single-phase tri-phase

[carlossan]

Hi,

I recently change my job, and in my new position all the subjects are 120VAC, 208VAC, 220VAC, 230VAC, 240VAC, 480VAC, 600VAC, single-phase, bi-phase, tri-phase...

I'm studying topics in electricity right now, but I'm very confused with this:

Is there a way to know by looking at the voltage value, if the connection is single-phase, bi-phase, tri-phase? 2,3,4 wires?

Thanks,

David

 

[GMgerry]

If you have no clue at this point I would stay away from it and leave it to a pro,

 

[jml2665]

if you are in the USA, check with your local unions for some training programs in your area. As GMgerry stated, this is not a place to learn without some professional help

 

[IPTnewbie]

i didnt realize this was an electrical forum.

David you can get hurt or killed with this.

a short answer to your question is YES there is a way to know by looking. and you get it by being profesiionaly trained.

 

[CBasicAsslember]

In the US you will generally be dealing with single phase and 3 phase. As far as I know all residential power is single phase 220 to 240 with the center tap of the transformer as ground (3 wire). All the outlets in your home are wired from one of the 2 outside taps to the center tap to give you 110 to 120 volts. Special outlets can also be installed for dryers, stoves, and air conditionsers that require 220 to 240 volts.

Industrial power is often 3 phase and the voltage supplied by the power company can vary. In an industrial situation where no customer provided transformers are supplied the voltage of a single leg will be between 110 and 120 volts. The voltage value can in some cases tell you something about the how it is distributed. The 480 and 600 volt feeds will be 3 phase and will require a customer supplied step down transformer. By the same token 220 to 240 volts could be either single phase or 3 phase. To answer your question, sometimes you can tell by the voltage, sometimes you can't.

 

[mikeydidit]

Just doind a quick search on the web I found this site.

http://www.powertogo.ca/phases.htm

This has some good infomation in it. Like the others have stated, be very careful. I got into telecomm after working in our electric shop and got "LITE UP" with 277 a couple of times. I thought "their has to be a better way to make a living". Now it is just 68 DC volts for the most part. LOL.

"You don't stop playing because you get old. You get old because you stopped playing."

For the best response to a question, read FAQ222-2244.

 

[GMgerry]

Since we are on the subject I have a question to ponder for the day.

Why is it called single phase when there are actually two phases? Should it not be called two phase or dual phase?

 

[franklin97355]

The phase starts when the wave crosses the zero point going positive (usually) and ends when it does that again, hence single phase.

The answer is "42"

 

[CBasicAsslember]

Why is it called single phase when there are actually two phases?

We are talking power, there are not 2 phases. Residential power is supplied single phase 220 to 240 with a center tap transformer. The real power delivered is always positive. Put 2 equal value resistors from the outside taps to the center tap of the transformer. The power through either resistor will be in phase with the power in the other resistor.

 

[ISDNman]

But the same is true for 3-phase, natch.

The current and voltage on your example will be 180% out of phase.

I have always wondered the same question!

 

[CBasicAsslember]

But the same is true for 3-phase, natch.

Nope, 3 phase has 120 degrees between adjacent legs.

The current and voltage on your example will be 180% out of phase.

The current and voltage of a given leg will both have the same sign.

Power = voltage * current

Assume +/- 1 volt, 1 ohm

current = voltage/resistance

At 1 volt the current would be 1 amp.

Power = 1 * 1 = 1

At -1 volt the current would be -1 amp.

Power = -1 * -1 = 1

The power from both legs will be in phase.