# fan shutdown of air handling units



## americo (Jan 21, 2010)

Air handling units are wired through variable frequency drives. At the mcc you have a main fusible disconnect switch for the respective return fan & supply fan. Do I require a contactor to accomplish fan shutdown upon fire alarm activation or can this be done at the vfd.


----------



## chomnap (Jan 21, 2010)

You can activate on VSD to saving cost and avoid any fault on VSD.
On some VSD setting if the Main Power Incoming is failed, the VFD will be tripped.

So we need to reset all the time if the Main Power failed.


----------



## Toronto Sparky (Apr 12, 2009)

Most air handlers have f/a shut down already installed with a jumper wire installed.


----------



## John Valdes (May 17, 2007)

americo said:


> Air handling units are wired through variable frequency drives. At the mcc you have a main fusible disconnect switch for the respective return fan & supply fan. Do I require a contactor to accomplish fan shutdown upon fire alarm activation or can this be done at the vfd.


This is a design issue and has no concrete answer, just a decision. How do YOU want the fire alarm to shut down the fans?
The VFD has the capability to be turned off by the alarm. Some people put contactors in front of VFD's for E-Stop which is a waste of time and materials, IMO. But that could be a company SOP. As long as you follow company SOP and it makes sense, just do what ever is the easiest way. 
I would use a fire alarm contact to shut down the VFD. Thats just me.


----------



## Mr.C (Dec 20, 2009)

Normally you wouldn't use a contactor and VFD together, no reason to. You'll be fine just using the VFD.


----------

