cctalk Digest, Vol 88, Issue 2

Scott Quinn compoobah at
Tue Jan 4 07:29:26 CST 2022

On Sun, 2022-01-02 at 12:00 -0600, Grant wrote:
> Where are you getting two /different/ phases?  --  Remember, the 
> different legs on residential 120/240 wiring are really the same
> single 
> phase.
> How do you get *two* /different/ phases without access to a *third* 
> phase?  There are only a few places in the U.S.A. (and I'm not aware
> of 
> anywhere else in the world) that actually have 2? power (where the ?
> are 
> 90? out of phase with each other).

I have seen some roads where the utility has 2 of the phases plus
neutral going down them, not true 2-phase power, but 2 phases 120/240
degrees apart with the third phase just not present. Every time I've
seen that it seems like fools economy, but I guess they figure twice
the loads for only one more wire.

Can't remember what it was called but I do remember seeing in some book
somewhere about a "phantom 3rd leg" or something where they used 2
wires with 120/240 degree phase separation into the transformer and
then the third phase "corner" was just floating and current would
"return" across the other two. As it was brought up in the context of
"make sure some yahoo didn't try this on your install and if they did
be very careful" and was delta-only I imagine it was not that common.

More information about the cctech mailing list