Hello,

I have a rooftop vent fan (3HP 480V) that the customer wants to control with a frequency drive. The panel is within sight (in the shop below). Is a disco required on the roof and prior to the drive to provide lockout capability, or does one on the roof suffice?

Also, do you guys provide additional motor protection in addition to the drive? (assuming it provides overcurrent protection)

Thanks in advance,

I don't exactly follow your installation description. However, Part IX of Article 430 identifies all your requirements for providing disconnecting means.

You will need to determine where and how you are obtaining both overload and ground-fault / short-circuit protection of the motor. It is possible this is all being doen by the VFD.

You still need a disconnect on the roof if the motor i accessible on the roof and you can use a VFD down in the control room. You also want to check that the rooftop unit will not be affected by the VFD control like built in alarm or control circuits since the VFD is altering the power.

2005 N.E.C. 430.102 B States: Must be within sight of the MOTOR Unless meets Exceptions 430.102 (B) Exception (a)or(b).
Thats the way I read it anyway.

If the motor can be serviced from the roof, the disconnect downstairs will not be in site.

I agree that why I noted must be within sign . Kinda hard to see thru the roof!
BUT what if they had a skylight?
:))

I also agree although it is in 440.14. Also was a service receptacle within 25 feet or on the roof with the equipment this is 210.63.

From a practical standpoint, such a motor need two different types of protection; overcurrent as well as overload.
Overcurrent protection is what you get from fuses and breakers. Overload protection is what you get from the heaters in the starter. It's quite possible for a VFD to provide this secondary protection.

As for the disconnect ... I wish folks would forget the fine print of the code, and look at the application from a servicing standpoint. Do you want to shut it off before you work on it - or not? If so, doesn't it make sense to have some disconnecting means at the site of the motor? Why make / expect the guy to run up and down ladders multiple times, hope his LOTO is adequate, worry about automatic controls, etc?

Thank you a little common sense is always in order.

Mike,

Article 440 does not apply to vent fans.