alabama1984

Hi, Turns one of the contacts in the knife switch mechanism was a bit corroded and arching. Since this is a Canadian installation, I’m not sure how relevant American codes are. In any case, the wires split off after about 30 cm. (I always thought each 120v leg was one phase off from the other, which is why they could be combined to give 240v. But then that all comes from one 25kv line... anyway, sorry if I used the wrong terminology!) Happy Christmas everyone!

Yes, I am very sure – the buzzing is louder on fuse box than on the transformer enclosure. It is a fairly modern (1987) two-phase system. The HVAC setup is two triple-split heat pumps each with three stages of 5kw auxiliary resistance heat.

The two breaker boxes are each rated at 200 amps while the main is fitted with 300 amp bolted fuses. The switch on the right contains a spring-action knife switch and the 300 amp fuses. The centre enclosure has within it the transformer for the meter (which is located outdoors). To clarify, the breakers aren’t buzzing, it is the fuse box on the right which is making the noise when under heavy load. And yes, this is a house.

With six stages of electric heat turned on (totalling 30 kw) the separate 400 amp main produces a loud buzzing and vibration. Is this normal? Image Insert: 154.83 KB Image Insert: 162.64 KB Image Insert: 189.33 KB