Dimming complaints

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nickelec

Senior Member
Location
US
So I have a customer who we did a job for the exsiting set up was

3 meters 3 disconnects 3 sub panels
New set up is the same except they wanted to convert two to meters so we did the work she had told me that the lights would dim some times. Before we did the work .

We did the work and now naturally the dimming got worse. (Of course)

Keep in mind this is an old con Ed loop service that probably feeds 4-5 house maybe 6

Besides loose neutral connections bad grounding what else should I look for to help them out is there any way I can test if the neighbors loads are causing the dimming

My first thought was it's probably there ac but she's telling me the AC was off


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kwired

Electron manager
Location
NE Nebraska
what else might have changed besides meters, loadcenters, and other distribution type items?

Was there remodeling and branch circuit changes, load changes, etc.? Maybe changed from incandescent lamps to LED's and voltage fluctuations show up even more than before in the light output?
 

kwired

Electron manager
Location
NE Nebraska
Would Neighbors loads have an effect?

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It can.

Could be enough load on transformer to draw voltage down, can common conductor that feeds multiple customers and it will have voltage drop involving all the load on it not just the load of your customer, long length feeds only makes things worse in those kind of cases. Average volts may be fine, but somebody's air conditioner starting up may put a temporary drop that effects everyone connected to that source.

Little more extreme cases could have nearby industrial plant that has conditions that draw primary distribution voltage down for even larger area , like while starting a large motor.
 

nickelec

Senior Member
Location
US
Thtas my only assumption at this point voltages are good , gec is solid neutral to ground bonding is all on point I can think of anything else

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nickelec

Senior Member
Location
US
Before and after
51b1324570e8a2acdc9d17668cace287.jpg
22c813e86d0ce9fc686af30861879ed2.jpg


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kwired

Electron manager
Location
NE Nebraska
Grounding and bonding shouldn't really matter when it comes to voltage drop issues.

Length of conductors, impedance of source and amount of loading are things that all will have an impact (presuming there is no bad connections causing issues)

Underground conductors fed from source straight to a house usually has less troubles unless transformer itself is being drug down by loading than a typical transformer in middle of block that supplies nearly every house on the block, often via long runs of somechat marginally sized overhead conductors. That #4 aluminum service drop cable might be able to handle a 100 amp service without overheating, but is going to have much more voltage drop issues when starting motors than a 4/0 aluminum underground lateral or even 1/0 aluminum likely will have.

If the transformer is marginally sized, you have voltage drop before you even consider the VD in the service drop/lateral.
 

nickelec

Senior Member
Location
US
I've had dimming issues before caused by loose neutral connections and/or rotted out enclosures where grounding was compromised but in the case it's most likely VD

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nickelec

Senior Member
Location
US
Also she is telling me that the light get dim s d sometimes brighter that to me would indicate a loose neutral connection

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
190714-2352 EDT

nickelec:

You need a DVM with at least 0.1 V resolution on a range that reads 120 V. Usually called a 3 1/2 digit meter. In some ways a 4 1/2 digit meter is too much resolution. A 1500 W space heater, and possibly an extension cord.

Making measurements in just one main panel may be sufficient, but not, if there are problems in the other panel.

For a minute or so monitor the voltage of one 120 V phase on the wires coming from the meter, and then the other phase. Note the kind and degree of variation on a given phase. Also when no loads are changing in the home quickly measure the voltage on each phase. These two measurements should be quite close.

The change in voltage over a short time, the about 1 minute period will give you a feeling of system changes. At my website http://beta-a2.com/EE-photos.html plot P26 has a resolution of 1 second. At http://beta-a2.com/energy.html plot PE1 you see larger variations.

Next setup so you can switch the 1500 W heater on and off while monitoring the phase voltages in the same locations as before. This heater produces about a 10 A load, roughly 12 when cold. Does not make much difference the where the heater is plugged in.

The phase being loaded should show a voltage drop. While the unloaded phase should show a slight increase. record these values. Then do the same loading the other phase.

From another post of mine
The next next includes everything to the point of origin of the power. Here the change in voltage to the load is measured rather than the voltage drop along some path to the load. The 10 A load change produced a voltage change of 1 V. Note: this includes all the loop impedance. So neutral is an added component. Assume this is 1/2 the loop impedance, but it is actually somewhat less. Doesn't have the main circuit protection, and meter in its path. Using 0.5 V at 10 A as the hot side drop, then 200 A across the 240 (air conditioner load) is a 10 V change to a 120 V light circuit. This change in voltage to a tungsten incandescent bulb probably will be noticed by a person not looking for the flicker.

Most of that measured 1 V drop is not from the 50 kVA pole transformer. This is easily seen by looking at the voltage change of the opposite phase when the 10 A load is applied. Mostly the service drop, meter, and main fuses are the important impedances.
So 10 A change at 120 V at my home produced a 1 V change between my neutral bus and the 120 V bus being loaded. Something less than 0.5 V is on neutral from the transformer to the neutral bar.

Do some measurements and see what happens. Try your own home first.

Yes to your neutral suggestion. This will clearly show up in the measurements I suggested above.

.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
OP and any other: Get and use more than one meter. We used a set of lamps in series for years and Gars past suggestions of low wattage lamps work, but you are charging enough to have meters for VD checks. Buy them. Learn to use them, or quit these types of service calls.

End of rant.
 

growler

Senior Member
Location
Atlanta,GA
We did the work and now naturally the dimming got worse. (Of course)

Also she is telling me that the light get dim s d sometimes brighter that to me would indicate a loose neutral connection

sometimes customers do give correct information but sometimes they don't so it's best not to trust the symptoms provided by customers.

You just have to go to the job site and figure out if the neutral is bad or if it's voltage drop caused by a bad connection.

Just because you did some work and a customer says a problem got worse doesn't make it something that you did ( it could ). Sometimes problems get worse when nothing at all is done. Many times people think that if you work one one part of an electrical system it will repair all problems.

At least half of the bad neutrals I find don't even belong to the homeowner they are power company cables (overhead or underground ).
 

kwired

Electron manager
Location
NE Nebraska
Also she is telling me that the light get dim s d sometimes brighter that to me would indicate a loose neutral connection

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Excessively long and/or undersized supply conductor can look like bad neutral because of voltage drop in an otherwise good condition neutral conductor.

I've had dimming issues before caused by loose neutral connections and/or rotted out enclosures where grounding was compromised but in the case it's most likely VD

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Grounding or lack of it shouldn't matter.

Improper installation that depends on a grounding conductor to carry current can create VD issues if grounding connections are compromised. A proper install doesn't depend on grounding conductors to carry current.

Grounding electrodes can carry current, but the grounded service conductor should still be low enough resistance to carry the entire load whether the electrode is there or not.
 

growler

Senior Member
Location
Atlanta,GA
Excessively long and/or undersized supply conductor can look like bad neutral because of voltage drop in an otherwise good condition neutral conductor.

There is one difference. With voltage drop due to bad connection or undersized conductors you will never see lights get brighter or see a higher than normal voltage on one phase.
 

kwired

Electron manager
Location
NE Nebraska
There is one difference. With voltage drop due to bad connection or undersized conductors you will never see lights get brighter or see a higher than normal voltage on one phase.
Seen it before. Was pretty extreme case of small conductor for length of run, maybe 2000 feet of 2 AWG aluminum 120/240 feeder to a maintenance shed at a golf course.

My first thought was bad neutral. We tried to find faults in that run and one or two of best possibilities we found with a fault locator we did dig up and found nothing. Finally came to conclusion there is just enough VD on the neutral to give similar symptoms of an open neutral. Think about it, if you load one line an neutral hard and have significant VD, the voltage of the unloaded line (or lightly loaded line) is going to go up in relation to neutral. If neutral were actually open and you only ran a single 120 volt load, it wouldn't work at all, we were still able to run a single 120 volt load.
 

nickelec

Senior Member
Location
US
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

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
190715-0957 EDT

All the wires from the power company transformer to the main panel input terminals are likely the same material and size, and thus each has the same resistance. If an overhead line has a steel neutral and not adjusted in size and/or material for resistance, then neutral resistance could be higher. Measurements at my home imply about equal resistances.

The hot path vs the neutral has additional impedance. Some in the transformer, in the meter, and the main breaker or fuse. The main breaker or fuse can be eliminated by making the voltage measurement on the wire at the main panel input. Thus, a slightly lower voltage drop occurs along the neutral path vs the hot path for a 120 load. A 240 V load produces no neutral voltage drop.

If you go to the power company transformer and connect a test lead to the transformer's ground rod, or a screwdriver close to the rod, then you can do a direct measurement of the voltage drop of the power company neutral path to the main panel. But to a great extent you can get a good estimate of the neutral voltage drop by voltage measurements at the main panel input and various loading of 120 V phases, and 240.

.
 

nickelec

Senior Member
Location
US
190715-0957 EDT

All the wires from the power company transformer to the main panel input terminals are likely the same material and size, and thus each has the same resistance. If an overhead line has a steel neutral and not adjusted in size and/or material for resistance, then neutral resistance could be higher. Measurements at my home imply about equal resistances.

The hot path vs the neutral has additional impedance. Some in the transformer, in the meter, and the main breaker or fuse. The main breaker or fuse can be eliminated by making the voltage measurement on the wire at the main panel input. Thus, a slightly lower voltage drop occurs along the neutral path vs the hot path for a 120 load. A 240 V load produces no neutral voltage drop.

If you go to the power company transformer and connect a test lead to the transformer's ground rod, or a screwdriver close to the rod, then you can do a direct measurement of the voltage drop of the power company neutral path to the main panel. But to a great extent you can get a good estimate of the neutral voltage drop by voltage measurements at the main panel input and various loading of 120 V phases, and 240.

.
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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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
190715-1024 EDT

nickelec:

Those are significant voltage changes. But you have to do some correlation with what is happening in the home or elsewhere. That is why you do your own controlled experiments with various loadings, and measurement points.

Ir you personally are not there making measurements, then it may take a long time to solve the problem.

.
 
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