Industrial Control Panels

[bob3689]

I've been building and designing industrial control panels for about 15-20 yrs. Nobody has been able to answer my question. A machine control panel has a 60A 3-pole main breaker with the following sub breakers for machine motors ect. 2-20A 3pole, 1-15A 3pole, 1-10A 3pole, 3-5A 1pole. The conductors feeding the line side of the sub breakers should be what size wire? Is there a rule of thumb or an NFPA, JIC or NEC rule that governs the conductor size?

 

[bsh]

look in NFPA 79 section 13.5. It discusses conductor ampacity. Table 13.5.1 lists the ampacity for various cable sizes. It looks a lot like a copy of NEC 310.16

 

[todd99]

bob3689,

I think 409.20 is what you are looking for...Industrial Control Panel, Supply Conductors.

 

[tony_psuee]

todd99,

I think bsh is correct. I believe Article 409.20 would deal with the conductors supplying the line side of the 60A main circuit breaker.

tony

 

[todd99]

I stand corrected, I mis-read the original post. I thought that he was asking for the conductor size supplying the main breaker.

 

[Bob NH]

It's All in the Load

It's All in the Load

The principle is the same as an industrial building. Each circuit has ampacity and overcurrent protection that exceeds the load on that circuit, but the 60 Amp breaker provides margin for the total power required by the machine.

If you add all of the breakers values in a subpanel the total will almost always exceed the ampacity of the breaker and conductors supplying that panel.

 

[Jraef]

First read the definition of a "Tap Conductor" in NEC 240.2 and determine if your application qualifies. If it does, then jump to 240.4(E) for a list of othe applicable sections. Within that list is your answer, but generally you are premittied to use conductors rated for the downstream OCPD as long as the distance from the tap point to the OCPD is short. Not shown on that list however is that if the branch feeders are going to motor starters, they fall under 430.28.

 

[petersonra]

First read the definition of a "Tap Conductor" in NEC 240.2 and determine if your application qualifies. If it does, then jump to 240.4(E) for a list of other applicable sections. Within that list is your answer, but generally you are premittied to use conductors rated for the downstream OCPD as long as the distance from the tap point to the OCPD is short. Not shown on that list however is that if the branch feeders are going to motor starters, they fall under 430.28.

the tap rules apply to the premises wiring system, not the innards of a manufactured item like a control panel.

 

[templdl]

As a former application engineer if I were approached with this question I would conclude that I was not being provided with all of the information necessary to accurately address his question.
When I see "Industrial Control Panel" and 10a and 5a breakers I would need to know if the breakers are UL489 breakers or are they UL recognized carrying a UL1077 approval mark?
It is to be noted that the NEC 240.6 Standard Ampere Ratings, (A) Fuses and fixed trip breakers, 5 and 10a ratings does not appear as a standard rating. However the article does allow for non-standard ratings however they must be listed Art 110.
As such I believe that Jraef is on track if said OCPDs are not UL listed.
Also, it is of my understanding that a control panel is subject to meeting the requirements of the NEC and the inspection and approval by the AHJ which includes NFPA79, Electrical Standards for Industrial Machinery.
However, should the panel builder have received UL approval on their assembly an have been authorized to attach a UL label stating as such then the panel is not subject to inspection as it complies with art 110 as being listed and labeled.

 

[Bea]

This is an industrial control panel which will control motors table 430.72(B) applies to circuit conductors that are part control wiring.