Motor Starter Locations

[steve66]

I have a project with two 20 HP exhaust fans on the roof. Should I just specifiy NEMA 3R motor starters and put them on the roof with the fans?

I always prefer to keep the motor starters inside the building, if possible, but that means adding another disconnect at the motor,

Thoughts or opinions?

 

[JoeStillman]

IMHO, put the starters indoors and tell mechanical to provide disco's with the fans.

 

[topgone]

To add, your fan motor might fail to successfully start if the motor lines are long. Starting current will be great and if the starter panel is too far up the roof, the voltage at the starter panel might get too low that the starter coil releases, stopping the motor. That is aside from the motor starting torque becoming lesser due to the voltage drop at motor terminals. It might not be enough to overcome the starting torque required to run the motor.

 

[don_resqcapt19]

To add, your fan motor might fail to successfully start if the motor lines are long. Starting current will be great and if the starter panel is too far up the roof, the voltage at the starter panel might get too low that the starter coil releases, stopping the motor. That is aside from the motor starting torque becoming lesser due to the voltage drop at motor terminals. It might not be enough to overcome the starting torque required to run the motor.

But the location of the motor starter does not change that, and long lines with excessive voltage drop reduces the starting current as it acts like a reduced voltage starter.

 

[texie]

But the location of the motor starter does not change that, and long lines with excessive voltage drop reduces the starting current as it acts like a reduced voltage starter.

True enough. But unlike a reduced voltage starter, the voltage never recovers and with some loads it may never come up to speed. But I agree, the starter location is not relevant. Also, topgone's post assumes that the control circuit is supplied by the same circuit as the load which is often not the case.

 

[topgone]

But the location of the motor starter does not change that, and long lines with excessive voltage drop reduces the starting current as it acts like a reduced voltage starter.

BTDTGTTS thing! I solved the problem of a field motor malfunctioning when the starter panel was located at the local station. The starter dropped when the voltage went down during starting of the motor. There was a longer starting time though, just like when the starter panel was near the motor. I just added a 5-core cable to take care of the start/stop buttons near the motor location.

 

[infinity]

I agree with Joe but the starters indoors and a disconnect at the fan.

 

[Jraef]

But the location of the motor starter does not change that, and long lines with excessive voltage drop reduces the starting current as it acts like a reduced voltage starter.

And loads like exhaust fans need less torque at startup than other loads, so the voltage drop at the motor is usually not a problem.

Voltage drop causing the control voltage to drop however is a real concern, because if the contactor drops out or worse yet, chatters, it can be a real serious issue.

I too prefer to see the starters inside and a disconnect outside. 3R or 4x starters outside means having to add heaters to protect against internal condensation when it’s cold, and even electro-mechanical starters are all designed around 40C (104F) operation, so on rooftops in the summer direct sun, that can become an ambient issue. They will survive on the rooftop better than things like VFDs but will not last as long as they will indoors and protected from the elements.