PDA

View Full Version : Neutral carries current?







Drew
18-01-2013, 08:45 AM
I live in Australia where we have 3 phase 420volts and single phase 240volts.

On the Refrigeration systems I work on ( single phase 240v) if I take a reading with my ammeter on the live I get say 10 amps ,I will also get 10amps on the return neutral.

Electricians I speak to say that a neutral should not carry current unless the loads are unbalanced. This confuses me?

Are we referring to two different style neutrals , one being the single phase return to the main neutral, and the other is the main neutral. Does the main neutral not carry current if the 3 phases are balanced and then somehow cancel each other out.

Therefore if we have three resistive loads,all the same resistance ,each fed by a phase and say each draws 10amps. This 10 amps would be seen on each individual return neutral , but as soon as they join together on the common neutral bar the main neutral going on further would read 0volts as they have balanced out?

HVACRsaurus
18-01-2013, 10:42 AM
Hi. They are talking about neutral connected to star point of a balanced three phase load (motor or heater bank or such). With single phase, neutral should carry EXACTLY the same current as the line, else the current would be tracking to earth.

Drew
18-01-2013, 11:02 AM
Thank you, that makes it clearer.

BRETT
14-02-2013, 12:27 PM
hi drew yes single phase current taken on the active will be measured on the neutral also, if you measure eg 10amps on each phase of a balanced three phase load you will read zero on the neutral return but normally the system would not have a neutral in this case

NoNickName
14-02-2013, 12:39 PM
That of course doesn't mean you can touch the neutral, because its potential to earth may float.