Ampacity of wires in an industrial control panel

[david.mullins]

I found the post at: http://forums.mikeholt.com/showthread.php?t=85410 but it seems to have a few conflicting answers.

Here are my observations:
NFPA 79 Electrical Standard for Industrial Machinery: "The provisions of this standard shall apply to the electrical/electronic equipment, apparatus, or systems of industrial machines operating from a nominal voltage of 600 volts or less, and commencing at the point of connection of the supply to the electrical equipment of the machine." I assume this means it includes the industrial control panel.

UL 508A Standard for Industrial Control Panels: This applies if we want to be listed or claim compliance as UL listed. It is good guidance, if you have it, but sizing conductors on the safe side will always keep you in the clear.

The NEC (NFPA 70) does not apply inside the panel.

My questions:
Ampacity requirements for wires are still that the over-current protective device is less than the ampacity of all downstream wires after all deratings are applied, correct?

I don't have the reference but in the NEC (maybe in NFPA 79, as well) there is a paragraph that states, as close as I can remember, "Any circuit protected by a 20A breaker or less shall be considered" ... protected for any wire size. Does that ring a bell with anyone and is that a correct interpretation?

Thanks in advance! I'm still trying to convince my boss that my time digging through the free online versions of NFPA isn't worth the $200 or so bucks.:happysad:

 

[Jraef]

This is in NFPA 79

7.2.4.2 Conductor Protection.
7.2.4.2.1 Conductors, other than flexible cords and fixture
wires, shall be protected against overcurrent in accordance
with their ampacities as specified in Section 13.5, unless otherwise
permitted in 7.2.4.2.2 through 7.2.4.2.6.
7.2.4.2.2 Conductors sizes of 18, 16, and 14 AWG shall be
considered as protected by an overcurrent device(s) of not
more than a 20-ampere rating.
7.2.4.2.3 Conductors that do not extend beyond the control
cabinet enclosure shall be considered protected by the load
branch-circuit short-circuit and ground-fault protective device(
s) where the rating of the protective device(s) is not more
than 400 percent of the ampacity of the control circuit conductor
for conductors 14 AWG and larger, or not more than
25 amperes for 18 AWG and 40 amperes for 16 AWG.

Nothing like that in UL508A however.

 

[david.mullins]

Thanks! I did later find that section, as well.

Now, if someone could just help me clarify to my manager that NFPA 79 really does apply to industrial control panels. They are dodgy about answering because they say it's a code question but I have to have a membership to get it answered. I did find this, 79:1.1.1, says: “The provisions of this standard shall apply to the electrical/electronic equipment, apparatus, or systems of industrial machines operating from a nominal voltage of 600 volts or less, and commencing at the point of connection of the supply to the electrical equipment of the machine.” In my mind, that's exactly where the ICP is but he didn't buy it. :happysad:

 

[Jraef]

You are right in that it does apply. He can, however, hang his hat on the fact that technically nobody enforces NFPA 79 when building panels, it's considered a "consensus standard"...

But, read this older thread, especially the point made by Jim Dungar at the end.
http://forums.mikeholt.com/showthread.php?t=82334
That's the operative issue. It's just like NPFA 70E in that there are no "police" for NFPA 79, but OSHA can act as the judge, jury and executioner AFTER something happens and they determine that you SHOULD have followed the consensus standard that was in existence to prevent the issue from happening.

 

[david.mullins]

I discovered a couple of things:
What standard applies depends 99.9% on the authority having jurisdiction (local or state fire marshals, inspectors, etc.). They can, in theory, require the panel to meet the NEC which then forces you to not take advantage of anything in any other applicable standard like NFPA 79.

If you call the NFPA, they will not answer a question like this, I assume for reasons of liability. They will tell you that there is material in both NFPA 70 and 79 which addresses industrial control panels. However, NFPA 70 really only addresses nameplate requirements for industrial machinery.

And the current version of NFPA 79 adds the words "Control circuit" conductors to section 7.2.4.2.2.