Homework 3 phase to single phase

Baker1988 · Oct 12, 2012

Hi every one i was just looking for a bit of help i have been given some home work from college that i am not sure on, We have just started learning about 3 phase so not very good at it yet but i have been given home work i have to draw a circuit diagram and a wiring diagram for a balanced 3 phase motor going into a 3 phase isolator (i dont have to draw the motor i just have to start from the isolator) which then will go into a 3 phase board i understand that but the thing is i have to go from the 3 phase board to 2 seperate single phase consumer units (like a domestic consumer unit) the problem i have got is if it is a balanced 3 phase motor supply there will not be a neutral connector going into the 3 phase isolator or board so when i go to wiring the single phase consumer unit will i still have to put a neutral in as the neutral will just end up stopping in the single phase board and wont go anty where else as the 3 phase is balance i know that in a single phase circuit you need the neutral as the return path i just wasnt sure if it needed it when fed from a balanced 3 phase motor

any help to clarify this or even a link to a good web page would help thank you

Johnuk · Oct 12, 2012

mmmm college questions are annying glad ive done the college stuff years ago, ive had question where they have missed some of te question out lol

Knobhead · Oct 12, 2012

John, once you finish collage is when you start to learn to use the building blocks you are given.

Knobhead · Oct 12, 2012

deservices
1/ you answered your own question
2/ no it is not obvious! Have a look at Motors and you may learn something.

Baker1988 · Oct 12, 2012

Hi every one sorry for the late reply been at work, I am sorry for not making sence this is actually practical work in the work shop but i have to do the wiring/circuit diagram as home work.

this is what i am starting with it is already put up.

[ElectriciansForums.net] Homework 3 phase to single phase

and i have to make a materials list and circuit/wiring diagram for what i have to do
this is a rough drawing of what the finished product should be

i have to wire from the 100 amp isolator below the 3 phase board and my tutor said just assume the board is supplyed by a 3 phase balanced motor so i will not need a neutral from the isolator to the board.
i do not have to wire a motor or even draw a motor i just have to assume a 3 phase balanced motor is connectec into the main 100 amp isolator.
and as i said the only thing i am not sure about is when i wire from the 3 phase board to the single phase board will i have to put a neutral wire in as there is no neutral to the main 3 phase board

Silly Sausage · Oct 12, 2012

Ah... the mist clears!
I'm assuming your supply is on the left.
You need to run a 4 core cable from there (4th core being the Neutral!)

Baker1988 · Oct 12, 2012

no the supply is not on the left the supply is under the 3 phase board, the isolator on the left is just a swa cable from the 3 phase board to a isolator, i have been told by my tutor that i should not put in a neutral for the 3 phase supply as i should assume it is a 3 phase balanced motor so seen as i am not putting a neutral from the motor to the 3 phase board do i still put a neutral in the single phase board?

Silly Sausage · Oct 12, 2012

OK, wherever the supply is, you need to bring the N from there to the 3P board.
You're right, you don't need the N for the motor cct.

Bobster · Oct 12, 2012

You can't be supplying the 3ph DB from the motor.

Baker1988 · Oct 12, 2012

Archy Styrigg said:
OK, wherever the supply is, you need to bring the N from there to the 3P board.
You're right, you don't need the N for the motor cct.

ok thank you thats what i needed to know thank you

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