Important differences between AC and DC Circuit Breakers

I read the article and watched the video.
They state that A.C. breakers cannot be used on D.C. circuits.
The explanation is interesting, and makes sense to me.
However, they do not state that a D.C. breaker cannot be used on an A.C. circuit, as might be the case when protecting the output of a Lionel transformer. The voltages we use may be a factor too,

This thread may get interesting as the folks more knowledgeable than I make comments.

One factor with the design of circuit breakers, (AC), is Amp Interrupting Capacity. (AIC)  Not so much related to how a circuit breaker works, a combination of electromagnetic and thermal,  but if the circuit breaker is capable of opening properly with a high surge applied.  Most standard home circuit breakers are rated at 10,000 AIC.  Commercial duty circuit breaker/and Main Circuit breakers,  can be 25,000 AIC and larger.   If a commercial power supply/transformer fails, creating a surge, hopefully household overcurrent protection can open properly.   The damage from these types of failure can be catastrophic.

I use automotive breakers on my system.  I've tested them and they react as I expect. If I want to protect a circuit for 10A, I use an 7.5A breaker.  A 7.5A circuit gets a 5A breaker.  Since these are automotive breakers, they are not rated for AC.  I use the lower rating to help compensate for the slow acting properties of the thermal breaker.

I researched this before I decided to go this route.  What I found is there are many AC/DC breakers out there.  But the specs are different.  As an example a breaker rated for 120VAC/10A may only be rated for 32VDC/10A.  The difference is explained in the OP's original article.  With that said, since the DC voltage rating is always lower than the AC rating, I felt safe testing automotive style breakers.  In my opinion, they do their job adequately when the voltage is kept at levels we use on our train layouts.

IMHO, the best protection is still the fast blow fuse.  I don't use them as much anymore thanks to my grandkids.  I would need a box laying around when they are over :-).  Magnetic or electronic breakers work well but get very expensive quick.

Also remember that a fuse or CB is designed to protect the power.  The arcing that occurs when a breaker is tripped causes the transient spikes that a TVS takes care of.  Breakers as close to the power source as possible and TVSs as close to our electronics as possible is the ticket IMHO.

Tony

The article illustrates breakers used in a mains panel as may be used in a large solar array installation (lots of amps at 48 vDC).  I doubt any of us would consider going into a hardware store and buying a mains breaker for a layout.

The panel mount breakers we typically use for layout power usually have both AC and DC ratings, and the AC voltage rating is generally higher than the DC - probably due to arc breaking considerations as described in the article.

ZW breakers are thermal .  They heat up and open - hopefully before the shorted load is damaged - but with power routed across traces on circuit boards within engines, the risk of damage is real and repairs expensive.  Use a fast acting or instant trip breaker.  There are many threads on this forum discussing suitable breakers.  I use Airpax instant trip.

"Also remember that a fuse or CB is designed to protect the power."

A thermal fuse will protect analog power in a ZW.  It will not protect overcurrent in engines.  When I ordered instant trip breakers, the distributor commented that the only use for those is to protect electronics downstream from the power source.  That precisely describes our operating environment.

I can attest that a thermal breaker in a transformer will not protect traces on circuit boards in an engine derailed and shorted on a switch.

If you read the article carefully you will see you can use a DC relay for AC but its not advised to use an AC relay in a DC circuit. For the current and voltage ratings used in 3 rail power it would not make that much of a difference anyway. 

AC current is self extinguishing which means when the voltage goes through zero, which is does 120 times a second, the arc created when the contacts open goes out. 

With DC the arc will remain until the distance between the contacts is greater than the voltage can bridge in the air dielectric. For 20 volts that distance is only around .001". 

Short answer, don't worry about it.

Pete