On Mon, 19 Aug 2013 17:31:29 -0700, Dan Coby
wrote:

On 8/19/2013 11:08 AM, Markem wrote:
On Mon, 19 Aug 2013 13:43:36 -0400, "Mike Marlow"
wrote:

Correct me if I am wrong, but you seem to be focused on a phase shift in
your use of the term "phase", which is not the only proper use of the term.

Both legs of a 240V are 120V each, if you look at them on an
oscilloscope the peaks and valleys match each other, they are in phase
with each other, ...

When you use an oscilloscope to look at the two hot wires of a 240 volt circuit
(in the US) you will see that the positive peak of one wire corresponds to the
negative peak of the other wire and vice versa. (This assumes that both signals
are measured relative to the neutral.) I.e. one signal looks like the other
signal plus a 180 degree phase shift. The two signals are commonly referred to
as being 180 degrees out of phase.


Dan

PS: If you actually try this experiment, please use some caution. Most
oscilloscopes are not designed to handle this high of a voltage on their
inputs. Also incorrectly connecting the signals can result in dangerous
high voltages in unexpected places. I.e "Please read and understand all
of the safety information related to the use of your equipment."
Simple, safe way to "play in the sandbox". Get yourself a simple
center tapped fillament transformer out of your "way back box" - or a
transformer from a full wave rectified (non bridge) power supply.

Then plug the primary into the 110 volt SINGLE PHASE power supply.
You now have a low voltage version of the north american 3 wire power
distribution system with a safe approxemately 12 volt (depending on
the transformer) output that you can play with on the scope. If you
want to go a bit farther in your "playing" get 2 bell transformers, or
other low voltage single secondary transformers and connect the
primaries in series, then check the "separate" secondaries - which are
in effect a split center tapped winding that you can connect in phase
and 180 degrees out of phase by simply changing the connection. Each
secondary will give you, say, 10 volts when separated, and either 0 or
20 when connected, either in or out of phase - however you want to
define that.