Lights Brighten Or Dim At Motor Start - Electrical - DIY Chatroom Home Improvement Forum

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Old 07-04-2006, 06:24 PM   #1
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lights brighten or dim at motor start

For some reason when I "search this forum" for "dim" or "brighten" I get no results so I'll go ahead and ask
When the dryer was started at this house the lights on a couple of circuits would brighten very substantially for about two seconds then go back to normal.
I wound up checking all joints and connections from inside the dryer through the breaker panel and out to the meter. I did not find a single loose or rusted or corroded or skinned or under sized joint or wire.
The dryer is three-wire properly bonded inside the dryer cabinet.
The breaker panel has the Main breaker in it and is neutral/ground bonded
The feeder and service neutrals are solidly lugged onto a common bus in the meter can
The meter can has a good solid ground wire going to a Grounding Electrode
The feeder wire is 4/0 AL

With most stuff in the house running its only drawing around 30A per leg on the service/feeder wires. The service/feeder nuetral seemed to amp only the unbalance as expected

For grins I moved the double pole 30A breaker for the dryer up one slot in the panel so as to reverse the legs that are going to the dryer.
Then the lights started dimming very substantially for about two seconds when the dryer was started. The opposite of what was happening before.

What might be going on here?
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Old 07-04-2006, 08:00 PM   #2
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Lights brightening are a classic symptom of a loose neutral. It could in the main panel, the meter can or on the power company connections.
This is serious and should be looked ASAP. The voltage is going up when this happens. It could cause serious damage to anything plugged when the voltage spikes up.

The reason I suspect the lights have now switched to dimming is that high current draw of the motor start is now on the other leg opposite to the lights. The voltage is now spiking on the other leg. When this situation exists one leg is low voltage and the other is high voltage. Plug a lamp into a receptacle on the opposite leg to the lights. You will probably see it brighten.

If you have checked all the neutral connections within your panel I would call the POCO
ASAP and explain the problem.

Last edited by joed; 07-04-2006 at 08:07 PM.
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Old 07-04-2006, 09:23 PM   #3
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what i am going to do is side with Joed about the classic event with loose netural wire.

DO NOT run the dryer or electric stove and if have electric water heater turn it off as well.

call the POCO [ power company ] asap just dont wait too long and they useally don't charge for comming out to check out their system

once the POCO did check their side then you can get the electrician to come out and check the meter socket to the main breaker box [ this part i will not let any DIY do this part due the safety reason ]

the electrician will check any loose connection on all legs to make sure it is ok

Please heed our warning it will save yourself alot of headache later

Merci, Marc
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Old 07-05-2006, 12:57 AM   #4
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Thanks guys

I'll have poco called first thing.
I knew to look for a bad neutral at first but was thrown for a loop when reversing legs caused opposite behavior.
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Old 07-07-2006, 10:06 PM   #5
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Now I know to check for such things, but I would not have thought of it before.

POCO found no problem at the pole. So we started looking again.

It turns out that someone had taken the demark end of the ground wire for the Cable TV and jambed it into the female end of a coax splitter at the Cable demark point. The other end was clamped onto the main grounding electrode conductor like normal.

I still don't understand how that caused such dramatic symptoms. I would not have thought cable had that much umph.

Anyone can shed some light on this would be great.


Last edited by geeyathink; 07-07-2006 at 10:08 PM.
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