single phase 208v neutral

[Matt B]

IN a single phase 208v application in most cases no neutral is needed, is there no return path. No one has explained this to me properly. Also is what is refered to as a "common" wire another term for neutral.

 

[charlie b]

If you start with a three phase, 120/208 volt system, and if you connect a load between two phases, you will get 208 volts to the load, and the neutral wire will not be part of the circuit. Any current that flows from the source via one ungrounded conductor, and passes through the load, will return to the source via the other ungrounded conductor.

So there is a ?return path,? and you don?t need a neutral to have a ?return path.?

I have heard the word ?common? used in connection with DC systems, but not in connection with AC systems. I have also heard (long ago) the phrases ?hot leg? and ?cold leg,? referring to the phase conductor and the neutral. The correct terms are ?ungrounded conductor? and ?grounded conductor.?

Does that answer your question?

 

[Dennis Alwon]

IN a single phase 208v application in most cases no neutral is needed, is there no return path. No one has explained this to me properly. Also is what is refered to as a "common" wire another term for neutral.

Charlie is absolutely correct. I have heard of "common" being referred to as the neutral or grounded conductor. It is not good terminology because it can mean many things.

 

[jtester]

IN a single phase 208v application in most cases no neutral is needed, is there no return path. No one has explained this to me properly. Also is what is refered to as a "common" wire another term for neutral.

I wouldn't make that statement relating to 208 volts. I often do an apartment complex with a 120/208 volt 3 phase service and 120/208 volts single phase to each apartment. These have a neutral and provide 120 volts for lights, receptacles, etc. I can use 208 volts without a neutral, but I regularly have a 120/208 volt single phase system with 2 hot wires and a netural.
I have heard the neutral referred to as a common, but agree with Charlie and Dennis that it is more often used for a dc system.

Jim T

 

[brian john]

jtester:

The term single phase with 208 is common terminology and I believe by definition meets the criteria.

Three phase - 120/208 3-phase 4 wire wye
Which allows:

3-phase 3-wire 208 VAC
Single phase 2-wire 208 VAC
Single phase 2-wire 120 VAC


In addition what you describe, 120/208 2 p hases/ 2 ungrounded conductors and a grounded conductor (3-phase 3 wire) is commonly referred to as single phase.

Not positive if all these meet the definition of single phase, but the terminology is utilized, of course as noted in another post some lay people call the neutral/grounded conductor a common.

Will research this when I get to my office.



http://www.windstuffnow.com/main/3_phase_basics.htm

 

[jtester]

Brian

In my post I was cautioning against thinking that 208 usually didn't need a neutral. I didn't mean that it couldn't be single phase. I'm sorry for the confusion.

In this area, if someone tells me it is a 208 single phase system, I can't assume it doesn't have a neutral.

Jim T

 

[brian john]

Single phase 2-wire 208 VAC SINGLE PHASE TWO WIRE CIRCUIT
Single phase 2-wire 120 VAC SINGLE PHASE TWO WIRE CIRCUIT
120/208 2 phases/ 2 ungrounded conductors and a grounded conductor (3-phase 3 wire) . SINGLE PHASE THREE-WIRE CIRCUIT


All of these terms have a definition in the IEEE dictionary and a somewhat similar definition in the "dictionary For The electrician With formulas" by Tom Henry

 

[jtester]

.....120/208 2 phases/ 2 ungrounded conductors and a grounded conductor (3-phase 3 wire) . SINGLE PHASE THREE-WIRE CIRCUIT


All of these terms have a definition in the IEEE dictionary and a somewhat similar definition in the "dictionary For The electrician With formulas" by Tom Henry

Why do you call that (3 phae 3 wire)?

Jim T

 

[barbeer]

Brian

In my post I was cautioning against thinking that 208 usually didn't need a neutral.

Jim T

I believe Charlie B was referring to Utilization equip. (i.e. motors, heaters....) not necessarily a feed to a sub panel. I believe it was well explained by him.

 

[jtester]

I believe Charlie B was referring to Utilization equip. (i.e. motors, heaters....) not necessarily a feed to a sub panel. I believe it was well explained by him.

I agree.

Jim T

 

[brian john]

JimT typo....My Mother always told me to take typing. In the 60"s I never saw a need for it.

 

[johnny watt]

I think it?s important to remember that current will flow between two points of different potential if given a path to do so. One of those points can have a potential of zero volts with respect to ground but of course it is not necessary. In a single phase 208V circuit with no neutral, the two voltage lines are alternating from negative to positive in voltage and they are doing so at opposite times with respect to each other. That is why current flows without a neutral.

I have heard the term common used mostly for DC but occasionally I see it used with AC such as the low voltage transformer of a doorbell, furnace or thermostat. Perhaps every neutral is a common but every common is not a neutral. In my mind, common implies that half the circuit shares the conductor and the other half does not. So I do not see a neutral as a common unless it is a split phase or poly phase system or there is a bus or chassis as the conductor. Simply being at neutral potential is not enough. Just my opinion...