# 3PH Rooftop Exhaust Fan power issues/phase monitor



## oldman (Mar 30, 2007)

We have a site that is having power issues. We don't maintain the building, we maintain one of the tenants in the building. They recently had 3 motors go in 3 roof exhaust fans. We are looking to protect these motors moving forward. 

Not sure how to do it. Was thinking a phase monitor similar to what we put on RTU's...not sure if they will work with exhaust fans.

We need to protect the new motors against voltage issues and phase loss.

Any suggestions?


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## varmit (Apr 19, 2009)

Yep, a phase monitor will do the job. Mount the monitor at the fan starters. Wire the phase monitor NC output in series with the fan starter coil circuit.


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## frenchelectrican (Mar 15, 2007)

oldman said:


> We have a site that is having power issues. We don't maintain the building, we maintain one of the tenants in the building. They recently had 3 motors go in 3 roof exhaust fans. We are looking to protect these motors moving forward.
> 
> Not sure how to do it. Was thinking a phase monitor similar to what we put on RTU's...not sure if they will work with exhaust fans.
> 
> ...


A phase monitor will work very well with this set up.

it pretty easy to hook it up. 

I would check the supply to make sure the distubation panels are good shape sometime you may find bad connection there that can affect the whole place.


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## JRaef (Mar 23, 2009)

Or just swap out the overload relays with solid state overload relays. most of those now come with phase loss protection built-in. They do a better job of it than a voltage monitor, because if the phase is lost WHILE the motor is running, it might KEEP running, and regenerate a voltage back on the lost phase that fools the phase monitor. A SSOL is looking at motor current so if a phase is lost, the current on that one phase drops to a detectable level. it's simpler too because nothing else about your wiring or control circuit needs to change, you just replace the OL relay and keep the same connections (in most cases).


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## paulengr (Oct 8, 2017)

Even if it’s a small motor most reputable motor shops don’t charge for diagnostics on a dead motor. They can look for shorted turns indicating a voltage problem (surge or grounding), mechanical issues, etc., so you can approach this more surgically and spend less time guessing. Agreed on the solid state overload and even from pricey brands like AB they are less than the cost of replacing the heaters in the overloads.

Also none of this addresses surges. A good quality surge suppressor with replaceable MOVs and an indicator light when they are used up is less than the cost of most HVAC blowers.


Sent from my iPhone using Tapatalk


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## John Valdes (May 17, 2007)

Good to see you back "oldman"!!!!!! Welcome back!
Where ya been and what have you been up too?
Young chicks I bet......lol


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