On Mon, 30 Apr 2018 17:01:59 -0400, Clare Snyder
wrote:

On Mon, 30 Apr 2018 16:15:16 -0400, Clare Snyder
wrote:

On Mon, 30 Apr 2018 15:25:57 -0400, wrote:

On Mon, 30 Apr 2018 12:35:03 -0600, rbowman
wrote:

On 04/30/2018 10:05 AM, Ralph Mowery wrote:
Most places that have equipment that uses lots of power in the US will
have 480 volt 3 phase equipment such as motors. The lights are most
often 277 volts single phase as that is the neutral to one hot leg of
the 480 volt 3 phase circuit.

We leased an old bakery where the freight elevator was 550. After 40
years of home repairs the 550 showed up in the damnedest places. I never
made any assumptions about what I'd find when I opened a panel.

The strangest panel for the uninitiated is 3 p corner grounded delta.
It will look exactly like single phase 120/240 (2 pole breakers, 2
hots and a white grounded conductor) except there will be 240 to
ground and you will have 240v 3 phase equipment hanging off of it.
The first time I saw it I took a minute to figure out what I was
looking at.
The only place you will see it is where there are pretty much all 3
phase loads and maybe some 240v L/L load.


600 volt 3 phase delta (no neutral) is also pretty common.

Also the old "wild leg delta" where one phase is center tapped to
give a standard single phase service for "office" use while providing
208 3 phase for "shop" loads.

AKA 3 phase 4 wire delta. Not common any more but was VERY common
years ago. Only 2 of the phase to neutral connections could be used
because the third "wild" or "high" leg was somewhere around 208.

Center tapped Delta is far from unusual here. It has the advantage of
supplying the full 240v on the line to line loads instead of 208. You
just look for 2 transformers on a pole and one usually larger than the
other.

http://gfretwell.com/electrical/red%...ansformers.jpg

The larger one supplies the 120/240 load.