Dimming complaints

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kwired

Electron manager
Location
NE Nebraska
Do if I hook up to the power co ground rod I put my other test lead on one phase is wat you are saying then I should have the correct voltage

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Unless you have access to transformer secondary terminals to connect test leads there, you are somewhat limited to only testing for voltage drop on the grounded neutral conductor.

One other problem you can have though connecting to the electrode at/near the transformer helps eliminate it, is measuring voltage that is actally drop from the primary distribution voltage system - since it's grounded conductor and the secondary grounded conductor are bonded together at the transformer they are essentially the same conductor any voltage rise on one is also a voltage rise on the other.
 

nickelec

Senior Member
Location
US
Im going to go out there tomorrow but I'm pretty sure there are no Transformers I can hook up to its all underground service there are no over head lines at all there transformer are usually under ground as well

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growler

Senior Member
Location
Atlanta,GA
I just spoke to one of my guys that was out there he was telling me he was getting fluctuating voltages from 112--118 phase to neutral, it was a hot day yesterday also so neighboring loads would/could make it dip even lower .

That doesn't give much information.

What was the voltage reading from phase A to phase B ?

voltage from A to neutral ?

voltage from B to neutral ?

Last, where was he taking the voltage measurements ?
 

nickelec

Senior Member
Location
US
I'm not sure exactly I will be heading out there tomorrow my self and will update

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
190715-1031 EDT

nickelec:

What I am suggesting is go to the pole transformer pole, and you will find a wire coming down the pole that attaches to a ground rod at the pole. This is the rod I am referring to. Usually this grounding wire is covered by wood near ground level and it may not be easy to directly connect to the rod. A screwdriver poked in close to the rod will pretty well get the voltage of the rod.

The same applies to a pad mount transformer, but I don't know where the earthing connection is made, and/or if the pad may be the connection. A screwdriver close to the pad should be sufficient.

Normally there should be very little current to this pole transformer ground rod. Possibly less than a few amps. Thus, voltage drop from the transformer center tap to your screwdriver or connection should be small.

Your other meter lead gets connected to the neutral bus in the main panel. The voltage reading should be small, and a 10 A 120 V load should not produce much change. I am hoping for less than 1 V. If you see more than a change, either up or down, of 2 V or more, then I would suggest a neutral problem. I don't even like the 2 V criteria, but we have no information about your supply lines.

Without you adding a load if the voltage drop of the neutral is substantial, over 1 V, and there is no likely large load in the home, then it may indicate a neutral problem.

Values to use as a criteria depend on your experience, and what you see at the site.

..



 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
190715-1107 EDT

nickelec:

If everything is underground, and if you know where the transformer is, then poke the screwdriver in close to the transformer.

Since we have this complication, then it is possibly better to just try to use measurements at the input to the main panel. Try to put the voltmeter probes directly on the input wires. You need to have the ability to separately load each 120 V phase, and 240 phase to phase. Two 1500 W heaters will give you this capability.

Two voltmeters would be useful, but not necessary. The meter probes are to be directly on the incoming lines.

1. Read the phase A to neutral voltage change with a 10 A 120 V load added to phase A.

2. Same load change, but read the phase B to neutral change.

3. Same as 1, but now do it on phase B.

4. Same as 2, but load change on phase B, and voltage change on A to neutral.

5. Next is a 240 V loading. I would like to do a 240 V 10 A load change without any connection to neutral, but that is harder to do than just than just plugging in the two heaters.

6. Measure the phase A to phase B voltage, and each phase to neutral.

7. Load each phase to neutral simultaneously with a heater. We assume each heater is the same resistance, or at least close. Read the voltages of 6 again. This test should produce little change in the neutral current.

From the above measurements we should be able to learn more. Unfortunately there may be load changes from neighbors, or within the home being tested that interfere with the measurements you are making. You sort of need to make judgements on the data to filter out some of this unwanted noise to your experiment.

.
 

nickelec

Senior Member
Location
US
So I jsut left the customer and measured voltages
Phase a to neutral 105
Phase b to neutral 118
Phase to phase 116

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
190718-1625 EDT

nickelec:

The voltage readings you took are next to useless in trying to determine the cause of your light dimming problem.

Phase to phase should be 118 + 105 = 223. The 105 seems low in comparison to the 118, but that simply could be high loading on that phase.

..
 

kwired

Electron manager
Location
NE Nebraska
So I jsut left the customer and measured voltages
Phase a to neutral 105
Phase b to neutral 118
Phase to phase 116

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Something not right with those numbers, is this 120/240 single phase or 208/120 three phase source for this?

208 system could read as high as 216 fairly easily phase to phase, but probably will read less if you are dragging one phase to neutral down to 105.

Still might be possibility of bad neutral I guess, especially if a 208/120 system. I don't see single phase 120/240 having those values, as said line to line volts should add up to 223 in that case.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
190718-2313 EDT

nickelec:

Your measurements after correction do not correlate with a a center tapped single phase transformer with mostly resistive loading, and no major source series inductance.

With whatever present loading is on my home I read 122.7, 122.0, and 244.7 . It is just luck that I didn't see a tenth or two difference in the sum. These measurements are with one meter, and power system voltage jumps around a little over short times.

.
 
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