A wire pilot is generally economical for distances up to 5 or 10 miles, beyond which a carrier-current pilot usually becomes more economical.
P = 10 kW
VL = 400 V
IL = 20 A
3- phse power, P = √3*VL*IL*cosφ
cosφ = 10*1000/(√3*400*20)
In single phase energy meter,
Current coil is made up from thick wire having few no. of turns.
Pressure coil is made up from thin wire having more no. of turns.