Lights wink ....

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1793

1793

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Location
Louisville, Kentucky
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Inspector
I went to a customer's to investigate the lights, throughout, the house "winking" when motor loads are turned on. The 240V Dryer causes the most noticeable effect. When the Disposer is turned on they "wink" just a bit. Furnace & A/C have the same effect.

The Dryer breaker is located just under the Main, A/C is just below that with the Furnace & Disposer lower in the panel.

Voltage is 125 L1 & L2 to ground. Connections tight, all bonding is in place.

With a load of 25a on one Service conductor the voltage ahead of the Main is 118, with the other at 127.5

Does anyone have any thoughts they would like to share as where check why this is happening to this extent.

I may not be explaining this very well but I hope someone can catch the drift.

Thanks
 
1793 said:
I went to a customer's to investigate the lights, throughout, the house "winking" when motor loads are turned on. The 240V Dryer causes the most noticeable effect. When the Disposer is turned on they "wink" just a bit. Furnace & A/C have the same effect.

The Dryer breaker is located just under the Main, A/C is just below that with the Furnace & Disposer lower in the panel.

Voltage is 125 L1 & L2 to ground. Connections tight, all bonding is in place.

With a load of 25a on one Service conductor the voltage ahead of the Main is 118, with the other at 127.5

Does anyone have any thoughts they would like to share as where check why this is happening to this extent.

I may not be explaining this very well but I hope someone can catch the drift.

Thanks
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It sounds like the inrush current for the motor loads is temporarily pulling down the system voltage. Have you tried monitoring the voltage while the loads are switched on, not just at steady state? How far away from the street transformer is the service? What is the size/condition of the triplex back to the transformer?
 
1793 said:
I went to a customer's to investigate the lights, throughout, the house "winking" when motor loads are turned on. The 240V Dryer causes the most noticeable effect. When the Disposer is turned on they "wink" just a bit. Furnace & A/C have the same effect.

The Dryer breaker is located just under the Main, A/C is just below that with the Furnace & Disposer lower in the panel.

Voltage is 125 L1 & L2 to ground. Connections tight, all bonding is in place.

With a load of 25a on one Service conductor the voltage ahead of the Main is 118, with the other at 127.5

Does anyone have any thoughts they would like to share as where check why this is happening to this extent.

I may not be explaining this very well but I hope someone can catch the drift.

Thanks
Click to expand...

All of the symptoms (L1-N-L2 = 125-0-125 with no load and 118-0-127.5 with load) points to a combination of voltage drop in the service wiring (line to line of 250 with no load and 245.5 with load, which would not be all that bad, roughly 2%, if it were the full service load, but is very high for just a 25A load) combined with a high resistance in the neutral conductor back to the POCO transformer secondary (L1-N going down while L2-N goes up).
If this is a 100A service, what you measured would correspond to a voltage drop of somewhere between 18 volts and 28 volts out of 125 between 0A and 100A load. If it is a 200A service, it is a factor of two worse!
Get POCO to check out the service drop and the transformer.

PS: What happens when you put an equal 25A load on both L1 and L2 at the same time, or put a single 25A load from L1 to L2?
 
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GoldDigger said:
All of the symptoms (L1-N-L2 = 125-0-125 with no load and 118-0-127.5 with load) points to a combination of voltage drop in the service wiring (line to line of 250 with no load and 245.5 with load, which would not be all that bad, roughly 2%, if it were the full service load, but is very high for just a 25A load) combined with a high resistance in the neutral conductor back to the POCO transformer secondary (L1-N going down while L2-N goes up). If this is a 100A service, what you measured would correspond to a voltage drop of somewhere between 18 volts and 28 volts out of 125 between 0A and 100A load. If it is a 200A service, it is a factor of two worse!Get POCO to check out the service drop and the transformer.PS: What happens when you put an equal 25A load on both L1 and L2 at the same time, or put a single 25A load from L1 to L2?
Click to expand...
200a 4/0 URD
 
1793 said:
200a 4/0 URD
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One further mature reflection, since your voltage measurements were to "ground" and 1. the bonding jumper will assure that N and ground are verrrry close and 2. the ground electrode resistance is so high, relative to the resistance of the neutral wire, that it can be neglected, you were actually measuring L1 and L2 to N.
Based on that, it looks like the resistance of your neutral service wire is pretty (acceptably?) low compared to the other sources of voltage drop. There does appear to be a VD (delta V) of 2.5V on the neutral with a load of only 25A. Extrapolate that to 200A (unbalanced) and you are still looking at a VD of 20V just on the neutral.
That leaves high resistance in L1 somewhere along the way (wire or connections) or really bad regulation at the POCO transformer secondary. The latter could be the result of a very undersized or defective transformer or a problem on the primary side.

Is this a long service drop or a long primary run in a rural area? Either way, chances are 90% or better it is a POCO problem.
 
ptonsparky said:
Pay attention to the details. When the voltage goes up on one leg and down on the other, that starts to point to neutral problems. Poor connection either end, or faulted underground.
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That only applies when the relative changes in voltage under load between L1-N and between L2-N is large compared to the change in measured L1-L2 for the same load test. The closer delta L1 is to delta L2, the more certain you are that there is a neutral problem.

If all three service conductors have the same resistance and everything else is ideal, then the change in N (relative to the neutral at the transformer secondary) should be the same as, but opposite to, the change in L1. Together, each will contribute 1/2 of the VD seen by the load.

The OP's measurements (not using a remote ground) are in this general ballpark.
 
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Do the lights get bright bright in part of the house and dim in others as the load cycles? Do you have access to both ends of lateral? Check the voltage at both ends. What are the distances involved? Typical for this area would be a 2/0 neutral.

GoldDigger is right that an open neutral connection will manifest itself with an equal change in voltage. A drop of 7 volts on L1 would give an equal rise of 7 volts on L2. You may have a transformer that is two small, a poor line connection, a ground fault on any or all of the conductors, or just to dangfarfromthe transformer.
 
The few times I've seen this it's always turned out to be the poco xfrmr.
 
mgookin said:
The few times I've seen this it's always turned out to be the poco xfrmr.
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I had a similar issue in a c 1929 home I owned with a 60 amp service (reversible fuse block main disconnect). While the washing machine was running in the kitchen, the lights in the kitchen and bedroom would pulse in time to the agitator motor. One panel upgrade and circuit separation later, no issues.
 
I looked for the transformer feeding this property, underground, and I think I found the correct one, it is about 100' from the House. I'm going to call the POCO today to see if I can meet with someone to look this over.
 
Maybe 25 years ago I was called out on a side job with something similar. The air conditioner caused the lights to blink. I didn't have any test equipment except my Wiggy. I checked to make sure things were tight in the panel and had the guy call the POCO. Turns out his transformer was down the street farther than it should have been. They set a transformer on a pole closer to his house and all was well. I still made $25 for my trouble call.
 
Last call like this I found lugs loose on main breaker, evidence of overheating (discolored al, brittle insulation). Changed out main breaker and helped it a lot but lights still dim a little when dryer starts, definetly poco side.
 
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