It can be several things. It is all dependent on the problem.* Too many things on the circuit and it is trying to trip the breaker but the surge is over before it can. in layman's term: It is like trying to stick 10 pounds of crap in a 5 pound box.* The service capacity is too much at the transformer and can not carry the load. In layman's term: It is like the little engine that coundn't.*They have a serious problem with their service neutral. There is potential fire or electrical damage to equipment due to higher the normal voltage. In layman's term: it is like there is potential fire or electrical damage to equipment due to higher the normal voltage.

- Duane Jennings (Grass Valley, CA), 03/25/2017

Just explain to them how a motor takes much more current to start and get up to speed than to run at that speed. Have them think about how little fuel is required to hold 60MPH on the highway. It will be intuitive to them that it takes more when they go from zero to sixty. Then have them consider what it would take from under their hood if their car could even come close to zero to sixty in under three seconds. Then just explain that the huge current draw causes a voltage drop that causes the lights to dim even though they draw little current.Joe

- Jerry Martin (Northport, MI), 03/25/2017

Just tell them the truth- the power company are a bunch of cheapasses and undersize the aerial drop from the powerline transformer to their house, and then when big motors like a heat pump start up, they draw more power than the rest of the house combined for a fraction of a second. So when the big motor on heat pump starts up, the in-rush of current drops the voltage on the line into the house a few volts. It takes surprisingly little voltage drop to make a notible dimming of lights.You can even point out that a typical 5hp motor has inrush of 168A, even if it only draws 20A while it's running. Shoot, if the pole pig is only 25kVA, that in-rush would completely saturate the transformer and dim *everyone's* lights.

- Fred Ward (Pleasant Vale, IL), 03/25/2017