Essential supply definition
Essential supply means that in case of a power interruption, standby power is either automatically or manually switched to these circuits from a standby power source. Special care shall be taken (a) to prevent any feedback from the "Essential" to the "Non-essential" supply or vice versa and (b) that fan motor starting current does not exceed the capability of the standby power source. If necessary, special precautions must be taken to limit the motor starting current.