
> Listed seals :lol: :lol: :lol:


I buy KO seals by the roll.


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## ponyboy (Nov 18, 2012)

Big John said:


> Pony will be back later. He's gotta take a round up a bunch of, uh, "miscellaneous hardware" and put it back on the stockroom shelves when nobody is looking.


Shoot man, tomorrow I'll purposefully knock out the wrong KO from a 4 square just to use a $12 one. I don't care about nothing


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## kbsparky (Sep 20, 2007)

mwr said:


> .... ps- For the guy suggesting plastic ones, if I would buy a bag of those on my way in to work and installed one of those today I would get my balls broken over using plastic in a metal box.... I cant win.





retiredsparktech said:


> I always understood the KO plug had to be made of the same material and thickness of the box or enclosure. The ones we always used had a screw and a strap that located in the KO. IIRC, they were made by Appleton or OZ-Gedney. :thumbsup:





sbrn33 said:


> Can I use a plastic blank on a metal box?


Why not? And for those who are saying different, cite me the section in the _Code_ where you _can't._

You ain't going to find it.

You can use plastic connectors in a metal box, why not plastic knockout fillers? Even the breaker blanks are plastic these days!!


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## Deep Cover (Dec 8, 2012)

Hack Work said:


> So you only use screws, nuts, washers, etc. with a UL listing on it?


Probably not, but I wouldn't consider nuts/screws electrical equipment.


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## ponyboy (Nov 18, 2012)

Deep Cover said:


> Probably not, but I wouldn't consider nuts/screws electrical equipment.


Fender washer method will work up to 1 1/2" trade size though!!


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## Deep Cover (Dec 8, 2012)

The way I look at it is that if the box and cover need a listing, what you use to close an open KO should be listed as well.


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## Hack Work (Dec 29, 2013)

Deep Cover said:


> The way I look at it is that if the box and cover need a listing, what you use to close an open KO should be listed as well.


But the code doesn't require that.



> 110.12 (A) Unused Openings. Unused openings, other than those
> intended for the operation of equipment, those intended for
> mounting purposes, or those permitted as part of the design
> for listed equipment, shall be closed to afford protection substantially
> equivalent to the wall of the equipment.


\


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## Southeast Power (Jan 18, 2009)

mwr said:


> I hope this isn't a taboo subject like pretwisting before using a wirenut...
> 
> At work today we almost had a knock down drag out fight over knockout seals.
> 
> ...


I could see putting them in the on the inside if it were the bottom of a box just due to the whole gravity thing.
Otherwise, its just aesthetics.


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## local134gt (Dec 24, 2008)

sbrn33 said:


> makes sense. Use a $12 item instead of a 30 cent one.


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## Deep Cover (Dec 8, 2012)

Hack Work said:


> But the code doesn't require that. \


I will refer you back to 110.21


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## Hack Work (Dec 29, 2013)

Deep Cover said:


> I will refer you back to 110.21


You have nothing to support a KO seal being electrical equipment while a washer or screw isn't.

110.12 (A) clearly allows you to use unlisted items for that purpose.


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## Maple_Syrup25 (Nov 20, 2012)

We use these as well as the classic filler. They are a little more expensive though


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## Jordan.M (Dec 31, 2013)

I have always installed from the outside in, and usually flatten out the "ears" to make sure it gets the best seal/connection possible. Best not to knock out the wrong holes on a box though.:thumbup:


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## Deep Cover (Dec 8, 2012)

Hack Work said:


> You have nothing to support a KO seal being electrical equipment while a washer or screw isn't.
> 
> 110.12 (A) clearly allows you to use unlisted items for that purpose.


Nuts/Bolts/Washers are clearly fasteners. A KO seal is not a fastener. 



> Equipment. A general term, including *fittings*, devices, appliances,luminaires, apparatus, machinery, and the like used as a
> part of, or in connection with, an electrical installation.





> Fitting. An accessory such as a locknut, bushing, or other
> part of a wiring system that is intended primarily to perform
> a mechanical rather than an electrical function.


If I had to categorize a KO seal, it would be a fitting.


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## Holt (Jun 20, 2011)

I would rather fall out then in


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## papaotis (Jun 8, 2013)

ive done them both ways, depending on convenience, but i can see a couple good reasons to bend out at least a few 'ears' on the ear side, no matter which way it goes in:whistling2:


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## cdnelectrician (Mar 14, 2008)

I would never install them inside out! 3/4 and up I bend two of the ears over because they don't ever fit tightly. 1/2 I put it in place, hold a screwdriver handle over it and whack it with my pliers.


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## Jlarson (Jun 28, 2009)

Hack Work said:


> I buy KO seals by the roll.


I use black gorilla tape on some rack mounted stuff to cover up square connector cut outs.


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## cultch (Aug 2, 2011)

local134gt said:


> View attachment 34131


I didn't think s #'s sounded right. Thanks for posting.


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## ponyboy (Nov 18, 2012)

cultch said:


> I didn't think s #'s sounded right. Thanks for posting.


But that's not the same design as the Hoffman ones. First of all it's ugly and secondly I bet it doesn't have a gasket


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## retiredsparktech (Mar 8, 2011)

ponyboy said:


> But that's not the same design as the Hoffman ones. First of all it's ugly and secondly I bet it doesn't have a gasket


 We only used the Hoffmanns in the operator's control stations or hoist pendants. Why would you need a gasket for the KO plug applications. We always used the kind shown in entry #66. :thumbsup:


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## manchestersparky (Mar 25, 2007)

ponyboy said:


> Fender washer method will work up to 1 1/2" trade size though!!
> 
> 
> View attachment 34122


Then you start using 8B covers !


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## Gnome (Dec 25, 2013)

local134gt said:


> View attachment 34131


Never seen that style before; that's pretty slick. I wonder if they have a CSA listing.


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## kinglew (Mar 16, 2008)

outside only


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## LightsOn81 (Jan 6, 2012)

I put em In with the little ears things out and then flatten it. Those flaps are sharp and could easily nick a wire if someone ain't being careful. If a box is exposed and I knock it out wrong, ill set it to the side and use a new box then use the messed up box elsewhere.


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