Panel AWG Question

[gdeters]

What NEC or UL rules apply to the AWG inside of a panel. An example would be a drive panel say a 200HP drive you are suppose to use 250kcm or a parallel to handle 240Amps but in the panel they have 3/0 from breaker to drive to drive to terminal strip. What rules or code says that this is OK?

Thank you for any information,

 

[480sparky]

If it's factory installed, it's outside the scope of the NEC.

 

[gdeters]

OK

Then can you tell me why the wire is undersized or how to safely duplicate this on another panel. Where can I go to get an answer for the question. Wire paneling is always undersized what do they undersize the wire to? Is there a standard or they just do for fun? WHere do I go to look for this information if not here.

Thank you again for any information.

 

[480sparky]

OK

Then can you tell me why the wire is undersized or how to safely duplicate this on another panel.

Build it, and contact a NRTL to send out a field inspector to put an official okee-dokee on it. Word of warning: Hang on to your checkbook!

Where can I go to get an answer for the question. Wire paneling is always undersized what do they undersize the wire to? Is there a standard or they just do for fun? WHere do I go to look for this information if not here.

NEMA and UL would be a start, but I don't think they'll have an off-the-shelf handbook just for your needs.

 

[iwire]

OK

Then can you tell me why the wire is undersized

Wire size is funny thing and many factors come into it, it is all about heat.

The NEC is very conservative and the ampacity tables are designed to be more or less foolproof.

On the other hand a manufacture can take the time to really look at the conditions of use and come up with a perfectly safe wire size that is well under what the NEC requires. The manufacture does not have to follow any wire sizing table, they can pretty much use whatever they want ........ and that does not mean it is unsafe.

In many cases after the manufacturer make the item they have it tested by a NRTL (Nationally Recognized Testing Laboratory)

how to safely duplicate this on another panel.

If you are an electrician working on equipment covered by the NEC you cannot duplicate it you will have to follow the NEC.

Wire paneling is always undersized what do they undersize the wire to?

They size it exactly how big it needs to be.

Is there a standard or they just do for fun?

As I mentioned above it is all about heat and how fast the conductor can get rid of it. With short conductor lengths what the conductor is terminated too can act as a heat sink pulling heat out of the conductor.

Also the NEC runs conductors pretty cool while a manufacture can run them hotter.

 

[Jraef]

UL 508 has it's own wire size table and allows the use of 90C wire, it differs from the NEC in a lot of cases. So when the VFD mfr had their unit UL listed, they followed the UL 508 rules for wire sizing INTERNALLY. That has no bearing on what you can or cannot use EXTERNALLY, where you are required to follow the NEC. If you are a UL508A panel shop, you can use the UL rules and list the panel as a unit. Then when installed, the internal wire sizing becomes immaterial to the NEC. If you are not a UL508A (or any other NRTL by the way) Listed Panel Shop, you cannot get away with doing that on your own, you will have to follow the NEC all the way through.

 

[petersonra]

Wiring covered under the NEC is not the same thing as wiring inside a manufactured assembly.

Both the NEC and the manufacturer of the assembly design the conductor sizing and insulation systems so that they will safely operate at the extremes of the service they will see.

It is rare that what you might see in NEC service is what would be seen in a manufactured piece of equipment. For instance, there is no conduit, and often times the conductors are able to safely dissipate more heat then if they were in a conduit.

 

[mbeatty]

As Jraef indicated, UL-508A requires that all internal panel wiring of power circuits is required to have a minimum temperature rating of 90 degrees C. Generally, our panel suppliers tend to size the internal panel wiring based on the UL-508A requirements and using NEC Table 310.17 for wires installed in "Free Air". This is just what I have seen from our suppliers.
Mark