Free Air vs 3 conductors in raceway

[David Rogers]

I am installing main feeder conductors between a main circuit breaker and a new transfer switch. The conductors are passing from the meter/main cabinet and routing to a transfer swtich. They pass through a 4" conduit nipple that is less than 24" (actually about 14") and there is one for line and load. Which do I calculate my conductor size, on free air (310-17) or not more than three conductors in a raceway (310-16).

Thanks for the help

 

[raider1]

You would use Table 310.16 because the conductors are within a raceway and enclosures (main breaker enclosure and transfer switch enclosure).

Table 310.17 is for single conductors that are run in open air such as on insulators along a building.

Chris

 

[David Rogers]

You would use Table 310.16 because the conductors are within a raceway and enclosures (main breaker enclosure and transfer switch enclosure).

Table 310.17 is for single conductors that are run in open air such as on insulators along a building.

Chris

I am a second time user and have spent a little time reading some of the other issues. I sent a message to raider 1 via a private message ability I found, but after spending a little time I've discoverd that I can get, possibly, to more people via this reply method.

I appreciate and respect raider 1's response and description, but I worked at an electrical control manufacturer for a few years many years ago. All the wiring inside the control cabinets and switchgear was installed at a free air rating (310-17). This manufacturer is a UL listed manufacturer. Based on rider 1's response, that company has been using the incorrect size conductors all these years.

Now my curiosity is up.

 

[charlie]

All the wiring inside the control cabinets and switchgear was installed at a free air rating (310-17). This manufacturer is a UL listed manufacturer. . . . that company has been using the incorrect size conductors all these years.

Actually, your logic is flawed. The manufacturers are permitted to do any type of loading they desire as long as it will pass the NRTL's tests. The NRTL (UL in this case) will test the equipment as it is built. If it passes the tests, it is good to go. The NEC is for field premises wiring and the NRTL testing is for a complete piece of equipment. :smile:

 

[bob]

The conductors are passing from the meter/main cabinet and routing to a transfer switch. They pass through a 4" conduit nipple that is less than 24" (actually about 14") and there is one for line and load. Which do I calculate my conductor size, on free air (310-17) or not more than three conductors in a raceway (310-16).

You would not have to derate the conductor for the 14" nipples. Question:
Is this in a residence? If not, how are the conductors supported.