ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
by Rabbit. 03/20/18 08:23 PM
Recall notice: Southwire wi-fi wall switches
by sparkyinak. 03/15/18 06:03 PM
Goodman Manufacturing Recalls Modular Blowers
by Admin. 03/13/18 10:40 PM
MAAX Spas Recalls Hot Tubs and Swim Spas
by Admin. 03/13/18 10:29 PM
New in the Gallery:
Housebilding DIY wiring
SE cable question
Who's Online Now
0 registered members (), 9 guests, and 10 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Exhaust Fan Speed Control #75529
03/01/07 04:49 PM
03/01/07 04:49 PM
ShockMe77  Offline OP
Joined: Jun 2005
Posts: 821
Rahway, New Jersey
If I had a 3-phase RTU exhaust fan controlled by a 120V contactor coil, what are my options as far as speed control of the motor?

What if the control circuit operated at 24 volts?

And finally, does a motor need to be rated for variable speed for a low, medium, and high speed controlling device?

Thanks in advance.

Work Gear for Electricians and the Trades
Re: Exhaust Fan Speed Control #75530
03/01/07 05:59 PM
03/01/07 05:59 PM
LarryC  Offline
Joined: Jul 2004
Posts: 783
Winchester, NH, US
3 phase? Variable Frequency Drive.
Use the 24 VDC control signal(s) to select various pre-programmed speeds.

I do not know if the VFD can be remote mounted close to the fan or if it has to be mounted inside, close to the load center.

Larry C

Re: Exhaust Fan Speed Control #75531
03/01/07 11:11 PM
03/01/07 11:11 PM
ShockMe77  Offline OP
Joined: Jun 2005
Posts: 821
Rahway, New Jersey
Nevermind my original post. I'm not even sure what I was thinking when I asked if a control circuit could determine the speed of a motor. I was asked today about installing a speed control in a pizza place to control an exhaust fan. Just nevermind. It's all good.


2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Member Spotlight
Bay Area
Posts: 61
Joined: August 2007
Show All Member Profiles 
Top Posters(30 Days)
Trumpy 5
Admin 5
Popular Topics(Views)
244,544 Are you busy
181,668 Re: Forum
171,714 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.018s Queries: 14 (0.004s) Memory: 0.9499 MB (Peak: 1.0736 MB) Zlib enabled. Server Time: 2018-03-22 04:03:08 UTC