How to calculate the rating of incomer for the multiple outgoings?

Question

e.g Outgoing loads 5HP S/D starter-7Nos; 10HP S/D satrter-5 Nos; 20HP S/D starter-8 Nos; 250A TP MCCB-2 Nos; 63A TP MCCB-8 Nos; 4HP DOL starter-12 Nos; 3HP DOL starter-3 Nos; 1000W heater-1No.

Answer 1

You did not state the voltage, so we cannot calculate the current for you.

You need to know how many of those loads can be on at one time, and calculate the total amperage for that case.  Once you determine that, then the incomer must be rated to handle them all, continuously.

Answer 2

(a) 7 nos of 5hp load = 7x(0.7457x5) = 26.0995 kw (as 1 hp = 0.7457 kw)

(b) 5 nos of 10hp load = 5x(0.7457x10) = 37.285 kw

(c) 8 nos of 20hp load = 8x(0.7457x20) = 119.312 kw

(d) 250 A TP MCCB can will be provided for load appx = 120 kw

(e) 63A TP MCCB can will be provided for load appx = 30 kw

(f) 12 nos of 4hp load = 12x(0.7457x4) = 35.7936 kw

(g) 3 nos of 3hp load = 3x(0.7457x3) = 6.7113 kw

(h) 1 no of 1000w water heater = 1kw

*now if you want to select the incomer for a,b,c....h seperately here is the example for selecting incomer for 'a' only:

total connected load = 26.0995 kw

as we know P(watts)=1.732xVxIxpowerfactor

Expected current flow = (26.0995x1000)/(1.732x415x0.8) = 45.3885 A

select the practical MCCB/ISOLATOR rating ,so your incommer is 50 A TP ISO/MCCB and the cable size shall be 4cx10 or 4cx16mm square.

*if u need an incomer for all the loads then TCL = 376.2014 kw(add a to h)

Expected current flow = 655 A

so the incomer shall be 800 A TP MCCB as its a next biggest MCCB after 630 A TP MCCB

the cable size shall be 2 runs of 4cx300mm square or 1 run of 1cx630mm square cable for each phase and neutral.

Please note that all the loads may not operate at the same time either in commercial/residential areas so u need to multiply maximum demand factor to the total KW and you may revise your incomer and cable ratings according to your actual requirement.