On Wednesday, August 8, 2018 at 12:17:52 PM UTC-4, Mark Lloyd wrote:
On 08/07/2018 07:47 PM, wrote:

[snip]

If you have 3 conductors (one of which is neutral), how would you
determine if the others had the same phase or different phases? No
cheating please.

There are 2 possibilities right away.
That is where you actually need to understand the distribution systems
used in the US.
I would need to determine what kind of system I was looking at. Simply
poking around with a meter or even a scope, is not going to give you
that answer unless you understand that.

I did actually leave out something, that the 2 non-grounded conductors
carry the same voltage at the same frequency.

That and a voltmeter is all you need. There's no need to bring in
extraneous information, like power distribution systems.

Thank you!




If the 2 conductors carry the same phase, the voltage changes (AC) are
in step, so at any time they have the same voltage on them. The
difference is 0V and that is what you measure. No need for any of that
complex stuff, like where those conductors came from. It works the same
if you have 2 synchronized electronic inverters with a DC supply.

BTW, 240V is NOT the same as 0V.

Also, I remember someone talking about synchronizing generators by
putting a light bulb between the outputs. Same phase: no light.

[snip]

--
Mark Lloyd
http://notstupid.us/

Thank you again. That's exactly what I said, if you have two AC conductors
that are delivering power and they are the same phase, voltage and
frequency, you can parallel them, because there is no potential difference
between them. And what you have coming into a house with 240/120
service looks like two 120V voltage sources that are out of phase
with each other by 180 deg, or of opposite polarity, same thing.
It actually is that. By viewing it as that, all is explained:

A - With respect to the neutral, you see two 120V voltage waveforms with
respect to the neutral, differing in phase by 180. And that's exactly
what is there, each half of the secondary winding is a voltage source
and they are connected with opposite polarities with respect to the
neutral.

B - You can't randomly parallel any two 120V receptacles in the house
because some are on opposite phases.

If you measure between the two phases, you get 240V.

All that flows directly. There is no need to talk about transformers,
generators, or a synthesizer, if it happens to be created by an
electronic UPS type device, etc. If you add in ampacity, that voltage,
phase, freq info is all you need to design with it and use it.