Reply To: Motors and thermal protection

Sven-Olof Jansson

Thanks for coming back Ed!

Clearly I draw too much out of the “formal” definition of DC bias as being [non-random] deviation from the expected mean of a periodic function (I see a sine-wave in front of me: expecting mean to be zero ± random variation, but observing a mean consistently deviating in one direction from the expected). Suppose it goes to show that one should be careful with extrapolating.

Your description on US power is really helpful. Replacing the gas hob in Boston with an electric one, probably wouldn’t be quite as complicated as I imagined; once again found guilty of extrapolation, this time from the Swedish power system, where there is 400V (16 – 24 amp) 3-phase all the way to the residence’s fuses, at which point the fuse will decide what comes out of the socket: 400V 3-phase for appliances like the hob, 220V 3-phase for some heaters, and 220 V single phase for the rest. A ground fault breaker sits at the centre of the net.

Logic – though mine at time falters – seems to say that as there is no DC in the mains and none created by a faulty capacitor, then the DC has to be that “in phase”.

Looking forward to be quashed by the electricians.

Sven-Olof Jansson
London, UK; Boston, MA