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Old 11-01-2010, 11:35 AM   #1
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Lights flickering, voltage fluctuations throughout house


Hello,

I am having an issue with lights flickering intermittently, as well as voltage fluctuations in receptacles whenever I turn lights on/off. I have tried to do some debugging which I will outline here.

- I'm having this issue most of the time, but not 100% of the time. It seems to go away for short periods of time occasionally.

-I've measured the voltage (hot to neutral) at the receptacles and it can vary from 110 V to 130V. This voltage can change as much as 13V on the same outlet if I switch lights on/off in the same or other rooms of the house.

- I'm also seeing ~12V between neutral and ground right now.

- I have a surge protector which indicates when the outlet is "not grounded". The indicator lights up whenever I'm having the issue, and turns off when the issue goes away.

Lighting and receptacle wiring are on a subpanel, with the main panel being used for large appliances, etc.

I called the power company last week and they said they would only come out if I was having an issue with my 240V appliances. They said that the flickering light issue must be internal to my house.

Was the power company's response reasonable?

Any suggestions would be greatly appreciated.

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Old 11-01-2010, 11:44 AM   #2
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Lights flickering, voltage fluctuations throughout house


Quote:
- I'm also seeing ~12V between neutral and ground right now.

- Lighting and receptacle wiring are on a subpanel, with the main panel being used for large appliances, etc.
Start by checking the neutral between the subpanel and the main panel. The connections could be loose. Turn off the main breaker for this..

While you are at it, retorque all the connections. To do this screw it in moderately tight if necessary, then unscrew it a quarter turn, then tighten it firmly Do not use tremendous strength. You can leave the main breaker on and turn each breaker off when tightening it screw.

Don't touch the big screws for the main power feed, let an electrician do those.
Quote:
I called the power company last week and they said they would only come out if I was having an issue with my 240V appliances. They said that the flickering light issue must be internal to my house.
Not exactly correct. If the neutral is broken outside the house the flickering light issue can still occur. Also if the neutral is broken, some 240 volt appliances (those with no 120 volt internals) will still work normally.

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Last edited by AllanJ; 11-01-2010 at 11:49 AM.
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Old 11-01-2010, 12:16 PM   #3
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Lights flickering, voltage fluctuations throughout house


Thank you for the quick response. I'll start with the neutral connection on the subpanel.

As long as the main breaker is off, there should be no hot wires on the subpanel, correct? I understand the incoming wires on the main panel will still be hot, though.
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Old 11-01-2010, 01:43 PM   #4
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Lights flickering, voltage fluctuations throughout house


As long as you shut off the breaker feeding the subpanel (or the main breaker in your main panel) your subpanel should be completely dead.

If your subpanel has a main breaker in it, turning that breaker off will de-energize the whole sub EXCEPT the two screws on that breaker. If you want the whole thing dead, cut off power in your main panel instead.

You can use a non-contact tester or a multimeter to verify this.
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Old 11-01-2010, 01:55 PM   #5
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Lights flickering, voltage fluctuations throughout house


Look for something different.....like some corrosian or discolor of the insulation at the connection (any and all connections). POCO is not always right......(like after they changed thier transformer on the pole everything worked just fine) This has happened to me more than once.
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Old 11-02-2010, 12:40 PM   #6
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Lights flickering, voltage fluctuations throughout house


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Originally Posted by AllanJ View Post
Start by checking the neutral between the subpanel and the main panel. The connections could be loose. Turn off the main breaker for this..
AllanJ was right on the money. The neutral connection coming from the subpanel was loose at the main panel. I measured a 30 Ohm resistance (with the power completely off) between the subpanel neutral and the neutral bus bar at the main panel. See attached pic.

I loosened the screw and re-tightened without taking the thick neutral wire out. Resistance measurement between wire and bus bar came at 0 Ohms. This resolved most of the issue. However, under high load conditions (when most of the lights in the house are on, or when a vacuum cleaner is turned on), I see some flickering still.

Maybe I didn't tighten enough? Should I take the thick wire completely out and check its condition at the point of connection? Time to call an electrician?

Thanks for all your input again!

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Old 11-02-2010, 12:48 PM   #7
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Lights flickering, voltage fluctuations throughout house


Ideally you should take the wire out and scrape off any discoloration, also insert a sliver of sandpaper in the hole to scrape off discoloration inside.

However loosening and retightening a second time usually jostles the wire inside enough to make a good enough contact.

Check the other end of the wire down in the subpanel. Also tighten other screw connections including those that hold parts of the panel to each other.
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Last edited by AllanJ; 11-02-2010 at 12:50 PM.
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Old 11-02-2010, 01:21 PM   #8
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Lights flickering, voltage fluctuations throughout house


Make SURE the main breaker is off if you remove that neutral wire. Otherwise you could severely damage every 120v device in your house.

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