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My garbage disposal was on the same overloaded circuit with many other items in my 1949 home. Lights would flicker when the disposal would come on. These were all on the same circuit.

I recently ran a new circuit for my disposal (had electrician do the panel work). Strange thing is that the lights on the old circuit, that the disposal was on, will still flicker when the disposal comes on.

The age old question, any guesses on what could be causing this flicker when the disposal is on its own circuit? Could it be that a wire is loose on the light's circuit in the panel?

Clarification: They do not flicker but instead dim briefly when the disposal first starts up. Sorry, I used the wrong words.

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  • How many HP is the disposal, and what size is your service? – ThreePhaseEel May 19 '20 at 2:55
  • The panel is 200 and the disposal 1/2HP. – junta May 19 '20 at 3:44
  • Do they flicker, or do they just dim briefly when the disposal starts up? – Carl Witthoft May 19 '20 at 14:31
  • you might have higher resistance between meter and pole than expected, so the load drop the voltage of the whole house. – dandavis May 19 '20 at 16:18
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  1. If the light does flicker also if a hairdryer or vacuum cleaner is connected to the same outlet/box as the garbage disposal, it is likely a problem upstream the location where both circuits (light, garbage disposal) are connected. A loose connection acts as voltage divider in combination with the garbage disposal or any other big load. F.e. backstab connections are known for problems.
  2. If the light does not flicker if the garbage disposal is replaced by a hair dryer or vacuum, it could mean that the garbage disposal motor emits some energy, e.g. HF or inductive surges, that disturb other electronic devices nearby. Maybe the motor capacitor has gone bad or the graphite elements/sliding contacts are worn out.

In both cases the motor should have less power compared to an installation without any problem.

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  • I unplugged the disposal and plugged in a hair dryer. I flicked the outlet switch on and no dimming from any of the lights that were previously dimming. So my understanding is that the disposal itself may be the issue and would mean there isn't an electrical problem to resolve? – junta May 19 '20 at 23:28
  • Yes, the disposal most likely has a fault, if the hair dryer has the same or more nominal Watt then the disposal. – xeeka May 20 '20 at 3:27
  • Just read the last added sentence, it would be ( only) a problem when the motor starts. That could mean there is much residual garbage or any other reason for a high mechanical load when the motor is starting, e.g. a bad bearing. In that case a motor can draw a huge current when switched on causing the voltage to drop. But it could also mean that there is a bad connection in the wiring upstream of both circuits, i.e. there could be 2 problems. – xeeka May 20 '20 at 3:37
  • Testing the lights on the separate circuit that dim, not all of them dim. So it sounds like one thing I should do is just check the wiring in the impacted rooms to see if anything is loose. Two more things to add. There is actually another circuit that the lights dim besides what I just mentioned. This circuit shares the same receptacle as the disposal. The receptacle is half hot and has two different circuits. Not sure if that is worth mentioning. Thanks for the possible explanation of this situation. – junta May 21 '20 at 1:56

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