two phase or single phase

When you lose a phase on a three phase system it is referred to as single phasing.

Each hot leg is not a "phase". The potential difference between any two hot legs on a three phase system is a "phase". A to B is one phase, B to C is one phase, and C to A is another phase. In total, they comprise three phase.

If you lose one leg, for instance the C leg, you'll only have single phase from A to B.

I think the last North American two phase generation went offline about 1981, so it's hardly worth discussion. It's a horse of another color.

2 phase or single phase

thanks guys your answers will be apreciated:thumbup:

MDShunk said:

I think the last North American two phase generation went offline about 1981, so it's hardly worth discussion. It's a horse of another color.

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I have never seen 2 phase myself but I was wondering since you mentioned it went off line in 1981 why the nec still lists it for motor loads. If it's no longer used it would be nice if they removed all reference in the code to two phase.

But then re-thinking this maybe some equipment still in use converts to two phase for there equipment by using some kind of converter.

Some Welding equipment is 2 phase.

Frank

This is 2 phase which is called a "scott-tee" transformer connection.
You have 3 phase on the primary side and two phase on the secondary side. 1-2 is one phase and 3-4 is the second phase. You have to be carefull and follow phasing on the secondary side or you will get some weird voltages. There is also the problem of getting some very high fault current on the secondaries.

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we still have five-wire two phase in Philadelphia
I love the followup calls after somebody sticks a three phase motor on a two phase service without a changer...
Once had somebody burn up an elevator motor by paralleling a 3-phase compactor with it... sort of worked like a scott winding for a while..
http://www.3phasepower.org/2phasesystems.htm

apparently, the delta concept is going to go the way of the world as well ...

jorge said:

is two hot lines out of a three phase system called 2 phase?

any info will be apreciated:laughing:

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two Legs is called single Phase, Three is called Polly Phase (three) phase