Lights Dimming upon motor starting

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Npstewart

Senior Member
We got a call recently from someone who owns a home and is having issues with their lights dimming when a vacuum is started or any other motor. The lights typically dim to about 50% until the load is removed. The power company has visited the site several times and put a recorder on their service. They found that before the meter there was no issue, but after the meter they found that there were several low voltage dips around 30 times a day. They found a voltage present in the neutral of about 14 volts and the phase voltage to be 98 (I believe this is when the load is applied). Important Note: The lights do not return to 100% until the load is removed from the circuit.

Typically, I would think this is a power company issue but after hearing the info on the recorder I think the problem would have to be that the neutral isn't properly bonded to the ground or the house is insufficiently grounded. I hear about this issue a lot but it always seemed to be solved by the power company. Anyone have experience with this?
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
We got a call recently from someone who owns a home and is having issues with their lights dimming when a vacuum is started or any other motor. The lights typically dim to about 50% until the load is removed. The power company has visited the site several times and put a recorder on their service. They found that before the meter there was no issue, but after the meter they found that there were several low voltage dips around 30 times a day. They found a voltage present in the neutral of about 14 volts and the phase voltage to be 98 (I believe this is when the load is applied). Important Note: The lights do not return to 100% until the load is removed from the circuit.

Typically, I would think this is a power company issue but after hearing the info on the recorder I think the problem would have to be that the neutral isn't properly bonded to the ground or the house is insufficiently grounded. I hear about this issue a lot but it always seemed to be solved by the power company. Anyone have experience with this?

It's more likely a loose neutral connection somewhere. See if it happens on all circuits, or just on certain ones.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
We got a call recently from someone who owns a home and is having issues with their lights dimming when a vacuum is started or any other motor. The lights typically dim to about 50% until the load is removed. The power company has visited the site several times and put a recorder on their service. They found that before the meter there was no issue, but after the meter they found that there were several low voltage dips around 30 times a day. They found a voltage present in the neutral of about 14 volts and the phase voltage to be 98 (I believe this is when the load is applied). Important Note: The lights do not return to 100% until the load is removed from the circuit.

Typically, I would think this is a power company issue but after hearing the info on the recorder I think the problem would have to be that the neutral isn't properly bonded to the ground or the house is insufficiently grounded. I hear about this issue a lot but it always seemed to be solved by the power company. Anyone have experience with this?

All the time. Start at the meter base and check all the connections back to the last panel. Don't just look at them, clean them and reinstall if necessary. Leaky meterbase or outside disconnect is a likerly place.
 

Besoeker

Senior Member
Location
UK
It's more likely a loose neutral connection somewhere. See if it happens on all circuits, or just on certain ones.
If it was a loose neutral, loose enough to cause voltage drop at the levels being described, wouldn't the dissipated power from it display evidence of overheating?
 

Hv&Lv

Senior Member
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-
Occupation
Engineer/Technician
If it was a loose neutral, loose enough to cause voltage drop at the levels being described, wouldn't the dissipated power from it display evidence of overheating?

Yes, but the problem is the evidence can be hidden by the aluminum wire. I have found many neutrals burnt on the backside of the wire, showing very little if any evidence of heat on the visible side.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
Typically a loose neutral will result in low voltage on one leg and high voltage on the other. It can be a serious problem causing damage to the equipment on the high voltage side.
Did the power company apply a load to do their testing?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Typically a loose neutral will result in low voltage on one leg and high voltage on the other. It can be a serious problem causing damage to the equipment on the high voltage side.
Did the power company apply a load to do their testing?

We have a recorder that we connect to our side of the meter, and the load is applied by the homeowner when they use various appliances. The readings are then downloaded and analyzed. Normally this isn't done to a residential service until we have exhausted all options to be nice and tell the homeowner not to call us again until an electrician has fixed thier problem.

As a side note, I used to try to fix these problems as they came up. Was told to stop, and if I liked my job, not to solicit any type of side work. So, If I knew where the problem was, I couldn't fix it, even under my own license. I could only tell the homeowner what the problem was, then to top it off, I had to go home while someone made easy money fixing a simple problem. Of course, in today's economy, I'm not complaining, just sayin...:p
 
T

T.M.Haja Sahib

Guest
When was the wiring of the house under voltage problem done? Aged wiring may be the cause.........
 

gar

Senior Member
120217-0802 EST

Npstewart:

A voltmeter and a 1500 W heater should allow you to fairly quickly run some tests and find the problem or problems. You only need very basic electrical circuit theory to do this.

Do you need further information on how to proceed?

.
 
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