Triping time of MCB used in a single phase circuit

[400245sai]

I am working for a lighting design in a petrochemical industry. The Lighting circuit is a three phase in main lighting board and each theree pahse circuit is further taken to a junction box in the field and from this junction box single pahse circuit goes to each light fitting.These light fittings are connected between pahse and neutral.
The cross section of cable from main LDB to Junction box is 4c16sq.mm copper and from and from junction box to fitting it is 3c 4sq.mm .one core for the phase and the other for neutral and third for earth core.
The supply volatge in three phase is 415V and in single pahse is 220volts.
I have calculated the fualt current at the fitting considering the cable resistance from Main LDB to the fitting and this is divided on 220Volts to calculate the fault current. It comes to 194amps.
I have selected a Merlin Gerin MCB C60N with type C curve.
The curve is enclosed.
My qustion is at what time this MCB would trip in the system for the above fault.?
Whether any where in the band width indicated for MCB curve for tripping can be taken as tripping time?
For a pahse to neutral fault whether my working of dividing on 220V the cable resistance both ways is correct?

 

[jbartos]

Suggestions marked ///\\400245sai (Electrical) Feb 21, 2003
The cross section of cable from main LDB to Junction box is 4c16sq.mm copper and from and from junction box to fitting it is 3c 4sq.mm .one core for the phase and the other for neutral and third for earth core.
The supply volatge in three phase is 415V and in single pahse is 220volts.
I have calculated the fualt current at the fitting considering the cable resistance from Main LDB to the fitting and this is divided on 220Volts to calculate the fault current. It comes to 194amps.
I have selected a Merlin Gerin MCB C60N with type C curve.
The curve is enclosed.
My qustion is at what time this MCB would trip in the system for the above fault.?
///The circuit breaker may trip anywhere along the vertical line drawn from 194 amps crossing the bottom circuit breaker time-current curve, t=Tlow to the top circuit breaker time current curve, t=Thigh.
The region inside the curve represent the circuit breaker time margin, in vertical direction (time axis), in which the circuit breaker would trip.\\Whether any where in the band width indicated for MCB curve for tripping can be taken as tripping time?
///Time may be anywhere from the bottom circuit breaker time-current curve to the top circuit breaker time current curve.\\For a pahse to neutral fault whether my working of dividing on 220V the cable resistance both ways is correct?
///It is correct for the two-conductor circuit, 220V phase to neutral, single phase. Three-phase circuit having the three phase balanced fault, the circuit comprises of only one forward conductor length. The return length consists of balanced three-phase fault currents that amount to zero. Therefore, the return current path is not in existence.\\