In article , Ted Edwards wrote:
jim rozen wrote:
But the compressor runs off of 240 volts. Don't you
need to put the scope across both hot leads?

You could use another transformer - any handy 240 to whatever and put a
light load on it. Ground one side of the secondary and hook the other
side to the probe.

If it really is split 240 and not two lines of a three phase service,
looking at only one hot from ground should have very little error in
phase. Ted

this is a small 1960 tract home, most likely _not_ a two phase power
feed, the voltages for the low side is normally about 123vac, it varies
but have never seen it as low as 115 but as hi as 127. i suppose that
is not very definitive, the date s/b, here in Dallas-Plano. i always
thought the low side of a 208 feed was 110v?

we have had to install autoxmfrs in the early days for some equip that
needed 120vac. teletypes were especially picky. i gather the modern
3-ph feeds supply a higher voltage (as i read this ng). i remember some
real confusion in the late 60s, discussing two phase motors, many (my
father included) had strong opinions as to what they were (or were not).
we were just a bunch of computer repairmen, not EEs, and we got roped
in over our heads on some installations. the custormer and the (remote)
boss expected that we know more than they did.

it is easy to isolate the house load for short periods, so i will try
the power meter thing before dragging out the scope, probably tommorrow.
that s/b interesting, regardless. --Loren