hi every one
thats a popular question....in 3 phase machines when we use the nutral connection and earth connection??
i have compressor +fan(eveaporator)+heater
which one is needed for the last and which one is not??!!

 

You always need a ground (earth) connection to the chassis. If you do not have the chassis grounded, then it is possible for the chassis to be energized if there is a fault in the motor; ie: a winding becomes shorted to the chassis. If the chassis is grounded, then the winding's short will simply cause the circuit breaker to trip.

As far as your other questions; I am not an electrician. You should consult one.

 

Three and polyphase systems are dealt with here.

http://www.allaboutcircuits.com/vol_2/chpt_10/2.html

It is not labelled but the star point is connected to the neutral. The three phase connections go to the outer ends of the star windings.

The neutral is always there to carry the return current (if any) when the circuit is working normally.

The (local) Earth or ground should be connected to exposed metal parts and nearby exposed metal objects.
It is only there as a safety measure and should only carry current briefly in a fault condition. This fault current should operate the disconnection device, breaker or fuse.

 

hi every one
thats a popular question....in 3 phase machines when we use the nutral connection and earth connection??
i have compressor +fan(eveaporator)+heater
which one is needed for the last and which one is not??!!

if your machine works with 3 phase power then you dont need the neutral wire but you need the ground wire for safety. In your case, the compressor motor shall work on e phase power, i suspect the fan is single phase so you need one of the phases ans the neutral to make it work. Also, think the heater is single phase too. Thus, to make a 3 phase machine work you need only the 3 phase wires and to make a single phase machine to work you need one of the three phase wires and the neutral. In both cases you have to connect the ground wire to all metal parts of the machine for safety.

 

thank you sgwooki,studiot and mik3
for mike3
the fans and heaters are 3 phase

 

thank you sgwooki,studiot and mik3
for mike3
the fans and heaters are 3 phase

So you dont need the neutral wire here but only the ground wire. Connect it to all metal parts for safety.