Sump Pump dims lights


Old 01-11-14, 07:13 AM
Thread Starter
Join Date: Dec 2013
Posts: 284
Sump Pump dims lights

I noticed when my 1/2HP sump pump turns on there is a split second dimming of lights in my kitchen. The pump is on its own circuit. The kitchen circuit and the pump are on the same phase of the service.

Is this normal?
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Old 01-11-14, 07:26 AM
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Location: USA
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Has this always happened or did it just start happening recently?

Usually this is normal --- but ---

Plug in an incandescent lamp to the other side of the service. If this gets brighter, even for a moment, when the sump pump starts (or someone uses a hair dryer) then you defintely have a problem --- with the neutrals -- and that needs immediate attention by someone (possibly you) with electrical experience.
Old 01-11-14, 07:50 AM
Join Date: Nov 2013
Posts: 281
Your loose neutral proposition is worthy of investigating but wouldnt a multimeter be a better testing device than a lightbulb?

I have a similar situation like the original poster, my sump pump does the same exact thing. And I am curious what the pros think because I always chalked it up to normal voltage drop.
Old 01-11-14, 08:08 AM
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Join Date: Dec 2013
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Well I don't have a multitester. However, I just tested a 100 watt incancdescent on a circuit on the opposite side of the service and it DID NOT brighten or dim.

So should I not worry about this then?
Old 01-11-14, 08:29 AM
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It just means that you are getting a heavy draw when the pump starts up. Has it always done it? If not, then the pump/motor may be getting old causing more current draw to start. Have you increased the load on that phase? New/more TVs, lighting, etc?

Not sure...but a new capacitor may help. Wait to see if Pro's weigh in.
Old 01-11-14, 10:16 AM
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Using a light bulb in a test like this is superior method as most homeowners don't have a meter that reads voltage changes that quick. Nothing beats the human eye for speed.

No blink on the opposite leg is good. Shows no neutral problem also.

A split second of dimming is a normal occurrence. I have it in my own house with the fridge.
All lights aren't affected the same by a voltage dip. Fluorescent lights easily flicker with a quick voltage change.

The size of the utlity supply wires and distance to the house from the transformer also plays an important part in electric stability. The further you are from the transformer.... the more the power will dip with a heavy load.

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