5

I'm having an issue with flickering LEDs, the PoCo came out and upgraded my service with a brand new transformer and wiring, they did a power survey before and after and said their side is good now. Previously, they noticed some voltage fluctuations, low voltage, given my distance from the previous tranformer. This was definitely fixed as noted by 120 volts consistently inside the house after their upgrade.

Anyway, flickering issue has been reduced (it's house wide, occurs at the same time for all light circuits, suggesting neutral issue) but it still exists. I can make the flickering occur on demand now by plugging a Keurig into a GFCI beside the kitchen sink and turning it on to pre-heat.

It was during this flicker testing that I noticed a few remarkable things:

  1. When I turn on the microwave (on A leg in the panel) I noticed a voltage drop on A leg from 120.5 to ~118, very reasonable and expected, HOWEVER, I am noticing a voltage increase from 120.5 to ~121.2 on B leg throughout the house. The expectation would be that the B leg does not increase in voltage.
  2. I turned off the light circuit upstairs to check for a loose connection (I tested every single lightswitch for loose neutrals mind you), however, the circuit was still hot. I had to turn off an adjacent breaker for the same room's outlets in order to make the circuit safe to work on. Turning off the outlet breaker does not stop the lights from working and turning off the lightswitch does not stop the outlets working.
  3. Switching the lights to be exclusively on B leg made the flickering worse than switching them over exclusively to A leg, flickering still exists, but it's more faint.

I believe #1 and #2 above are related/causing my flickering issue, I believe the flickering issue to be a tell of a loose neutral or something along those lines.

Unfortunately electricians to date have not given a lot of confidence, but, I'm not sure they found the same findings I have now. I've had 5 visits and no success on fixing the flickering.

I have checked all neutrals on the panel, they are tight, as I said before the PoCo checked their side very thoroughly. How can I begin to diagnose this? Could it be a loose neutral anywhere on the A leg, as in, in any junction box for switches or lights? I don't mind checking them all if that helps! I've spent 100 hours on this, another 20 hours is nothing.

TL;DR - With microwave on A leg drops from 120.5V-118V, but B leg increase by .7 volts from 120.5V - 121.2V. Seeing flickering in the house and noticed an unsafe junction box after turning off the correct breaker for said box. Is there a bigger neutral issue?

Thank you!

2 Answers 2

5

The flaming "burn your house down" emergency is the flickering!

Barring cheap LEDs or bad LED/dimmer matches, flickering is caused by the wires being connected and disconnected rapidly. You can create flickering by plugging in a (preferably incandescent to avoid delayed startup on LED/CFL) lamp into a socket, but floating the plug halfway in, so it just barely starts to make contact, and then vibrating the plug like mad. So you're making the lamp flicker on and off for like five minutes straight. Please go actually do that (or take my word on it).

OK, now yank out the plug and feel it. I bet it's warmer than normal. See all that booger-snot of metal damage that's on the tips of the prongs? Yeah. That is the calling card of "arc damage". Damaged contacts and violent quantities of heat. And the damaged contacts tend to produce worse contact and more arcing, so it's a death spiral in that sense.

We dislike both of those, but what spooks us is the heat. That heat can start a fire - even in a current-limited case like a series arc. (where the issue is a loose connection and loop current is limited to what the load will draw - still plenty enough to start a fire).

This sucker has nothing to do with the voltage drop, and you need to find it.

It sounds like you have considerably more skills than the average bear in identifying circuits and current flow paths generally, so I'd put those to full use in narrowing down the possible locations. I wouldn't make a habit of provoking it until you are sure it's outside your house, nor would I intentionally let it go nuts for testing. But for what it's worth, the enclosure where it's happening will be warmer than it ought to be. (By a detectable amount? Don't know.)

Find it and kill it with fire, before it kills you with fire.

Why lost neutral is a red herring.

The voltage drop you are seeing is explainable. Consider you are dealing with five voltage drops:

  • A) Phase L1, from panel to microwave
  • B) Neutral, from panel to microwave
  • C) Phase L1, transformer to panel
  • D) Neutral, transformer to panel
  • E) Line and neutral of the utility's distribution wires back to the power plant.

E is undiscernable, and probably trivially small since they are distributing 9600V on at least #4AL wire. Assuming normal installations, A and B will be equal. If we assume hot and neutral service drop wires are of equal size, C and D will be equal.

Obviously, the microwave sees all four voltage drops. So

A + B + C + D = ~2.6 volts.

However a quiescent circuit on phase L1 sees the last three voltage drops.

And here's the rub: A circuit on phase L2 sees the "D" voltage drop as an anti-voltage-drop. Because neutral is being dropped farther away from it. That is, the "D" drop causes L1-N voltage to drop and N-L2 to rise by the same amount. So we know D = 0.7 volts.

Let's assume the power company dropped the same size neutral as hots, so C = 0.7 volts.

A + B + 0.7 + 0.7 = 2.6 volts.

A + B = 1.2 volts.

A = 0.6 volts.
B = 0.6 volts.
C = 0.7 volts.
D = 0.7 volts.

These are normal values, my friend.

2
  • great answer, I appreciate that the voltage drop is normal, what about the increase? Others say 0.5V increase in B leg is probably capacitive coupling. As for the flickering, it's stopped after I've removed the Keurig, it was running every minute keeping the water hot. The flickering was happening at the exact same frequency, unplugged it, no more. I tested the circuit, it only had the one outlet on it, and the neutral resistance was negligible on my multimeter. I believe everything is good except the voltage increases. Thank you!
    – AutoM8R
    Commented Feb 7, 2022 at 4:12
  • @AutoM8R I explained voltage rise on L2 at "And here's the rub" but I've expanded. Of course flickering stops when current draw is reduced to almost nothing! LOL! Keurigs pull like 12-15 amps and the LED is 0.2 amps tops. What does the Keurig and the flashing lights have in common? Does an incandescent light plugged into the Keurig's socket also flicker? Commented Feb 7, 2022 at 6:02
0

LED light bulbs work differently from incandescent. Inside each "bulb" which technically should be called a lamp is an LED which works on Direct Current and a circuit that has a rectifier to convert AC to DC. The LED itself has a Vf- the voltage at which electricity goes forward. Below that Vf- no light. Above that Vf- light. So the flicker happens when the voltage delivered to the LED drops below the Vf. In bicycle light design where there is a dynamo delivering AC, but in an uneven fashion based on wheel speed, it is normal to include capacitors in the circuit board of the light to smooth out the flow and to maintain light when the bike stops for a minute or two on the road. Home light bulbs don't have the capacitor thing down sufficiently to handle voltage fluctuations. We had a similar flickering issue with a Fellow brand hot water pot. It has a temperature maintenance cycle. While neither the microwave, nor the countertop convection oven cause light flicker drawing comparable amps, the hot water pot causes flicker and the flicker only happens when maintaining temperature. The hot water pot does not cause flicker in the initial heating process.

1
  • 1
    Welcome to Home Improvement, please take the tour. I'm sure there's something resembling an answer in here, but without any formatting, it's hard to read and suss out what the answer actually is. Please edit your answer to directly address the question in a clear and concise fashion. Background info is fine, just make sure that the answer is easy to find.
    – FreeMan
    Commented Feb 14 at 3:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.