What do I mean when I say 120 or 240 volts?
120 volts can be in a range between 110 and 130 volts. In most
all cases power from a good power company will be around 120 volts,
give or take a few volts. The condition of the wires to your house,
the transformer, the connections in the main and at the receptacles
will all effect this voltage.
My GenSet, with very little load puts out a total of 131 volts.
According to Onan, this is "within limits".
So, when I talk about 240 volts, it can be in a range that is double
that of 120, or 220 to 260 volts. For the purpose of this entire
step by step procedure when I say 240 volts, read 220 to 250 volts
because I believe it's rather rare to see over 125 volts on a commercial
power line. Could be wrong, but that's been my experience.