Lights and appliances flickering with Federal Pacific Panel

[patricknola]

Hey Guys, I have a customer who is having a problem with flickering lights and a fan whose speed fluctuates up and down. I've already gone by the residence and checked voltage at the main breaker and then checked voltage at every breaker.The lights only flickered for a brief moment while i was there and as far as I could tell voltage remained constant (116v). As I said this is a Federal Pacific panel and sometime in the past there was some re-wire/upgrade where copper wire was intermingled with aluminum wire.The customer is telling me that lights are flickering in the bathroom, in the kitchen and in the living room where there is also a fan whose speed fluctuates up and down when the flickering happens. This apt. is in a big building and when I went by I didn't have access to the mechanical room where the meter was located. I called the local energy provider(Entergy) and had them come out to check voltage at the meter. My next step is to start checking light switches, taps in fixtures and light bulb socket. Any ideas?

 

[growler]

The customer is telling me that lights are flickering in the bathroom, in the kitchen and in the living room where there is also a fan whose speed fluctuates up and down when the flickering happens.

Are these lights all on the same circuit? If so you may have a bad breaker (arcing at stab-lock).

 

[gar]

191016-0839 EDT

partricknola:

You absolutely have a voltage variation problem. When a fan changes speed you have a serious problem and it is not just a one cycle problem.

Use two 15 W well frosted light bulbs as voltage testers, one on each phase. Use the bulbs to check voltage on the main panel bus bars. If one light gets bright, and the other dim, then there is a neutral problem before the main panel. If both dim then likely a problem before the panel, or with main circuit protection, or connections in this area.

If the main panel buses look ok, then leave one light on one phase, and use the other light to check the breaker outputs of the breakers on the opposite phase. Then reverse the test. If these are all good, then connect one light to an extension cord, and go see what circuits show variations. And where in the circuits.

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[gar]

191016-1353 EDT

To continue.

Assume a stiff center tapped pole transformer as the power source. This means we assume the voltage at the transformer on both phases is constant independent of any loading. At my home this is approximately correct, a 50 kVA pole transformer.

At my main panel bus bars I get the following approximate results: The load being applied is about 10 A from a 1500 W 120 V space heated. The loaded phase drops 1 V and the unloaded increases 0.4 V. Note loaded and unloaded only relate to the changing load. It does not matter whether other loads exist or not, just that they don't change while doing this test.

We expect this approximate 2 to 1 ratio between the two changes. You can study such a circuit on paper and see why.

If your two circuits don't share the same common wire (you may call this neutral) the entire length, then the voltage ratio will be larger. In another location this 10 A loaded voltage change is 2.4 V, but that won't change the above 0.4 V by very much.

A 1/3 HP 120 V inexpensive induction motor has a starting current of about 25 A RMS with no mechanical load with a duration of about 6 cycles.

Incandescent bulbs are relatively good qualitative voltmeters when looking for voltage changes and comparing different circuits.

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