Cable clamps and 277V

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dcspector

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Location
Burke, Virginia
I had an Electrician inform me today that in a metal box with listed internal MC cable clamps could not be used with 277 volt lighting. I said never heard that one before, or am I way out in left field somewhere.
 
Bob thanks I explained the theory of MC clad etc. I guess an Inspector in a different County out of DC informed them they could not. I knew he was mis informed and wanted to bounce this off on Ya'll. Thanks again.
 
I don't think that a manufacturer would make a box with a clamp that wasn't designed for 277 volts. Like Bob said, we use them all of the time too.
 
Here is part of the Raco catalog. See page 24. (Just the one I have been looking at.)

http://www.hubbellonline.com/wiring/raco_bell/pdf/a_steelbox.pdf

The only mention of voltage was the fact that the KOs were rated for use without a bonding jumper at below and above 250v.

However, if the carton was labeled "250v", would it be possible that the inspector thought this meant the clamp?

I had a previous employer who made us use connectors with 277v even if the boxes had clamps. Said he had failed once, and he never liked to take any chances, so he just did it all the time that way. :-?
 
Perhaps they are using 250.97 and 250.110(6) to justify the use of connectors instead of clamps.
It all seems to depend on the listing of the equipment that you are installing
 
From John's post of Hubbell

Applications: Steel Boxes​
RACO​
​
​
? high-quality steel boxes:​

?​
​
​
Are used in branch circuit wiring
to splice wires​

?​
​
​
Accommodate wiring devices,
such as switches and receptacles​

?​
​
​
Most may also serve as fixture
supports​

?​
​
​
Allow for branch circuit runs​

​
​
​

canopies or fans​

​
​
​
​

? TKO? knockouts offer greater flexibility
with RACO? patented combination
1/2" and 3/4" knockout​

?​
​
​
Stock just one product instead
of two or three​

?​
​
​
One product for the installer
to carry​

TKO​
​
​
​
? Provides Reliable
Grounding Path​

? ​
​
Independent tests conducted by
UL prove that the TKO? passes the
same high-current fault test used
to test grounding bushings and
ground lugs​

? ​
​
RACO? TKO? knockout is UL
Listed, providing bonding without
the use of bonding jumpers​

? ​
​
Suitable for bonding without any
additional bonding means around
concentric (or eccentric, TKO)
knockouts where used in circuits
above or below 250V​

? ​
​
​
This knockout does not impair the
electrical connection to ground​

Most RACO​
​
​
? Boxes Have At
Least One Tapped #10-32
Grounding Hole​

?​
​
​
The products that do not have
a grounding hole are: plenum
boxes catalog numbers 226
and 239​

Product Features:
Combination Screw Heads​
?​
​
​
Cover and clamp screws have
combination slotted/Phillips heads​


​
​
​
GENERAL INFORMATION ? STEEL BOXES AND COVERS​

A2​
RACO STEEL BOXES
 
Thanks John and Pierre,

The boxes with cable clamps per UL 514-A Suitable for use without a bonding jumper in circuits above or below 250 Volts. It is unfortunate that the previous Inspector had him change all of his boxes on his previous job.

Thanks again
 
Thanks John and Pierre,

The boxes with cable clamps per UL 514-A Suitable for use without a bonding jumper in circuits above or below 250 Volts. It is unfortunate that the previous Inspector had him change all of his boxes on his previous job.

Thanks again
 
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