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Old 12-17-2011, 02:19 PM   #1
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Dimming Lights and Possible Neutral Problem


I’ve been reading through a lot of forums about dimming lights and have been able to narrow it down to what I believe is a bad neutral from the POCO but wanted to see what you guys think. The POCO says everything is within specs though. They have been out 4-5 times and the last guy that came out twice specializes in the hard to find problems. Below is some info and details I’ve found. When I turn on something with a larger load my voltage goes up on phase. See below for specs.

We have been in the house for about a year and have this issue since day one.
House was built in 1982 and added onto in 2006.
200 Amp service with 1/0 90C aluminum wire (neutral is smaller) underground feed (this seems small for 200 amp service?) I have 3/0 copper going from the meter to the breaker box.
The breaker box and breakers are new and all lugs have been tightened.
Neighbors don’t seem to have any problems.
When I run the vacuum, laser printer tools, AC, etc the lights in the entire house briefly dim. I checked to see what kind of voltage drops I was getting. Using a digital Fluke meter I ran voltage test as the breaker panel and meter box. I get the same voltage changes before and after the meter and breaker panel.

For the test I used a 120 Volt table saw which per my amp meter draws about 14 amps running and during startup the peak is 78 amps. Each phase was using about 10 amps from other appliance etc.

No big load 241 volts
Start the table saw it drops to 239 volts
While table saw is running 241 volts

One phase: Yellow
No big load 120 volts
Start the table saw it when up to 125 volts (yup it went up)
While table saw is running 121 volts

Other phase: Blue
No big load 121 volts
Start the table saw it drops to 112 volts
While table saw is running 120 volts

The POCO had a meter on the house for a number of days but they said everything looked good. They did find a source which was drawing 20 amps constantly every 10 minutes which I tracked down to be a bad attic fan.
From what I’ve read I should not see one phase go up in voltage, right?
What else am I missing or should I check? Ground?
Assuming it’s pointing towards a bad neutral with the POCO how can I prove to them the problem is with them.

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Last edited by carfan87; 12-17-2011 at 05:51 PM.
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Old 12-17-2011, 02:34 PM   #2
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Dimming Lights and Possible Neutral Problem


You don't have enough power to run what you're running.

That dimming of the lights, etc. means you have too many electronics/powered devices on. your house can't supply that much power. Consider upgrading your homes power unit(s). As far as size of aluminum cable, for your main feed into your home, it should be a #6. (6 AWG)

See how many amps is pumping into your home, vs how many amps you're using.

Checking electrical devices, you should have nothing that exceeds 5,000 amps, and that would be your water heater or oven. Or you have one insane table saw.

Checking how many amps your circuit is rated will go a long way. As previously stated, you have too many electronics running for your home to power. Consider upgrading. or using less power.

Any devices that just state voltage instead of amperage, you can find the amperage via Wattage divided by Volts, or Volts divided by Resistance (Ohms)

Also, can't remember what it's called, but there is a plug-in you can purchase from home depot with three lights built into it, use it and plug it into all of your outlets, and determine which ones are wired in reverse, have no grounds, etc. etc. etc. There will be a legend on it that states which lights will light up to indicate what with each individual outlet in your home. If it's bad neutral wiring in any recepticles that will find it.

Also, regarding the lights etc. briefly dimming, sometimes that's just because of the surge of power a vacuum, tablesaw, etc. needs to start running, and the homes circuit is adjusting to that. It's very, very common.

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Last edited by BigGuy01; 12-17-2011 at 02:39 PM.
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Old 12-17-2011, 05:25 PM   #3
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Dimming Lights and Possible Neutral Problem


At that time I was only drawing 10 amps on each phase. Then throw the tablesaw on and I'm at 34 amps total. I would hope 1/0 aluminum could handle that unless of course the wire is going bad. When the well which is 240v turns on I don't notice dimming.

I turned all of the lights on in the houes which totaled about 50 amps and then turned on the tablesaw. The lights through out the house dimmed a lot but my voltage drops were only about volt more than before. In my past homes when I turned on the tablesaw the lights did not dim. Also when we vacuum the lights did not dim. Since I have a 200 amp breaker pannel I figured they also should not dim. I'm begining to wonder if the previous owners upgraded to 200 amp service but the POCO did not upgraded the serice to the house. When I turned on all of the lights I could hear the breakers making a humming noise. I've never heard that in the past. Is that normal?
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Old 12-17-2011, 05:42 PM   #4
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Dimming Lights and Possible Neutral Problem


Well the poco is known to use the same wire for 100 and 200 amp services (in my area at least). Now I've heard once for a senior electrician that If there is real good grounding system in place it will reduce the dimming when big appliances start up. I can't explain why that would be or if it's true, just figured I would put it out there
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Old 12-17-2011, 05:46 PM   #5
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Dimming Lights and Possible Neutral Problem


I assume you have a typo, and the voltage on the first leg drops to 115V when starting the saw, not 125V. The real question is what happens to the voltage on the leg that the table saw is NOT connected to. I don't think you posted that information, unless I'm missing something. At first glance, however,t he voltage drop you are observing does not appear abnormal. I would say there's nothing really wrong here. Some dimming of lights is normal when a huge load comes on-line. Incandescent lights are very sensitive to small voltage changes, so it can be quite noticeable even if the actual voltage drop is insignificant.

Humming in the breaker panel can be normal. If they did upgrade the panel, the POCO may not have upgraded the drop. They sometimes don't. They'll do it only if it really becomes necessary. Based on your measured voltage drop, it's still not really necessary.
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Old 12-17-2011, 06:01 PM   #6
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Dimming Lights and Possible Neutral Problem


I just cleaned up the original post a bit. The voltage actually did go up on the other phase and down on the load side where the table saw is connected to. Is there any reason the voltage should go up?

I should mention the house is about 6,000 sq/ft and has two central AC units which I belive are 2.5 ton, a hot tub, a work shop, electric stove, electric dryer, and electric well pump. If all of these are running along with some lights which is very possible it would draw about 200 amps at 240 volts. The closest transformer pole is 150 feet away from the house so I'd guess the 1/0 aluminum run is at least 150 feet.
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Old 12-17-2011, 06:01 PM   #7
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Dimming Lights and Possible Neutral Problem


I’ve been reading through a lot of forums about dimming lights and have been able to narrow it down to what I believe is a bad neutral from the POCO but wanted to see what you guys think. The POCO says everything is within specs though. They have been out 4-5 times and the last guy that came out twice specializes in the hard to find problems. Below is some info and details I’ve found. When I turn on something with a larger load my voltage goes up on phase. See below for specs.
We have been in the house for about a year and have this issue since day one.
House was built in 1982 and added onto in 2006.
200 Amp service with 1/0 90C aluminum wire (neutral is smaller) underground feed (this seems small for 200 amp service?) I have 3/0 copper going from the meter to the breaker box. 1/0 kinda small. Utility not under NEC
The breaker box and breakers are new and all lugs have been tightened.
Neighbors don’t seem to have any problems.
When I run the vacuum, laser printer tools, AC, etc the lights in the entire house briefly dim. I checked to see what kind of voltage drops I was getting. Using a digital Fluke meter I ran voltage test as the breaker panel and meter box. I get the same voltage changes before and after the meter and breaker panel.
For the test I used a 120 Volt table saw which per my amp meter draws about 14 amps running and during startup the peak is 78 amps. Each phase was using about 10 amps from other appliance etc.
No big load 241 volts With open neutral no change in 240 V will occur.
Start the table saw it drops to 239 volts Thats normal
While table saw is running 241 volts

One phase: Yellow
No big load 120 volts Do you have the 120 and 125 reversed?
Start the table saw it drops to 125 volts
While table saw is running 121 volts

Other phase: Blue
No big load 121 volts
Start the table saw it drops to 112 volts Thats a bit lower than normal
While table saw is running 120 volts
The POCO had a meter on the house for a number of days but they said everything looked good. They did find a source which was drawing 20 amps constantly every 10 minutes which I tracked down to be a bad attic fan.
From what I’ve read I should not see one phase go up in voltage, right?
What else am I missing or should I check? Ground?
Assuming it’s pointing towards a bad neutral with the POCO how can I prove to them the problem is with them.

Try this method. With you at the panel in the house, have you wife plug in an iron. Check the voltage 120 v both legs. If there is an open neutral you
will see the voltage go up on one leg and down on the other. Turn of all electronics. If it does go up, remove the iron imediatley. You have a neutral problem if this happens.Many time the voltage drop is due to a small size transformer. Are your neighbors on the same transformer? If you do see a large VD then it is the utility's problem. If the transformer is 150 ft away that is more than likely the problem. You should still do the iron test.

Last edited by wareagle; 12-17-2011 at 06:14 PM.
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Old 12-17-2011, 06:04 PM   #8
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Dimming Lights and Possible Neutral Problem


Quote:
Originally Posted by Julius793 View Post
Well the poco is known to use the same wire for 100 and 200 amp services (in my area at least). Now I've heard once for a senior electrician that If there is real good grounding system in place it will reduce the dimming when big appliances start up. I can't explain why that would be or if it's true, just figured I would put it out there
That is not true. Has nothing to do with the electrical system.
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Old 12-17-2011, 06:13 PM   #9
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Dimming Lights and Possible Neutral Problem


[quote=BigGuy01;796011]You don't have enough power to run what you're running.

That dimming of the lights, etc. means you have too many electronics/powered devices on. your house can't supply that much power. Consider upgrading your homes power unit(s). As far as size of aluminum cable, for your main feed into your home, it should be a #6. (6 AWG) He haS 1/0. Do you want him to go smaller?

See how many amps is pumping into your home, vs how many amps you're using.

Checking electrical devices, you should have nothing that exceeds 5,000 amps, and that would be your water heater or oven. Or you have one insane table saw. I would hope not.

Checking how many amps your circuit is rated will go a long way. As previously stated, you have too many electronics running for your home to power. Consider upgrading. or using less power. He is already at 200 amps. How big does he have to go?

Any devices that just state voltage instead of amperage, you can find the amperage via Wattage divided by Volts, or Volts divided by Resistance (Ohms)

Also, can't remember what it's called, but there is a plug-in you can purchase from home depot with three lights built into it, use it and plug it into all of your outlets, and determine which ones are wired in reverse, have no grounds, etc. etc. etc. There will be a legend on it that states which lights will light up to indicate what with each individual outlet in your home. If it's bad neutral wiring in any recepticles that will find it.

Also, regarding the lights etc. briefly dimming, sometimes that's just because of the surge of power a vacuum, tablesaw, etc. needs to start running, and the homes circuit is adjusting to that. It's very, very common.
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Old 12-18-2011, 12:24 AM   #10
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Dimming Lights and Possible Neutral Problem


I just ran the iron test. It's late so most lights and electronics were off but a few were on including some lights. I can re-try the test tomorrow with nothing on too. When I plugged in the iron the volage dropped 1 volt on the load leg and it went up 1 volt on the other leg. The iron draws about 12 amps when I tested it with a amp meter. Would this mean I have an open neutral or is a 1 volt increase on the non load side to be expected?

I'm not sure which transformer the neighbors are on or even which one I'm on since most of the lines are burried. If I call the POCO will they tell me?

Last edited by carfan87; 12-18-2011 at 12:40 AM.
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Old 12-18-2011, 01:44 AM   #11
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Dimming Lights and Possible Neutral Problem


On a split supply a sudden drop in voltage on one side
will cause the other side to rise slightly to compensate.
Your voltage drops are not too great,
But are probably due to a lack of power
on the primary side of your utility tranny.
Could well be within there specs but.
If your panel capacity is adequate
and all connections are good theres not much
more you can do.
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Old 12-18-2011, 03:25 AM   #12
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Dimming Lights and Possible Neutral Problem


Quote:
Originally Posted by BigGuy01 View Post
You don't have enough power to run what you're running.

That dimming of the lights, etc. means you have too many electronics/powered devices on. your house can't supply that much power. Consider upgrading your homes power unit(s). As far as size of aluminum cable, for your main feed into your home, it should be a #6. (6 AWG)
There is no way a #6 should be supplying a house with a 200 amp service.

Sorry, BigGuy, but a lot of stuff you have posted here is not even close to code.
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Old 12-18-2011, 08:48 AM   #13
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Dimming Lights and Possible Neutral Problem


Is using 1/0 aluminum code for a 200 amp panel? The inspector still needs to sign off on the main panel replacement (it replaced a 200 amp panel) and wondering if the inspector will even sign off on the POCO using 1/0 aluminum for my main feed?

When starting the tablesaw the non load leg went up 5 volts. Is that considered normal then?
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Old 12-18-2011, 08:56 AM   #14
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Dimming Lights and Possible Neutral Problem


The power company sizes their wiring using a different set of rules, not the NEC.
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Old 12-18-2011, 09:01 AM   #15
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Dimming Lights and Possible Neutral Problem


Everything you are describing is pointing to a neutral issue. There should be no rise on the opposite leg. Did all the neutral connections get checked? The transformer? Weather head? meter base? panel? Have you checked the ground for current?

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