Answer / rahul

3 Phase 4 wire means 3 phases R,Y,B and a neutral, so it is usually used if you need a single phase voltage. For a 3 phase load need just 3 phase 3 wire system.

Answer / sharaf

yes...an extra earth wire in 3 phse 4 wire systm protects
equipments frm earthing

Answer / suraj chawardol

We should have clear concept regarding where 3 phase 3 wire system used and where 3 phase 4
Wire system used
1.3 phase 3 wire system= In India electrisity is generat at 11 or 33 kv.then it is step up with the help of tranformer. To transfer it from generation station to substation 3 phase 3 wire system is used. Then it is step down at substation or directly feed to application having such rating. Genarally 11 kv feeder are brought near to distrubution transformer near to load ( near to home genarally called DP). The input to distribition transformer is 11 kv feeder and output of transformer is 440 v , 3 ,phase 4 wire system. ie 3 phase R,Y,B and one neutral.
2. 3phase 4 wire system = the secondary side of transformer is star connected so line voltage become 1/sq root 3, ie near 240 v . Our home appliances are design to work at Approximataly 230 v ,50 hz so we need any one phase and neutal for single phase load .
3. Also for high power application we need 3 phase 3 wire system such as Induction motor.
4. Both the system have its own importance depending on applications.

Answer / ashok mishra

question is which one is more reliable??

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