Thread: 4 NM-B cables under one UL Listed staple

There is a new staple appearing around here.

It is made by the Sturgen Bay Metal Products company.


The staple is call a 1/2" stacker straps for securing more than on
NM or UF cable.

The one I observed, had four NM-B 12-2/ground, (the yellow jacket),
underneath the one staple.

NM-B 12-2/ground is fuse at 20 amps.

With number of cables would the 20 amps. have to be change to a
15 amp. fuse/circuit breaker.

THANKS FOR ANY INPUT ON THIS MATTER.

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Assuming that ambient temperature isn't a factor, 4 NM-B 12-2 cables under one staple isn't a problem - 5 would be because of derating issues.

I use staples listed for 4 cables on occasion but prefer to see "stackers" because they allow the cables to be separated so derating due to the number of cables isn't an issue.

Originally Posted by Bill Kriegh

Assuming that ambient temperature isn't a factor, 4 NM-B 12-2 cables under one staple isn't a problem - 5 would be because of derating issues.

"Assuming that ambient temperature isn't a factor"

Meaning that the NM cables do not go into an attic or any area hotter than 104 degrees F.

That ambient derating factor is 0.91, apply that, then apply the 0.70 derating factor for the 8 conductors, and you get 19.11 amps derated capacity.

Which means that derating IS STILL NECESSARY, just that the outcome still meets the allowable amperage by the code, 19.11 amp rated is protected by a 20 amp breaker.

Run that NM into an attic or other hot area and you have problems after applying derating, same as if you added another NM cable - problems after applying derating (does not mean derating is not applied, just that NM-B is made to compensate for a certain amount of derating).

Originally Posted by Jerry Peck

Which means that derating IS STILL NECESSARY, just that the outcome still meets the allowable amperage by the code, 19.11 amp rated is protected by a 20 amp breaker.

If the circuit feeds receptacles used for portable cord and plug connected loads, upsizing the breaker isn't allowed.

2008 NEC ®© 240.4 Protection of Conductors.

(B) Devices Rated 800 Amperes or Less.

The next higher
standard overcurrent device rating (above the ampacity of
the conductors being protected) shall be permitted to be
used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a multioutlet
branch circuit supplying receptacles for cord and-
plug-connected portable loads.

Originally Posted by Bill Kriegh

If the circuit feeds receptacles used for portable cord and plug connected loads, upsizing the breaker isn't allowed.

Right, I forgot about that.

Which means that 4 NM cables under one staple will only work with an ambient temperature of below 95 degrees F, or basically within the conditioned thermal envelope of the house. Otherwise you would need to drop back to 3 or fewer NM cables.

Bill Kriegh

Most excellent post, so I printed it out, and file it away, under electrical.


And thank you Jerry.