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clairmo:
I will assume the home has a 120-0-120 service. This means you have a single phase center tapped source with three current carrying conductors. About 1/2 of this home will be connected to one side of the center tap, and the other half to the other side.
Also I will assume that the washer is powered from 120 and not 240.
See if you can identify two different outlets such that one is on one side of center tap and the other is on the other side. I would like to have these on circuits that do not include the washer and any other varying on-off loads. It would be ideal if there were no loads on either of these circuits, but it is most important that if there is a load that it is constant. Roughly these two circuits will allow us to measure the source voltage of the two phases at the main breaker panel and relative to earth ground.
First, assume you do not have a meter. Connect an incandescent lamp to each of these outlets so you can simultaneously watch both lights. Now run the washing machine in its agitating cycle.
1. Do both lights dim together? If so I might assume a pole transformer primary problem. Highly unlikely. However, there might be a very small effect on one side due to the transformer primary impedance that is common to both secondaries. What I am really referring to here is that both have simultaneous and equal dimming.
2. Does one light dim and the other not change? A high resistance between the pole transformer hot wire on one phase and the breaker box bus bar for that phase. And this is the phase to which the washer is connected.
3. Does one light dim and the other get brighter? If so there is a high resistance in the neutral between the pole transformer and the breaker panel neutral bus bar.
You can do the same tests with a pair of meters, but the lights may actually be better.
You can use a meter to monitor the voltage of the neutral relative to the service grounding electrode. Also monitoring the voltage at the outlet the washing machine is plugged into during this agitating part of the cycle would be useful.
If we assume that the flickering lights are not on the washing machine circuit, that in the past they did not flicker, and that means there has been a change, then my guess is that a high resistance has developed between the pole transformer and the bus bars in the main panel. See below the idea of maybe they have a new washing machine.
I would also assume that when any significant motor starts that there is a momentary dip in light intensity that is greater than the flickering change.
A couple bits of information. I have a test resistor, 10.6 ohms hot, meaning an electric heater. Measurements at one of my living room outlets --- No load 125.3 V, and then with 11.5 A load 121.4 V. This change produces a noticable change in light intensity. Turning my oven on broil produces a 0.7 V change and the light change is not easily detected. Note: the oven is fed directly from the main panel and the voltage change is a result of the pole transformer internal impedance.
At my main panel the 10.6 ohm load on one phase produces a 1.1 V change on that phase, and 0.1 V change on the other phase. I have very low resistance wires from my pole transformer to the main panel and thus the major change in voltage due to the load is the transformer impedance.
You could see what kind of voltage changes you get from turning on and off your customer's oven. First, on each phase relative to neutral, and second with the meter from hot line to hot line.
I doubt that your customer's washing machine produces anything close to 11.5 A change while running. However, inrush current might be much greater. Then there are some new washing machines that might actually have some large changes in input current because of a electronic control of forward and reverse of a motor instead of some mechanical transmission. Did the washing machine change? You might monitor the washing machine input current during agitation.
Are you still working on this problem? If so, what new information could you provide relative my above comments?
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