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Old 06-08-2009, 01:33 AM   #1
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Lights dim when I turn other lights on...


Hey guys, this house has a 200 amp service, a new breaker panel and done in 98% 12/2 wiring. Was there when I moved in. House ground is 4g to water main. Whenever I turn a light or set of lights on, other lights in the house dim slighty. Im not sure wether they come back to full brightness or stay dimmed just a little.

Meter plugged into wall outlet reads 120v. When lights are turned on the current actually went up to 121 or so.

Any ideas?

Just curious but is the nutral supposed to be in conact with the ground in the box? I dont have any idea if it is, im just asking.

I'm going to call an electrician later in the week but I'm wondering if you guys have any ideas.

thanks!

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Old 06-08-2009, 06:11 AM   #2
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Lights dim when I turn other lights on...


Sounds like a loose connection somewhere. What box are you talking about. In the panel box the neut. and ground are bonded.

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Old 06-08-2009, 09:24 AM   #3
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Lights dim when I turn other lights on...


Voltage going up tell me you have loose neutral. This can be very serious and cause damage to electronics. If you turn on alre usage device like a heater it go up to 140 or 150 volts.

Call the POCO ASAP.
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Old 06-08-2009, 09:36 AM   #4
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Lights dim when I turn other lights on...


Yes I meant in the panel.

We have not moved in yet so no sensitive electronics are hooked up right now. I will check the line voltage when my air compressor fires up. Is the loose neutral usually in the panel? or could it be an issue outside of house?
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Old 06-08-2009, 11:34 AM   #5
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Lights dim when I turn other lights on...


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Is the loose neutral usually in the panel? or could it be an issue outside of house?
Yes!

If there's 5v across your bad neutral connection you'll have 125v on one side and 115v on the other.
5v at 10A might be enough to heat a bad bolted connection, if you have one of those IR meters.
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Old 06-08-2009, 12:03 PM   #6
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Lights dim when I turn other lights on...


Loose neutral could be in panel, meter base, weatherhead connection, transformer connections.

If the compressor is 240 volts it won't trigger the issue as it doesn't use the neutral. You need to test with 120 volt loads.
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Old 06-08-2009, 04:04 PM   #7
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Lights dim when I turn other lights on...


If the 3 thick wires that feed into your panel from the outside show the voltage imbalance then the problem is upstream of your panel. Measure them just upstream of the bolted connections.
Watch out for arc flash.
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Old 06-08-2009, 11:37 PM   #8
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Lights dim when I turn other lights on...


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Yes!

If there's 5v across your bad neutral connection you'll have 125v on one side and 115v on the other.
5v at 10A might be enough to heat a bad bolted connection, if you have one of those IR meters.
This is the meter I have.

Ideal 61-310


So just to be sure, I put the + lead on one of the hot cables coming in and the - on the neutral, ground or other Hot?

Thanks. I've got my friend who is a electrician coming the end of the week. I just want to see if I can get this sorted.

-josh

p.s.
I had another guy tell me today that I can touch one of the hot cables coming in as long as I dont touch the other one.... i dont know what he's smoking but that dude is nuts.
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Old 06-08-2009, 11:40 PM   #9
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Lights dim when I turn other lights on...


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Loose neutral could be in panel, meter base, weatherhead connection, transformer connections.

If the compressor is 240 volts it won't trigger the issue as it doesn't use the neutral. You need to test with 120 volt loads.
I've got a 120 compressor. Its wimpy, but it fires finish nails
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Old 06-09-2009, 05:42 AM   #10
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Lights dim when I turn other lights on...


You can touch just one cable as long as you are not touching the other or grounded but not a smart thing to do.
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Old 06-09-2009, 08:22 AM   #11
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So just to be sure, I put the + lead on one of the hot cables coming in and the - on the neutral, ground or other Hot?
Plug in a 120v hair dryer somewhere. Check from the neutral to each hot lead.
More than probably a 1v difference between the nominal 120v readings means a high resistance neutral connection. The sum of both readings have to equal the incoming 240v, which will be 240v +/- 5% or +/-10%.
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Old 06-09-2009, 08:43 AM   #12
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Lights dim when I turn other lights on...


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You can touch just one cable as long as you are not touching the other or grounded but not a smart thing to do.
Now, why would he want to do that?
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Old 06-12-2009, 08:09 AM   #13
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Lights dim when I turn other lights on...


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Originally Posted by Yoyizit View Post
Plug in a 120v hair dryer somewhere. Check from the neutral to each hot lead.
More than probably a 1v difference between the nominal 120v readings means a high resistance neutral connection. The sum of both readings have to equal the incoming 240v, which will be 240v +/- 5% or +/-10%.

OK will try. Thank you!

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