How to use a knockout that's too big
#1
12-07-17, 12:51 PM
How to use a knockout that's too big
I have a Generac 6976 transfer switch with concentric knockouts. I couldn't get just the KO I wanted and instead wound up removing them all. So I'm left with an opening that is a little shy of 1.25" in diameter. I want to feed a single 10/3 cable into that KO. Am I correct that what I need is a 1.25--> 0.5 reducing bushing and a standard 3/8" (trade, which is 1/2" actual right?) clamp?
And then, do I just screw the bushing into the KO and the clamp into the bushing?
This is the bushing I mean: https://www.grainger.com/product/GRA...rumbCatId=2194
THanks for any input.
And then, do I just screw the bushing into the KO and the clamp into the bushing?
This is the bushing I mean: https://www.grainger.com/product/GRA...rumbCatId=2194
THanks for any input.
#2
12-07-17, 01:02 PM
Group Moderator
No..... you need what we call donuts. (reducing washers) You need two.
In this link is an 1-1/4" to 3/4". You need by 1/2" which should be available but not listed online.
Halex-1-1-4-in-x-3-4-in-Rigid-Conduit-Reducing-Washer-2-Pack
In this link is an 1-1/4" to 3/4". You need by 1/2" which should be available but not listed online.
Halex-1-1-4-in-x-3-4-in-Rigid-Conduit-Reducing-Washer-2-Pack
#3
12-07-17, 01:05 PM
The bushing would work. You can also use two flat pieces of sheet metal similar to washers to close the larger hole and still provide an opening for a smaller KO. They sell them in the electrical accessories area, but I don't know if I've ever seen one from 1.5 down to 0.5, but maybe worth checking out.
#4
12-07-17, 01:05 PM
Thanks. So I actually did buy a couple of 1 1/4 to 1/2 inch doughnuts the other day, but a) they were way too big and b) I still couldn't figure out how to use them with a 3/8" clamp (which is 1/2" in actual diameter - right?). So what do I do with the doughnut?
If you look at the photo in the link you posted, there's a round ridge around the hole in the middle. That round ridge fit perfectly inside the KO on the box.
Edit: <smacks head>. Now I get it. Put one washer inside and one outside, and clamp the clamp to them both so it stays in place. Thanks.
If you look at the photo in the link you posted, there's a round ridge around the hole in the middle. That round ridge fit perfectly inside the KO on the box.
Edit: <smacks head>. Now I get it. Put one washer inside and one outside, and clamp the clamp to them both so it stays in place. Thanks.
#5
12-07-17, 01:13 PM
Group Moderator
You use two of them. One goes on the outside of the panel and the other goes on the inside. The reduced sides face each other so that the panel is sandwiched.
#7
12-08-17, 06:15 PM
Member
So I'm left with an opening that is a little shy of 1.25" in diameter
A little shy of 1.25" would be a 1" KO. It sounds like what you need is 1" to 1/2" reducing washers, 2 of them. I've never heard them called donuts before, but that is most likely a regional thing. The 1/2" KO actually measures 7/8".
