Ahhh, this gives me flashbacks to a service upgrade I did in a really old neighborhood!
Old 1920's area here where the original services were 30A 240V a house.. I installed a 200A 240V service as the homeowner was having A/C installed & also wanted one of the fancy glass top electric cooktops... Did the service changeout, no problems.. (Municipal utility area, so the city runs the show from start to finish)
Well, it seems 2 other homes on the same transformer had recently been upgraded also, and had added some serious loads also...
I got a call back out after the H.O. I did the work for had his A/C, cooktop, a range & 2-50A Kilns in his garage... It seems on hot days, things wouldn't work right... I read voltage at the panel & it seemed a little low, but still in operating range (114V/112V) with about 120A load on the new panel. So I phoned the utility to check their system.... He calls me back the next night & says they checked & their voltage was fine. (They didn't check it when much of a load was on) I went out there again that night & had him turn everything on... The streetlights were dimming! I read 109V/111V.
This also amused his neighbor behind him who ran some kind of internet server deal.. The voltage fluxuations kept booting his computers into kaos...
After some time yaking with a utility planner I talked him into meeting me out at the H.O.'s house... Turned out a 25KVA transformer was running about 12 houses & had been on the pole since 1919. 2 75KVA transformers banked & some beefier secondaries throughout later.. Everythings fine!
-Randy