As a home owner, I have an ongoing issue which is that everytime any motor kicks on (refrigerator, AC condenser, sabre saw, etc.) the lights dim for a second or two. The main service is at the detached garage and is properly bonded and attached to a grounding rod. This panel feeds the sub panel which is located in the house about 50' away. This sub panel is also bonded and attached to both a grounding rod and cold water pipe. I questioned the electrician about this and he said that it was required by code since they are 2 different buildings. BTW, the work was inspected. Is this accurate? Is this why I'm experiencing the temporary voltage dips, or is there another possibility? Much thanks.

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    How many amps is your incoming service? This could be a few different things, some of them relatively benign, others rather problematic. Also, how many wires are in the feeder to the house from the garage? – ThreePhaseEel Oct 7 '20 at 1:51
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    Does the subpanel have a neutral-ground bond also, or is N and G separate? You know North American/JP power comes in 2 separate "poles" of 120V totalling 240V... what is the voltage on the 2 different poles? Are they solidly within 1-2 volts of each other, or do they spread out sometimes when a big load is on one pole? – Harper - Reinstate Monica Oct 7 '20 at 4:02
  • How far is the main panel from the transformer? And did you put a meter on it to see how much of a voltage dip you have? And what type of lights? Many LEDs are notoriously sensitive to voltage variations. – George Anderson Oct 7 '20 at 15:54
  • 50’ is not that far but the size of the sub panel and the brand of the main panel would be where I would look. A single family home should be on a 100 amp feeder and that it is fed from a main panel that usually means a snap in circuit breaker. I have found many times when large loads have dimming on multiple circuits it to be connections at the main panel causing a dip during the peak load (when the motor spins up) 2 specific brands of breakers/ panels that are notorious for problems are FPE stablock (federal pacific) and Zinsco if your main panel is ether one of these read up on them. – Ed Beal Oct 7 '20 at 21:51

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