phases

[wwhitney]

Corner grounded?

The algorithm I proposed doesn't depend on what conductor, if any is grounded. Any 3-wire delta would give you 3 equal voltage pairs, with different phase angles, so it would be called 3 phase.

Cheers, Wayne

 

[jim dungar]

Trust us to have three pages of arguments (so far) over what to call something that every one of us knows what is.

I would say the discussion is needed, based on the number of problems we have dealt with when people use local slang instead of industry standards.

 

[jaggedben]

Corner grounded?

Delta 3-wire. Grounding doesn't change anything.

 

[jaggedben]

OK, here's a counting method that works for all the standard systems below, although it calls 120/208V 3-wire 2 phase (which is plausible in my book, although it's a system only ever used for single phase loads).

Namely, write down all pairwise voltages between conductors. For the voltage with the highest count (up to small differences, and choosing the larger voltage in the case of ties, to be unambiguous), choose any pair to be phase angle zero, and plot the phase angles of all those pairs. The number of phases is the number of lines through the origin spanned by those vectors. I.e. the number of different phase angles up to sign.

2-wire: 1 phase
120/240V 3-wire: 1 phase
120/208V 3-wire: 2 phases
120/170V 3-wire: 2 phases
Delta 3-wire: 3 phases
Wye 4-wire: 3 phases
Hi Leg Delta 4-wire: 3 phases
2 phase 4-wire: 2 phases
2 phase 5-wire: 2 phases

Cheers, Wayne

Been thinking. Never a good thing.

Is there some reason that the following doesn't work for the same systems? I admit being uncertain about the last two.

- Write down all pairwise voltages between conductors.
- Find the highest voltage and count the pairs with that voltage (ignoring small differences). If there's more than one pair, that's how many phases are present.
- If there is only one pair of conductors with the highest voltage, and the other voltages add up to the higher voltage (or there are no other voltages, as in 2-wire), then you have one phase. If the other voltages do not add up to the higher voltage, you have more than one phase present. *

Seems a lot simpler if it works. Something the lay electrician can actually follow.

 

[wwhitney]

Seems a lot simpler if it works. Something the lay electrician can actually follow.

Nice, that works for all the cases enumerated in my previous post.

Doesn't work for 5-phase, etc., although none of the counting methods so far work for that. So perhaps worth noting that the second step is limited to "2 or 3 such pairs."

Cheers, Wayne

 

[Hv&Lv]

Delta 3-wire. Grounding doesn't change anything.

Yes, I know.
The comment was meant as a light stab at sarcastic humor.
Apparently it failed..

 

[kwired]

120/208 three wire been mentioned a few times as only single phase.

Yet it can be easily transformed to run a three phase load via open delta transformer.

I would also think is possible to build a "two phase motor" that operates at 120 volts each phase and run it from said supply.

 

[winnie]

120/208 is clearly by physics a polyphase system.

It is _used_ in the same fashion as a split single phase system, to serve residential loads.

It is _called_ 'single phase', IMHO because of the way it is used.

Don't try to find a consistent physical basis for this naming.

-Jon

 

[GoldDigger]

120/208 is clearly by physics a polyphase system.

It is _used_ in the same fashion as a split single phase system, to serve residential loads.

It is _called_ 'single phase', IMHO because of the way it is used.

Don't try to find a consistent physical basis for this naming.

-Jon

Same with the perfectly good physical definition of a neutral, butchered to also call the center tap of a high leg delta a neutral.

 

[Tulsa Electrician]

Let's not forget about 647.5.