Fan Power Box

[infinity]

Customer has a single phase, 120 volt, FPB with a MCA of 20.7 amps, Max OCPD 25 amps. Wants to use a 20 amp snap switch for the disconnect on a 25 amp circuit. Sound good? I said yes.

 

[Dennis Alwon]

Customer has a single phase, 120 volt, FPB with a MCA of 20.7 amps, Max OCPD 25 amps. Wants to use a 20 amp snap switch for the disconnect on a 25 amp circuit. Sound good? I said yes.

I would have said yes only if the decimal was less than .5 using 220.5(B)

 

[infinity]

For what reason? My thought was that the disco needs to 115% of the running current not the MCA.

 

[jumper]

For what reason? My thought was that the disco needs to 115% of the running current not the MCA.

430.110 seems to back this up.

 

[Dennis Alwon]

For what reason? My thought was that the disco needs to 115% of the running current not the MCA.

I am confused, how can you say yes without knowing the full load current rating of the motor?

 

[wireguru]

whats the HP rating of the motor, and of the switch? I have noticed most of the 30 amp switches carry the same HP rating of a 20 amp switch. There is also a 40 amp motor switch Leviton makes which may be more suitable for the application.

 

[jumper]

I am confused, how can you say yes without knowing the full load current rating of the motor?

Doesn't FLC x 1.25= MCA? Left book in truck.

 

[Dennis Alwon]

Doesn't FLC x 1.25= MCA? Left book in truck.

I believe you are right. Thanks. Brain is half on tonight. I guess yes would be the appropriate answer. :roll:

 

[RUWired]

Customer has a single phase, 120 volt, FPB with a MCA of 20.7 amps, Max OCPD 25 amps. Wants to use a 20 amp snap switch for the disconnect on a 25 amp circuit. Sound good? I said yes.

Would article 430.109.C apply to your installation?

(C) Stationary Motors of 2 Horsepower or Less. For stationary motors rated at 2 hp or less and 300 volts or less, the disconnecting means shall be permitted to be one of the devices specified in (1), (2), or (3):
(1) A general-use switch having an ampere rating not less than twice the full-load current rating of the motor
(2) On ac circuits, a general-use snap switch suitable only for use on ac (not general-use ac?dc snap switches) where the motor full-load current rating is not more than 80 percent of the ampere rating of the switch
(3) A listed manual motor controller having a horsepower rating not less than the rating of the motor and marked ?Suitable as Motor Disconnect?

Rick

 

[infinity]

Sorry, I proposed the question without all of the info. :roll:

I believe that a majority of the load is actually an electric heating coil so the fan might be a very small portion of the load. I'll check tomorrow to see what else the nameplate has to say.

 

[infinity]

I looked again today and I was mistaken this is actually a VAV box with an electric heating coil. The unit contains no fan.

 

[RUWired]

I looked again today and I was mistaken this is actually a VAV box with an electric heating coil. The unit contains no fan.

So that would mean that the switch needs to be rated at 125% of the full load. Also provisions of adding a lock for LOTO.(424.19)

Rick

 

[infinity]

So that would mean that the switch needs to be rated at 125% of the full load. Also provisions of adding a lock for LOTO.(424.19)

Rick

Interesting. The 125% rule was added in the 2008 NEC. Since this job is under the 2005 so it would not apply. Also I believe the locking provision is only if the the disconnect is not "within sight" of the unit.