NFPA 79 versus nec?

[rene christensen]

Hi.
Sorry for my bad english is from Sweden.
I am setting up a machine line in usa.

we recieve main power from the city into our main cabinet.
From there we are running a closed nema 4x cableway stainless, around the machine.
according to nec you are only allowed to fill it 20% and you need to correct amp rating of the cables because there are more then 30 conductors.
But i believe that this kind of installation belongs to NFPA79 machine installation.

And in NFPA 79 i can find that cable ratings are the same more then 30 conductors you need to down grade the cable to 35% of its rated value.
But it do not say anything about 20% filling.
there are no cables in the cable ducts that belongs to building installation, only cables that belongs to this internal wiring og the machine line.

So the question is: when 20% filling is not meantioned in NFPA79 is the 20% still valid or do nfpa79 remove the rule from nec. so that we can fill the cable duct more then 20% as long as we correct for heat(downgrade the cables)


Best regards.
Rene Christensen.

 

[petersonra]

nfpa79 is not a statutorily required code. in other words, it is something that one would contractually agree to use, rather than the NEC which is generally required by law.

In general, the NEC covers what is outside the control cabinet or machine envelop and not what is inside it. That does not mean that what is inside the control cabinet or machine envelope can completely ignore NEC requirements. For instance, if the control cabinet includes motor starters and over current protection for motors, it would need to abide by the NEC rules for such things for those particular motors.

Your best bet in building a control panel for the US market is to have it built by someone that can list it to UL508a requirements. There are plenty of European firms that can do this.

Your specific question is a little harder to answer directly. If the conductors are actually part of the machine assembly itself and not assembled on site, most times you would be OK. If it is something done onsite that has to be inspected by an agent of a governmental entity, they are almost certainly going to at claim it needs to meet the NEC requirements.

ETA: I would point out that the NEC uses the term "current carrying conductors". This term is not defined in the NEC so some people will claim any amount of current meets the criteria of carrying current, in effect making it mean any energized conductor. Since the code makers did not choose to use the phrase energized conductor, it seems to me they did not mean that and that signalling and control conductors are not current carrying conductors.

 

[Smart $]

I don't have a copy of 79 handy to give assessment on the 20% fill aspect.

As far as which applies, 70 or 79, depends on whether the wireway is part of the machine assembly. For example, if the machine consists of two or more sections where wiring and raceway(s) between sections is supplied by the manufacturer for field assembly, it is covered by 79. Otherwise 70 (NEC).