NEC 250.169 Ungrounded Direct-Current Separately Derived Systems..., related for fire alarm systems

[DM2-Inc]

I'm trying to understand if the DC circuits of a fire alarm system fall under section 250.169.

As I understand this section, it's requiring bonding jumpers on "non-current-carrying metal parts" for "...Separately Derived Systems" (SDS). I don't think I have a good understanding of what a "Separately Derived Systems" is. The section references "...stand-along power sources..." and "..engine-generator set...".

It would seem to me that when the panel is operating off of the 120 VAC dedicated breaker, it's not a SDS, but it becomes an SDS when the AC power is lost and the system is running on batteries.

Have I got this right?
...because of the batteries, all of the "non-current-carrying metal parts" have to have a bonding jumper?

 

[don_resqcapt19]

Unless there is a common circuit conductor between the AC supply and the DC system, it would always be a SDS. Not sure there is any need for the boding shown in 250.169, but I don't see anything in 760 that modifies that.