I argued with him a little bit and told him if that breaker was being used on a AC 240 volt split phase circuit that each pole in it would be carrying 100 amps of the load. So why can't I do that on DC - run 100 amps thru each pole? He said you can, but it is not UL Listed for that and therefore he did not recommend it.
I could pull like 250 amps on it for a few seconds before it would trip but it would handle slightly over 200 without a problem and without tripping.
Seriously guys, part of the problem has been overlooked here.
If you'd said "isolators" I wouldn't butt in. But we're talking about BREAKERS.
Its easy to say "amps are amps", but DC is a very different animal to AC.
And "interrupting capacity" is hugely different to "carrying capacity".
Breaking a 240V AC circuit carrying 100A is a pretty decent job - but at least an AC arc is SELF QUENCHING. That is, at 50 or 60Hz, the arc actually extinguishes 100 or 120 times a second. As soon as the contacts get far enough apart, the arc goes out and stays out.
Breaking a 80-100V *DC* circuit carrying 100A is a very different animal. The arc doesn't extinguish. There is a HUGE amount of heat generated. It will quickly melt contacts, ruin spring material, burn breaker bodies, switchboards, cables and if you're not lucky - the whole installation.
DC rated breakers use various techniques to "pull" the arc into a quench chamber where it can be handled (and extinguished) quickly. Frequently this is assisted with magnets, and/or electromagnets (coils) within the breaker. Polarity becomes important as you will draw the arc into the quench chamber one way - or push it out into the breaker body the other.
Any decent, knowledgable engineer who knows his switchgear would be advising you to use the breakers within their design/test/certified range.