What size Cable Clamp for junction box

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Burgy

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Hello. I am adding some junction boxes in my basement. The metal boxes have a 1/2" hole and also a 1" hole on opposite sides. For the 1" hole I had thought that a 1" cable clamp would work. I ordered a few and to my surprise, the diameter is just a tad to big. Do you know if there is a cable clamp that will work with a 1" hole?

Thank you.
 

Snoonyb

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Cable clamps are, generally, packaged in a flex pkg. so that, for trial & error, you, could punch the K/O on the box and again, thru trial & error, find a clamp that fits the K/O, but you need to be in the vendors estab.
 

Guzzle

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I read where a Romex twin screw clamp that they call 3/8 fits in a 7/8 hole. This is worse than calling a 1.5 x 3.5 a 2x4. :(

Fun with a digital micrometer & basement elec. H/W.
Hole size 0.891”, clamp needs min diameter hole of 0.795” & max of 0.923”
Hole size 1.098”, clamp needs min diameter hole of 1.042” & max of 1.318”

0.891" X 32 = 28.5, call it 28/32 = 14/16 = 7/8" give or take.
1.098" x 32 = 35, call 36/32, 1" + 4/32 = 1-1/8"

(0.795” + 0.923”)/2 = 0.895", x 32= 27.4/32, call it 14/16, = 7/8.
(1.042” & 1.318)/2 = 1.18", 0.18 x 32 = 6/32 = 3/16, so 1-3/16.
 
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Guzzle

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It seems to be useless to know what they say is a clamp size.

Therefore, I recommend:
Measure the knockout circle in your house box with a ruler
Find a knockout circle of the same diameter in a junction box at the store
Hold a store clamp up to this hole & eyeball whether it fits or not.

You never need to know actual hole & clamp sizes, just compatibility.
 

kok328

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Are you sure it's not a 3/4" KO? Those are more common combination with boxes.
 

Guzzle

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I can't find a link with the mech drawings for these twin screw clamps, nominal dims vs actual dims. :(

Assuming they round to the nearest 1/8" & assuming all nominal dims,
for my large clamp, the hole for the cable is 3/4" & the mating hole size could be 1-1/4" and
for my small clamp, the hole for the cable is 5/8" & the mating hole size is 7/8".

There's also a main panel KO that measures 1-3/4". IDK what the clamp for this hole measures.

I don't see a pattern yet, except the thread depth is more for the large clamp, prob. because larger cables put more torque on the clamp.
 
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Guzzle

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Was at The HD & thought I would check on their
twin screw
cable clamp nomenclature for
"Romex type" cable vs
real life inches.

No help.

This is getting personal for me! :D Maybe the NSA can crack this code.
 

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