Dimming lights

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keith gigabyte

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New Kensington, Pa
So we just replaced a service on a customers home. 2 days later call that when they run the washer the lights dim and go bright on agitate cycle. I’m thinking some loose connection or miswire on branch circuit. Just getting my brain in gear for tommorow.
really concerned because they said no problems before we installed service
 
180718-2111 EDT

keith gigabyte:

Some key points.

1. You were told there was no major light flickering before the work you did was done. If true, might be suspect, then most likely some connection you made that is common to the washer, or something you did not do but but was affected by some wires you may have moved somewhat is where to look for a bad connection.

2. What is flicker? I can see an incandescent flicker with as little as 2 % change in voltage, but I have to be looking closely, sort of know when to look. From peripheral vision I probably would not notice. I would expect more like 5 to 10 % change for an average customer to detect flicker. At 120 V this is in the range of 6 to 12 V change at the bulb.

You need to make measurements.

What exactly did you replace?

You need a good meter with a resolution of 0.1 V on a range that reads 120 V. You may need something with fast response. However, if you use a 1500 W space heater to provide a load change from 0 to about 10 A, then you can control the on-off timing.

Two 7.5 W incandescent bulbs also can be useful as qualitative voltage detectors, one on each phase.

Measure voltage change directly on the wires, not the terminating lug, at the inpit to the main breaker. Do line to line, each line to neutral, and neutral to a screwdriver in outside earth. If large changes occur, then there is at least a problem before the main breaker.

Do the same tests on the panel bus bars.

If everything is good at this point, then move on to the washer branch circuit and anything common to it.

.
 
I have seen this before and found the problem was associated with the GEC connection. Someone hit the ground rod acorn probably with the lawnmower and broke the conductor. On another occasion the utility connection outside (under ground transformer) for one particular house had a bad phase connection. Found it by checking the incoming line voltage at the panel when the well pump started. Just a thought.
 
dec said:
I have seen this before and found the problem was associated with the GEC connection. Someone hit the ground rod acorn probably with the lawnmower and broke the conductor.
Click to expand...

There is no way that a compromised GEC can make the lights dim.
 
180719-1156 EDT

The original post is quite unclear.

What does the word "lights" mean? Is it just one light, or multiple lights on different or the same circuit? If multiple lights, then simultaneously how do the intensities change?

If one light dims, and at the same time another light brightens, then there is somewhere a common neutral problem.

If one light dims, and another light does not change much, then it is likely a common hot line problem problem.

.
 
retirede said:
Could definitely be a neutral issue. But that still has nothing to do with the GEC.
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Right. How can a conductor that is carrying no current affect the voltage on the energized conductors? It can't.
 
gar said:
180719-1156 EDT

The original post is quite unclear.

What does the word "lights" mean? Is it just one light, or multiple lights on different or the same circuit? .
Click to expand...

It's always better just to visit the home and see what's happening for yourself. Half the time what the customers gives you as symptoms over the phone are useless.

If the lights are dimming and brightening it's enough so you can see if it on the line or load side of the main breaker.

It's always possible that some termination didn't get properly tightened during a service change, that's why you have to be methodical.
 
keith gigabyte said:
So we just replaced a service on a customers home. 2 days later call that when they run the washer the lights dim and go bright on agitate cycle. I’m thinking some loose connection or miswire on branch circuit. Just getting my brain in gear for tommorow.
really concerned because they said no problems before we installed service
Click to expand...

I have serviced this exact complaint (lighting that dims and brightens while washer is agitating) several times and even had it happen in one of my own homes years ago. In every instance it was a service neutral failure. Some on PoCo's side up at the pole, some where the drop hits the house, and in the one on my house, it was an UG service that pulled down as the improperly compacted soil backfill settled, pulling the neutral off its lug in the meter base.

i would take the customer's insistence that this only started since you guys worked there with a grain of salt. Could be true, could be a lie, could be they never paid attention to the lights while the washer was running.h
 
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