"Harry Bloomfield"; "Esq." wrote in message
...
NY presented the following explanation :
so the power lines are at + and - 55 V wrt earth (*).

Not +ve and -ve, it is ac.

Sorry, I thought I'd covered that in my asterisked footnote. I know it's AC.
What I meant was that the two wires to the appliance are not at 0 and 110 V
(RMS) wrt to earth, but instead are each at 55 V RMS with opposite polarity
wrt earth. I was using "+" and "-" as shortcut for that.

So for example there will be an instant when one wire is at + 77 V (55
sqrt(2)) and the other is at - 77 V wrt earth. Half a cycle later, the first
will be -77 and the second will be +77. There will still be 144 V peak or
110 V RMS between the two wires, but only 55/77 wrt earth.