SteveH ... appreciate the research and insights of your series of posts.  I run Lionel Legacy Command locomotives.  I have been using ATO Smart Glow Blade Fuses for the past couple of years between my Z4000 transformer and Gargraves track ... https://www.mouser.com/datashe...datasheet-461533.pdf   My consists typically draw ~2 amps on the inner loop and ~2 amps on the outer loop.  Two years ago I opted to go with 5 amp ATO Smart Glow Blade Fuses.  The vendor rates them as "Medium/Normal Blow".  At the time I figured going with 5 amps would give me some margin for track short circuits.  I also have TVS's about every 7 feet around my two track ovals on a 15ft x 10ft track layout.  Have had probably 15-20  trips of my 5 amp ATO fuses in the past 2 years ... and ... so far, no known damage to loco electronics.

However, after reading through your post, I became a believer in the Airpax Snapac for a fairly reasonable cost.  I just went online to the site you identified and ordered the 5 amp Airpax Snapac circuit breakers     Having now compared the 5 amp ATO Smart Glow Blade Fuse datasheet time-current characteristics (in above pdf) to the very fast Airpax Snapacs, I expect the 5 amp Airpax Snapac will trip before the 5 amp ATOs for my normal track short circuit snafus.    I also bought a couple of 7.5 amp Airpax Snapac in case I start getting nuisance trips with the speedy-tripping 5 amp Airpax Snapacs. 

I will wire them up in series with my 5 amp ATO Smart Glow Blade Fuses.  I'll post my anecdotal experience with these Airpax Snapacs vs my ATOs upon receiving them and running my layout for a month or so.  We will see.

Thanks again for a well-done analysis.

Regards,

Tom

Tom,  I'm glad you found this topic to be informative and helpful.  Thank you for including your experiences with the ATO Smart Glow Blade Fuses and for your kind words.

I look forward to reading about your comparisons.

SteveH:

Thanks so much for all of this information. I am replacing my "fast blow fuses" with the Airpax Snapac instant trip units you identified.

So far I replaced 5 fuses and when testing found them to be very fast! My (brick) transformers are the Lionel 135 Watt units which is why I installed the quick blow fuses.

I considered replacing the 135 Watt bricks with 180 Watt bricks to have the faster breaker as many have attested to here on the Forum. Since I didn't need the extra power it made perfect sense to install the Airpax Snapac instant trip breakers for less hassle and cost.

To say the least, it has been quite annoying to replace a blown fuse after a derailment, particularly when guests were visiting. Now, re-setting a breaker is really a "snap"!

Best regards,

Stan

I just finished installing another 4 of these nice very fast breakers. Now all circuits are well protected together with a TVS on each:

Here is the power distribution center prior to the upgrade to the circuit breakers. It was a little tricky making the small panel for the breakers fit in the small space above where the fuses were, but wiring was pretty easy:

@stangtrain posted:

I just finished installing another 4 of these nice very fast breakers. Now all circuits are well protected together with a TVS on each:

Stan,  thank you for the update.  Your installation looks great!

Steve, I have a question.  I'm building a small portable conventional layout with one loop of track and one siding.  It is broken into 4 blocks so that you can switch from the running engine to one parked on the siding, so basically I'll only have one train running at a time.  Would one circuit breaker be enough protection for all of the track or should I put one on each block?  Oh, this is being built on a hollow core door, so it's a really small layout.

Thanks!

I think one breaker is sufficient for anything that fits on a door.

Thanks GRJ!  That's what I was thinking but it's good to hear it from the experts here on the forum.

I agree with John that one breaker for your layout should be sufficient, unless you're providing power with more than one source.  If you're using more than one transformer or multiple outputs (ie. one for trains and another for accessories), then I'd suggest one breaker per output, especially if you're using a post-war transformer.  What transformer(s) are you using?

The whole layout is designed to be powered by one transformer, either a PW KW, ZW, or an MRC Pure Power Dual.  The layout is designed so that they are all interchangeable.

Below are a couple of pictures so you can have a visual.  I hope I'm doing this right, it's my first time posting photos here.  The first one is an earlier picture and the second one is after I finished the frame and control panel.  The transformer just sits on the control panel when in use and is removed before the control panel gets folded up for transport.  I was just starting the wiring when I read about TVS diodes and circuit breaker protection here on the forum.  My last layout was about 25 years ago and all I used then was what ever my transformer came with.  And yes, I do think I have a thing about toggle switches.

@31charlie posted:

The whole layout is designed to be powered by one transformer, either a PW KW, ZW, or an MRC Pure Power Dual.  The layout is designed so that they are all interchangeable.

Below are a couple of pictures so you can have a visual.  I hope I'm doing this right, it's my first time posting photos here.  The first one is an earlier picture and the second one is after I finished the frame and control panel.  The transformer just sits on the control panel when in use and is removed before the control panel gets folded up for transport.  I was just starting the wiring when I read about TVS diodes and circuit breaker protection here on the forum.  My last layout was about 25 years ago and all I used then was what ever my transformer came with.  And yes, I do think I have a thing about toggle switches.

Charlie,  while not necessary, you could power the uncouplers from another (Aux) source than the one controlling the trains.  That would allow you to supply the optimal 10-12 volts to the uncouplers while providing independent speed control the the train either conventionally or 18v for TMCC/DCS/LionChief.  In any case, a second breaker could optionally be used for the Aux power.

Hi SteveH,  Thanks for the idea.  I've thought about powering some things on the layout from another source but since I want this to be portable I think I'll just use one transformer to power it all.  With my KW I'll have 190watts available, and more with the others if I use one of those, I don't think I'll over tax any of them with what I have.  Everything I'll be running will be in conventional transformer control except for when I use a LionChief engine which I can still power with any of the transformers I'll be using.

Please let me know if you have any more thoughts or ideas for me.  I'm at the point where I'm ready to start wiring things up.

@31charlie, I don't want to belabor the point, just trying to ensure sure you understand your options.  You could use any single one of the 3 transformers you mentioned to provide power separately for the trains and for auxiliary devices.  Each one of those (ZW, KW, and MRC-Dual) transformers has multiple outputs.  Each output could use its own external breaker if you don't want to rely on the breaker built into the transformer.  My thinking was that I'd pay about as much for shipping as one breaker costs, so I bought a few more than I thought I'd need.

But, again the choice is entirely up to your personal preference.

Hi SteveH, So your saying to put a breaker on every feed from source to the load?  Even for accessories?  I must admit that I didn't really think of this before, I was only thing about a train derailing or some thing like that.

@31charlie posted:

Hi SteveH, So your saying to put a breaker on every feed from source to the load?  Even for accessories?  I must admit that I didn't really think of this before, I was only thing about a train derailing or some thing like that.

I'm not saying you should.  Rather, that I would since there is a chance that a misaligned pick-up shoe or roller could catch the accessory power from one of the auxiliary rails on an operating track.  If that happened, the only thing to cut the power would be the transformer's internal breaker. The PW ZW and KW are slow to trip, and take long enough to melt the insulation on small wires in modern locos and accessories.  I'm not sure about the speed of the MRC's breaker.

In other words, adding additional breakers (one per connected output) is cheap insurance if you're already planning to buy/install one breaker anyway.

I agree with Steve here, if you have separate accessory power being used, it is a good idea to have better circuit protection than a postwar transformer offers.

Thanks SteveH and GRJ!  I never thought of about the accessories causing a problem.  I'll be adding breakers to all the circuits on the layout.  It looks like the Airpax breakers will perfect for my needs.

I'm really glad I ask about this before I started the wiring, this has the potential to save me a lot of problems in the future.  Thanks again to the OGF, this really is the best resource for information on O gauge trains!

Since the subjects of PSX-AC circuit protectors and TVS (Transient Voltage Suppression) Diodes seem to come up frequently around this topic, I'm including a link here to another helpful discussion on those topics:

TVS and Fast Acting Circuit Breaker help

I would just like to add that I use two PC power supplies to power almost all my accessories. I can't attest to the exact type, but they have electronic circuit protection. I can short a 30 awg wire and it trips instantly. I use a 3 amp thermal breaker to protect small wiring, but it has never tripped. I use the 12v and 5v taps for all relays, signals, and lighting (90% led).

For anyone looking for fast circuit protection this time of year, I've added a few updates to the original Topic including the diagram below showing a simple example for how to connect a circuit breaker and TVS diodes.

For convenience, here is a link back to the beginning of this thread.  Airpax Snapac "Instant" Hydraulic-Magnetic Circuit Breaker Internal Mechanisms

@SteveH posted:

The P&B is also heat dependent, where the Airpax isn't.

Hum!  A tangential question:  Are automotive self-resetting breakers, such as used to upgrade the internal breakers in ZW transformers, heat dependent as well?  If so, that may explain a problem I've had in the past where a ZW has been running for a few hours and then the upgraded breaker pops with no provocation... 

Mitch

@M. Mitchell Marmel posted:

Hum!  A tangential question:  Are automotive self-resetting breakers, such as used to upgrade the internal breakers in ZW transformers, heat dependent as well?  If so, that may explain a problem I've had in the past where a ZW has been running for a few hours and then the upgraded breaker pops with no provocation... 

Mitch

Most of those style breakers are thermal breakers and are just fine for protecting the transformer as originally engineered and intended.

These AirPax breakers are external breakers and strategically sized and placed for sub circuit protection and of course, are very very fast in tripping and can be considered as adding some additional downstream protections.

Any thermal breaker is "heat" dependent.  OTOH, they have a fairly wide operating range, normal temperature ranges shouldn't affect their characteristics enough to make a difference.

Here's the temperature de-rating chart.

Steve-

i am going to order 4 of the Airpax “ instant” breakers as per your great research and postings. Question: I have a 275 watt ZW that I was going to put the Airpax breakers in each of the A, B, C, D outputs— I cannot decide on either the 7.5 or 10 amp versions. Any recommendations?

Carl J

One sizes these external breakers for the expected load, not to the transformer (although the total load must not exceed the transformers capabilities - in this case 12 Amps continuous, 15A max for a ZW).

Well, what are you going to run?  Typically, you'd have no more than a maximum of 10 amps on a single output.  If you run conventional, I'd go with a smaller rating, it's unlikely one train would get anywhere close to 10 amps if it's running normally.

@Carl J I'm using the 10A with my PW ZWs for track power.  Presently Online Components is out of stock on the Airpax Instant 7.5 Amp breakers.  There are other distributors for Sensata/Airpax, but beware similar part numbers that are not of the Instant variety (see earlier replies).  Maybe someone can find the 7.5Amp Instant elsewhere.

For accessories a lower current rating may be better depending on which and how many.  The 5A may work for those, depending on the required power.

I prefer the 10Amp breakers on the postwar ZW for track power because they allow more operational flexibility, ie. more than one locomotive (conventional, LC, and/or Legacy) on a power district track a time with smoke and incandescent lit passenger cars.

In a more general sense of choosing a breaker's current rating, as long as the transformer's output current rating is not exceeded, any of the Instant breakers will trip immediately in the event of a derailment.

When TVS diodes are installed appropriately, I'm inclined to believe there's little benefit to choosing a smaller breaker for added train protection, if the selected instant breaker is rated approximately 20% less than the Postwar transformer's maximum output current.  Thoughts?

@SteveH posted:

I'm inclined to believe there's little benefit to choosing a smaller breaker for added train protection, if the selected instant breaker is rated approximately 20% less than the Postwar transformer's maximum output current.  Thoughts?

There can be perfectly acceptable scenarios that lend themself to having a ZW with four 10A breakers hanging off of it and there are others where that would be inappropriate. That is why I always recommend, with the goal of protecting the downstream equipment, one sizes the instant breakers to the downstream load and never let the total load exceed the transformers capabilities (sure a 20% de-rating parameter can be utilized in determining the capabilities).

Is the Airpax Snapac Instant circuit breaker 10A the only one will work with ZW?  Or is it the best.   I have TE connectivity P&B 8A push to reset/ circuit breaker will they work?  I’m still new with stuff.

@Stephen G, you don't provide an exact model number or series of the breaker. The common ones seem to be W28 and W58 (and there are others I am sure) and those are thermal breakers and do not even compare to the instant breakers discussed here. If your goal is protecting downstream equipment with some of the fastest trip times reasonably obtainable, these AirPax are the bees knees and are what I have been using personally for 7 years or so now.

They were  W28’s.  Airpax Snapac Instant 10A it will be then. Thanks you guys for the information.

@bmoran4 posted:

There can be perfectly acceptable scenarios that lend themself to having a ZW with four 10A breakers hanging off of it and there are others where that would be inappropriate. That is why I always recommend, with the goal of protecting the downstream equipment, one sizes the instant breakers to the downstream load and never let the total load exceed the transformers capabilities (sure a 20% de-rating parameter can be utilized in determining the capabilities).

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), can you provide some examples of when using a 10A instant breaker might not be appropriate?

@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.

@bmoran4 Thank you for your excellent and detailed reply.  I agree with all of these assertions.

First off, I personally wouldn't be configuring my power so that I had one transformer that maybe delivers 12-13 amps powering four power districts that had 10 amp breakers.  That's the very reason I power each power district with a transformer that has the full capacity of the circuit breaker for the power district.

In the scenario of the ZW, I'd probably consider a common breaker of maybe 15 amps for all the circuits replacing the lousy ZW circuit breaker.

Four 180 watt transformers, and four 10 amp breakers, the way God and nature intended it to be.

@gunrunnerjohn posted:

Four 180 watt transformers, and four 10 amp breakers, the way God and nature intended it to be.

That is all and well great, but not everyone is in strictly command la-la land with empires needing 40A of track power. This thread documents a different solution for different needs.

@gunrunnerjohn posted:

First off, I personally wouldn't be configuring my power so that I had one transformer that maybe delivers 12-13 amps powering four power districts that had 10 amp breakers.

Absolutely no general argument from me on that!

@gunrunnerjohn posted:

In the scenario of the ZW, I'd probably consider a common breaker of maybe 15 amps for all the circuits replacing the lousy ZW circuit breaker.

I have rarely found a internal breaker that is outside of Lionel's spec - I find more often people are surprised at Lionel's spec. However, it serves it purpose as intended - to protect the upstream transformer. So instead of modifying a perfectly serviced and usable ZW, just supplement it externally with the Instant AirPax units as discussed in this thread with sub circuits strategically sized for the expected load and keep the total load below a constant 12A and under extended 15A peaks. This can also add cross throttle/circuit/terminal fault protections, something lacking in many classic transformers.

"Four 180 watt transformers, and four 10 amp breakers, the way God and nature intended it to be. "

Will golly, I was debating getting a fourth brick, I'll take that as a sign.

@illinoiscentral posted:

"Four 180 watt transformers, and four 10 amp breakers, the way God and nature intended it to be. "

Will golly, I was debating getting a fourth brick, I'll take that as a sign.

I'm glad I inspired you.

Micro-Semiconductor (shipping from Hong Kong) appears to have the 7.5Amp Airpax Instant breakers in stock.  I have no history ordering from them.

Micro-Semiconductor link:  Airpax 7.5 Amp   PP11-0-7.50A-OC-V

Online Components, Digi-Key, Mouser and all other distributors listed on Octopart.com are presently out of stock of the Airpax 7.5Amp  Instant breakers.