Lights Dim when motor kicks on

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Matty

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Is it normal for lights to dim for an instantaneous second when motor kicks on due to inrush current. I know this is normal in residential with AC condenser, does this apply to commercial with motors such as elevators or other motors?
 
I suppose it would depend on the facility and the motors, but I would say mostly it is not normal for the lights to dim when motors come on.
 
One more time

Light flicker (dimming and restoration of light to near preflicker level) of lights from motor inrush) is a byproduct of several factors and generally is difficult to over come.

AC motor loads (in particular compressors) but all motor loads have inrush currents. These inrush currents result in voltage drop in the branch circuit, panel bus, service laterals, utility transformer and possibility the utility HV feeders.

Flicker is in addition user dependent; some people are more susceptible to flicker. For some reason flicker seems to bother women more that men (based upon personal experience).

A Voltage Drop (VD) as little as 3 volts on a nominal 120 VAC system is noticeable (by me), 2.5% VD.

We have had cases were the VD was all a byproduct of primarily single phase 120 VAC loads, in these cases we were able to put the lighting on L1 and all the motor loads on L2, the HVAC compressors were something the homeowner had to live with. This minimizes the flicker.


To test for this VD and resulting flicker to determine the source of the inrush, use a min max amp clamp and min max multimeter at the main service watch the lights(it may take two workers) and correlate to the meters.
 
Hey Matty listen to Brian.. and just a tid bit of info change your font when posting here. Most of us are not hard of hearing. Also, I have had a weak neutral connection that caused the flickering.
 
Along with Brian's comments.....check branch and feeder connections, and check voltage at both branch and feeder locations with the motor running and/or starting, and then without the motor running . If the difference is present, you could have a conductor sizing issue resulting in voltage drop....

If you dont know how to figure VD, there is a great excel based calculator on Mike Holts home page listed under "free stuff"

and, BTW, I like the large font, I was able to read it without my specs...ha ha
 
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I need to modify this stock post to include a loose neutral. Light flicker in its self is not all bad, though annoying. But a loose neutral can be devastating.

Mule I am pretty lazy I usually start with the service and work down. Espically if this is a whole house flicker.
 
Is it normal for lights to dim for an instantaneous second when motor kicks on due to inrush current. I know this is normal in residential with AC condenser, does this apply to commercial with motors such as elevators or other motors?

So the answer to this question is: yes, it is normal for lights to dim in commercial installations due the the starting of elevators and other motors?

I don't think I agree with that.
 
. . . I don't think I agree with that.
I think you might want to do some voltage drop calculations before making that comment. Keep in mind the impedance of the serving transformer when doing your calculations and the LR current of the motor that is causing the flicker. :)
 
I am not disputing the large starting current of the motors or the voltage drop. I dispute the discernable routine or "normal" dimming of lights due to motor starting in commercial installations.

Are you saying that HID or fluorescent lighting in shopping malls or other commercial facilities is noticably dimmed by the starting of elevators ?
 
I am not disputing the large starting current of the motors or the voltage drop. I dispute the discernable routine or "normal" dimming of lights due to motor starting in commercial installations.

Are you saying that HID or fluorescent lighting in shopping malls or other commercial facilities is noticeably dimmed by the starting of elevators ?


Bit off the topic but a few years ago we had a reduce voltage starter burn up on a 250 HP 208 VAC motor. This was during a cold snap and this was the only HVAC fan for a 8 story building.

I modified the starter for across line start, set up a remote start and brought the motor on line. Lights flickered, motor whines, belts screamed, but we got the heat on. I told the management that they should keep it on line 24X7 while we obtained parts and pray there was no utility outages.
 
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