Hole Saw size

What size hole saw do I need to make a hole to mount an old work octagonal box. Your help will save me time and conversation with people I had rather not talk with in the BIG BOX store.
Jimmie
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I found out something interesting while trying to answer your question... apparently the Carlon "old work" round boxes aren't UL listed for fixture support? so I guess they are pretty much only useful for smoke detectors. Maybe use one with a fixture bar instead? that is, cut the hole, then install the fixture bar through the hole (might need a punch to "set" it) then install the box to the fixture bar. (that's what I did the one time that I had an issue like this - landlady had a ceiling box "fall down" and I used a fixture bar and regular box to fix it.)
If you go that route, the size hole saw you need should be obvious through inspection (that is, take the box and walk over to the hole saws.)
good luck,
nate
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There are more than one type of the old work plastic boxes made by Carlon. I think the type you are referring to is the one with the 3 plastic ears that rotate out. And like you say, they aren't for fixtures of any kind. But given that the stores are selling lots of them, I bet plenty wind up being used for fixtures.
They also make one that has sheet metal on each side that compresses outward when tightened. Those are rated for a reasonable number of pounds, like maybe 8 lbs I think.
 >Maybe use one with a fixture bar

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wrote:

Thanks for the info, just putting in some outdoor spot lights under the eve mounted in plywood. There are some people who walk thru my yard at night. Dont think they have bothered anything just trespassing. BTW a didnt get by the store in time to get a hole saw, used a rotozip innstead.
Jimmie
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Sounds like a much cheaper way to do it. A hole saw big enough for an electrical box is a damn big hole saw.
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On Fri, 15 Apr 2011 14:43:54 -0700 (PDT), "hr(bob) snipped-for-privacy@att.net"

Thay make them for can lights. ;-)
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Your tape measure is broken...?
R
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Yep got several tape measures, just dont have one with me, was going to stop by the store on the way home. Just hoping someone here may know. I had one I used for years and it came up missing the other day. Didnt really know what size it was just knew it was good for those blue plastic boxes at the big box store. Hate going in there but they will be the only place open when I leave work. Always prefer C&M hardware. There is a 70+ year old lady in there that has never failed to answer any question I may right off the top of her head.
Jimmie
Jimmie.
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Didnt get off work last night in time to go by the store. Worked until 0230 this morning Got the boxes installed, still dont know what size. I just drew a circle using the base of the box and roto zipped it.
Jimmie
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On Apr 15, 7:10 pm, "Stormin Mormon"

Forgot I had the rotozip. I got it for a Xmass present a couple of years ago, played with it a bit and put it away. Checked out the cost of those big hole saws, YIKES. I hadnt bought one in about 25 years.
Jimmie
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