Free/Open Air Definition

[dlamp67]

Our company sell and install standby generators. We have a product offering that is configured with the automatic transfer switch housed within the generator enclosure. This system utilizes a line side disconnect and a load side disconnect, both mounted externally onto the generator enclosure. The question is in regards to table(s) 310.16 and/or 310.17 in choosing the right size conductor based on the potenital ampacity of the transfer switch. We recently had an install fail by the AHJ stating that the conductors were undersized. The system is 480 volt, three phase. the wire chosen was based on table 310.17, 1/0 at 260 amps whereas the AHJ said the wires needed to be 3/0 at 225 amps based on table 310.16. The compartment where the transfer switch is housed is approx. 3 1/2' x 3 1/2' x 3 1/2'. The AHJ said the conductors were "not in free air", therefore he felt they were undersized. Any comments???

 

[fc]

I would have to agree with the AHJ that the wires are not in free air.
Free air to me would be wires that are in open air like the power lines on utility poles.
Your wires are in an enclosed area.

 

[barbeer]

I would not consider anything within an enclosure, raceway or inside equipment to be free air. IMHO free air refers to conductors installed with said free air movement all around and not encumbered by "walls" of enclosures or equipment.

 

[iwire]

I agree with the others and also will add that the terminals on the disconnect are not rated for use above 75 C so the for 225 amps you will need 4/0 copper.

 

[steve66]

Isn't there also something somewhere in the NEC that says something about sizing the conductors between a generator and the first circuit breaker at 125% of the rated capacity? Maybe someone else will remember exactly where that's at.

Steve

 

[charlie b]

I am not certain that the wires in question were within the jurisdiction of that Authority Having Jurisdiction. That is, I think they are beyond the scope of the NEC. These wires are part of a manufactured product, are they not? If so, does not the manufacturer have the freedom to use whatever wire sizes they wish?

 

[iwire]

Isn't there also something somewhere in the NEC that says something about sizing the conductors between a generator and the first circuit breaker at 125% of the rated capacity?

Steve the conductors between the winding and the first OPCD must be at least 115% of the nameplate rating. 445.13

In my experience those conductors have always been factory installed.

I bet the disconnects in question are on the load side of the generators OCPD already.

 

[dlamp67]

Free/Open Air Definition

I am not certain that the wires in question were within the jurisdiction of that Authority Having Jurisdiction. That is, I think they are beyond the scope of the NEC. These wires are part of a manufactured product, are they not? If so, does not the manufacturer have the freedom to use whatever wire sizes they wish?

It may be the case that the manufacturer could have that freedom if the product was UL2200 tested. Would you agree?

 

[iwire]

I am not certain that the wires in question were within the jurisdiction of that Authority Having Jurisdiction.

That is certainly a valid point, IMO we would need more info to determine that.

On the other hand the AHJ does not have to accept the equipment at all and if it is not UL listed they are likely to really look it over before they decide.

 

[Rockyd]

Our company sell and install standby generators.

The AHJ said the conductors were "not in free air", therefore he felt they were undersized.

Any comments???

Does the shop have a UL listing?

If so, are subject to NEMA specifications? I'm asking this to try and see what you set of standards you are subject to. Others may have all the pertinent information, and can give you an answer.