@SteveH posted:can you provide some examples of when using a 10A instant breaker might not be appropriate?
I realize some of this strays from your exact ask, context, and bounds, but spelling it out for the benefit of the forum at large:
- Any classic Lionel transformer (excepting a Z or ZW) or any transformer incapable of provisioning a minimum of 10A as this exceeds the transformer ratings
- When the downstream bus wire size is less than 14AWG
- Even the most power hungry postwar conventional trains, even illuminated, consume significantly less than 5 amps. Sure, you can exceed this with double powered AA units and whatnot, but I find that is the exception for most [conventional] setups and one could argue the typical setup for a ZW is to control two trains, one per outer throttle. Two 7.5A breakers, one per outer throttle would likely be perfectly adequate and prevent over-subscription and reliance on the 15A internal thermal breaker.
- Whenever the expected load is significantly less than 10A - say a village of LED lamp post.
- When a fault may incorporate more than one throttle/terminal/circuit, extra consideration may be warranted as multiple circuit paths and breakers are involved and need to all trip to stop all power.
- Its just a better practice to size for load. A blanket recommendation for 4x 10A breakers may incorrectly give the impression that there is a total of 40 A available and put a higher reliance on falling back on the internal thermal breaker. Encouraging the use of thought and understanding with respect to calculating/estimating loads and power distribution can only better serve the individual hobbyist and hobby at large.
@SteveH posted:I understand that with accessory loads the breaker should be sized for the intended load. I'm wanting to understand your statement about other inappropriate scenarios. Where it applies to protecting the train's electronics (with judicious use of TVS diodes)
That right there is the most common exception. Sensitive electronics don't live just in locomotives or track powered equipment. Accessory buses should be treated no differently, especially since it is much more common to have smaller sized wires (not in parallel feeders like track work) in the power distribution.
Now, with regards to a general dedicated 10A to the track for train recommendation, I can get behind that (given a sufficient power source) as you are right, it is a good universal threshold capable of running running up to even the MU trains in conventional or command environments off that throttle where it may be appropriate to limit this to one per ZW (not utilizing the other throttle outputs and thus not needing to actually put breakers on them).
I am also going to clearly state that I am not disagreeing with the idea that a low current train, even sub 1A, wouldn't trip a 10A breaker in the event of a direct short such as a derailment (provided the power source can deliver the necessary amperage).
Edit: One last comment - I'd rather see someone easily add 4x 10A AirPax Instant breakers to their ZW for each throttle rather than get paralyzed with electo-mumble-jumble.
