Re: Explain 3 Phase

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:

> Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<deano-at-corridor-dot-net>
 
> Hi

> > So does that mean that between the hot holes in each set of two
> > outlets there is a 240v difference?or is that not the way it works?

	Not on most duplex outlets, as wired.  As noted below it CAN be
	done:

> each set of two outlets (known as a duplex receptacle) has a bus (shunt,
> some folks call it a shorting bar) connecting the hot side of the outlets
> together. Normally they are at the same potential. It is possible to remove
> the shunt and wire the two individual outlets on separate circuits as
> independent devices. This is very rarely done.

	Both can be wired to the same 110 leg, thru different breakers,
	allowing high current devices.  Or to independent 110v legs, leaving
	220.  There is a (little used) US Standard for 220 in a a 'duplex'
	sized shell.

> While deriving a source for 240V single phase from two 120V outlets is
> possible, it is not recommended practice for several reasons. The main
> reason is that if one of the circuit breakers trips, the other may not,
> still leaving the equipment energized.

	I believe 'code requires such arrangements to use a two pole,
	mechanically linked, breaker, so if one trips, the other does
	also.

	(on the 'phase' of the 110/240v:
		This seems to ALWAYS lead to confusion, usually
		due to semantics, rather than facts.

		FACT:
			The two legs are in phase.
			(think about it:  If they were not, there
			would be 0v, not 220v, across the outside...

		Commonly it is said they are 'out of phase', this results,
		usually, from hooking a scope up ab looking.  Scope doesn't
		lie, right?
		BUT:
		It IS connected to a center point.  This MAKES ends
		LOOK OUT OF PHASE.  It's an artifact of the hookup...
	
		If 4 probes, & four channels, are available, set up two
		differential channels, taking due care of which channels
		are inverting....

	best
	dwp