SCCR And Enclosure Cooling Fans

[Jsantangelo]

I have a 208 3 phase drop with a neutral to the disconnect in an enclosure. The enclosure has a 120VAC fan that is used for cooling of the enclosure. Because of the incoming power a transformer was not needed for the 120VAC required by the fan. Since the branch circuit for the fan is connected to the incoming power do I need to include it in the SCCR calculations? Also, I am having trouble finding any SCCR information on enclosure fans.

Joe Santangelo

 

[petersonra]

I have a 208 3 phase drop with a neutral to the disconnect in an enclosure. The enclosure has a 120VAC fan that is used for cooling of the enclosure. Because of the incoming power a transformer was not needed for the 120VAC required by the fan. Since the branch circuit for the fan is connected to the incoming power do I need to include it in the SCCR calculations? Also, I am having trouble finding any SCCR information on enclosure fans.

Joe Santangelo

What does UL508a say about this? I don't have my copy available right this now but I think it is covered there.

 

[templdl]

I have a 208 3 phase drop with a neutral to the disconnect in an enclosure. The enclosure has a 120VAC fan that is used for cooling of the enclosure. Because of the incoming power a transformer was not needed for the 120VAC required by the fan. Since the branch circuit for the fan is connected to the incoming power do I need to include it in the SCCR calculations? Also, I am having trouble finding any SCCR information on enclosure fans.

Joe Santangelo

Are you referring to the cooling fan motor asxa motor contribution in you SCCR? If so in my opinion I would think that it is insignificant.
But at 208v motor contribution is figured ast 50% not 100%. The motor's short circuit current contribution on the basis of motor characteristics that will give four times normal current.

 

[Jsantangelo]

Thank you for the responses. I am new to this so please bare with me. I believe that UL508a exempts enclosure air conditioners from SCCR calculations and I am wondering if a fan that is used for cooling an enclosure is exempted also?

Joe Santangelo

 

[ptonsparky]

How big is the fan?

 

[Jraef]

Even if you have 120/208V and derive your control power from one phase and neutral, you must have a control circuit OCPD of some sort, a fuse or circuit breaker. Everything down stream of that OCPD would be considered part of the control circuit and therefore not subject to inclusion in the SCCR calculations.

 

[petersonra]

SB3.2 Overcurrent protection of control circuit
SB3.2.1 For control circuits tapped from the feeder circuit, the overcurrent protection for the common
control circuit or for the primary of a control transformer or power supply shall be provided with branch
circuit protective devices having a short circuit current rating not less than the overall panel short circuit
current rating, see SB4.4.4.

I would point out that there are specific requirements for the fan itself that have to be met to use the UL SCCR calculation method. You have to follow all the rules in UL508a to be able to use their SCCR calculation method.