# Difference Between Single Phase and Three Phase

can any one tell me the difference between the 3 phase and Single Phase

three phase :

A:B
A:C
B:C

single phase

any two wire, without a third.

what's the voltage between two phases?
if i wanted to connect the relay between 2 phases should i use 230 volts or 440 volts?

3 phase can be in a star or delta (triangle).

Standard street 3 phase is in a star configuration. The centre of the star is the neutral.

Street wiring single phase is between neutral and one arm. This is 240v. Between the arms of the star it is 440 volts -- DEADLY VOLTAGE.

Weedpharma

if i wanted to replace the start and stop buttons with relays in DOL starter, which relay should i use 230 volts or 440 volts?

single phase

any two wire, without a third.

is it right or not?

Single phase is neutral plus a live phase.
Three phase is (optional) neutral plus three live phases at 120 degrees to each other.

You can split 3-phase into 3 separate single-phase circuits (that's how domestic
supply is provided in many countries).

You never put a single load between two live phases.

The neutral is optional to a 3-phase machine, but vital in single-phase.

Some countries use two-phase centred on neutral (USA for one) for domestic
supply, but all these derive from a 3-phase distribution network via transformers.

Looking at the circuit, the start button is switching a coil across two phases therefore when open there is 440volts across the contacts,

You MUST have relay contacts rated for 440v. Most standard relays are rated for contacts of 250v.

Weedpharma

anilkunchalaece, I can not read the words down below in your diagram. As far as I can see no one has answered your question. Lets start with Safety First. Please be careful with these voltages. Now, this starter will have a coil on it that you need to energize. Most of the time it says what voltage it requires on the coil. The starter may run a 480V 3ph motor, but will use 120V to turn it on. 120V is the standard now, but some of the older equipment uses 277V not 240. this is essentially 1 leg to neutral pending weather it is Delta or Wye. So the long and short of it you need to look at the coil to see what voltage it requires.

weldsmith:
anilkunchalaece, I can not read the words down below in your diagram. As far as I can see no one has answered your question. Lets start with Safety First. Please be careful with these voltages. Now, this starter will have a coil on it that you need to energize. Most of the time it says what voltage it requires on the coil. The starter may run a 480V 3ph motor, but will use 120V to turn it on. 120V is the standard now, but some of the older equipment uses 277V not 240. this is essentially 1 leg to neutral pending weather it is Delta or Wye. So the long and short of it you need to look at the coil to see what voltage it requires.

The OP has stated that he wishes to replace the "start" and "stop" switch. The coil of the relay that operates the contacts is unimportant. It is the voltage ratings on the contacts that is important.

In this case, the voltage of the supply has not been stated so I have assumed worse case of 240v per phase.
I believe (subject to correction) that America uses wiring with single phase 120v and two phase 240v.

With 240v per phase the voltage at the ends of the Wye configuration is 440v between the phases.

Make sure your relay contacts are rated at the voltage for your areas three phase wiring. The relay in the circuit is connected between two phases by the "start" switch so your contacts need to be appropriately rated.

Weedpharma

Hi, as Weedpharma has pointed out its the switches that are to be replaced.
If your normal single phase is 240Vac then your three phase will be 415Vac, so the relay will have to have 440Vdc rated contacts.
Can you please post a copy of your proposed circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?

Tom…
Merry Christmas

TomGeorge:
Hi, as Weedpharma has pointed out its the switches that are to be replaced.
If your normal single phase is 240Vac then your three phase will be 415Vac, so the relay will have to have 440Vdc rated contacts.
Can you please post a copy of your proposed circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?

Tom.......
Merry Christmas

I would probably go for 440Vac for an AC circuit.

Weedpharma

Hi. oooooooooooooooooooooooppppppsss
440Vac

Tom.....

"A" and "D" are just too close on the keyboards!

Weedpharma

All the keys are too close for my liking.

Gentleman, You have made this all to difficult what does the coil say! If it say 480, it needs 480, its labeled. I did not mean to confuse.

Hi, as Weedpharma has pointed out its the switches that are to be replaced.

If your normal single phase is 240Vac then your three phase will be 415Vac,
or check the coil rating of the contactor, it should be written on the coil terminals
or the coil body viewable through the side of the contactor
or printed on a sticker
or stamped or pressed into the contactor body.

The control relay you choose will have to have 440Vac rated contacts.
The coil voltage of the control relay you choose will be what ever voltage you are using to activate these relays.

Can you please post a copy of your proposed circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?

Tom…
Merry Christmas

I hope that is clearer