211022-0834 EDT
Buster2021:
You have had good responses from persons that have some reasonable understanding of electrical circuit theory, and troubleshooting.. This type of problem has come up way too many times on this forum. What I don't understand is why so many average electricians don't understand basic electrical circuit theory, and be able to troubleshoot such problems. I also don't understand why the problem ( poor electrical connection ) seems to be more related to the neutral, and is seldom mentioned relative the hot wires.
When you have flickering lights or other indications of a high resistance problem, then troubleshooting should start at the main panel. Measured results are somewhat different on a systems using two phases of a three phase system compared to two phases of a center tapped secondary of a single phase source system. The single phase sourced system I will comment on.
The power company single phase transformer has one primary winding, and a center tapped secondary. At the power company transformer location the center tapped secondary will be grounded with a local ground rod at that point. Resistance to earth unlikely to be less than 1 ohm, and in my area about 10 to 20 ohms, and some areas much higher. The ground rod at the main service entry point will be approximately the same resistance. At my home the ground at the home is much lower because it is about 150 ft of 1.25" diameter copper pipe.
The service drop from the power company transformer to the main panel is only three wires, two hots, and one neutral. I will assume that each of those wires has the same diameter, material, and thus each is equal in resistance to the others. The only impedance difference between each of the these three paths is transformer internal impedance of each of the hot paths, and meter impedance of the two hot paths. For simplicity I will assume these added impedances are small compared to the wire impedances.
Whenever you see voltage variation in a facility ( lights flickering, or motor speeds ( especially fans ) varying ), then it is my opinion you start by looking at the voltage variation at the main panel. I like to use an approximate 12 A 120 V load ( a small space heater with fan, I don't like the fan, but that is how you get high power in a small space ). Because my daughter has my small, only working one, 1500 W heater I am using a 1000 W hot plate as my test load.
I want the first main panel voltage measurements to be between the actual power wire to the neutral bar, not the bar itself, and the actual hot wires from the meter to the panel, again actually on the wire. This eliminates from the measurements any voltage drops at those termination points, and it provides you with the closest measurement of the voltages at the meter outputs.
My measurements at the main panel location with a 1000 W load are:
Unloaded side line to neutral 124.4 to 124.6 an 0.2 V positive change, in other words the neutral drop with 8.1 A change.
Loaded side line to neutral 123.6 to 123.1 an 0.5 V drop. Thus, 0.5 -0.2 = 0.3 negative change in voltage in the hot wire. And this side has about 0,2 V additional voltage drop from the transformer winding and meter coil impedances.
These voltage drops result from approximate impedances of 0.2/8.1 = 0.025 ohms for the neutral, and 0.3/8.1 = 0.037 ohms for the hot path. If we had a one side with 100 A load, then the voltage on that side might be dropped from 123.6 to 117.4 or 6.2 V.
In most homes I expect you will see somewhat greater drops for these loads. From what your measurements are you will have to decide whether to call the power company or not.
For internal problems in a home you use the same kind of test and make judgments based on the results.
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. Our local POCO folks have been instructed not to verify any problems on their end from a liability standpoint.
