110V DC cable and MCB sizing calculation

[byju1982]

Hi,

We are sizing the DC cables from DC Distribution board to the switch-gear and also the interrupting device (MCBs) at distribution board and load terminal. I understand we should use only the continuous loads for this purpose. Is the momentary load like CB closing coil , trip coil currents etc that last for only 80 ms approx required to be taken into consideration for sizing the cables and MCBs ?

Thanks in advance,

Bvc

 

[ScottyUK]

You certainly need to consider cable volt-drop, especially for any large transient loads like tripping coils or, in the case of old gear, closing solenoids.

If you have a large standing load you may be able to disregard your transient loads when sizing the battery itself, although you still need to make sure that the chosen cells can deliver the peak current without damage. Peak tripping load can add up to a fair bit of current in a large substation with bus zone protection or a breaker fail scheme which could both command simultaneous operation of many breakers, for example.

 

[byju1982]

Thanks Scotty !
What is the authoritative standard on this subject ? That is for sizing of DC MCB, DC feeder to trip, alarm-indication and Control circuits.