About three weeks ago, my boss's home lost one 'leg' of the incoming 240. Every other 120 circuit in the box was live, every other alternate one dead. No 240 devices in the house worked.
I told him over the phone to throw the main off/on, then take a peek inside to see if there was any sign of heating/arcing where the two legs come into the main.
His main is bolted to the buss bars, and the incoming lines were tight, with plenty of No-Ox on the joints... nothing loose. Cycling the main didn't fix it. He called an electrician.
The pro told him to just wait... it was a power company problem. Sure enough, about two hours later, the dead leg came on, and everything is OK since.
Now... I know only enough about distribution to confuse me about this problem. The transformer on his pole is single-phase in, center-tapped secondary on the output. You CAN'T loose just one leg, unless....
Unless is later; because -- yesterday my son-in-law reported the same problem. This time, I whipped over to his house with a DVM, and checked it out.
Same thing... one dead leg. But the can on his pole is the same single-phase in, center-tapped secondary affair out. HUH? Three hours later, power was restored.
So... unless.... unless there is a thermal breaker of some type internal to the transformer and separate for each leg, as opposed to just shutting down the primary.
Both my boss's and son-in-law's cans have "cricket" disconnect breakers on the primary side.
Does anybody know if a standard residential transformer has thermal breakers on the secondary?
Oh... yeah... metal content. The can is steel. The wiring is copper.