Legacy protection using Postwar ZW

Because the Legacy base is connected passively to the layout, there is no further protection needed. There is no operational current drawn through it, and it connects with just one wire for communication.

The ZW has its own breaker protection as you have described, on the "U" side(all 4 are the same) and will protect the ZW and the appropriately sized layout wiring.  If you want breakers in-line with the A-B-C-D outputs, this can be handy so if one line/district trips, it doesn't shut down the whole layout.

The Legacy base will be fine.  The Legacy engines or other modern engines for that matter probably will not be.  Fast acting fuses could help prevent the modern electronics from getting fried if a derailment happens.  The PW breaker will trip...eventually  but probably not in time to protect the engines wiring or circuitry.  

I would definitely add the inline fuses at minimal or get a modern transformer that has quick protection built in.

I also suspect that the drops may not help much. Depending on what you are running, with smoke units and lights you may be reaching the limit of the older transformer or maybe run the switches from another transformer.

BruceG the gentleman you need to consult with would be GunnrunnerJohn. He has given me great advice and assistance with my layout where I am using two PW ZW one a 275 W and one a 250W. But I am running MTH DCS system so I would not want to advise you to do what I am doing as the protection required for the two systems is a little different. Part of what you want to be concerned about is not just the Base Unit and your ZW but the electronics in the locomotives which the CB in the ZW may not be fast enough to protect the locomotives. It is there to protect the ZW.

I am using American hobby distributors PX-1AC   I have two of them  very fast and have auto reset or manual. AMhobby.com  got mine thru Tonys Train Exchange , they are big into command control for most scales.

@MartyE posted:

 I would definitely add the inline fuses at minimal or get a modern transformer that has quick protection built in.

@RJT posted:

not just the Base Unit and your ZW but the electronics in the locomotives which the CB in the ZW may not be fast enough to protect the locomotives.

@Rick Rubino posted:

...PX-1AC   I have two of them  very fast and have auto reset or manual...

There is no circuit breaker or fuse fast enough to protect the on-board train electronics form high voltage spikes. Breakers are for current protection.

The myth that fast-acting breakers are what you need to protect modern electronics is perpetuated on a daily basis in forums, including the FaceBook groups.

Transient Voltage Suppression is what is really needed. Breakers & fuses are to protect the transformer & wiring from too much current, TVS diodes are to clamp over-voltage, regardless of the age of the transformer, 100 years old or two weeks old. The damage from voltage spikes is ongoing and cumulative, and is just due to the nature of moving an electrical appliance(the train) along the rails it gets its power from. A faster breaker will cut power from a short sooner, but the damage is already done, and is continuing at all current levels below that which will trip a breaker.

Postwar transformers here and all have TVS diodes, simple and easy to install also.

While that is true about voltage spike and I agree 100%, when a locomotive is derailed and shorting, a PW ZW will continue to supply current through the shorted engines wiring and in many cases the circuit board. A fast acting fuse will protect that situation by acting. 

I stand by my statement but would add that a TVS would also be advisable. 

@MartyE posted:

...when a locomotive is derailed and shorting, a PW ZW will continue to supply current through the shorted engines wiring and in many cases the circuit board. A fast acting fuse will protect that situation by acting.

How is this possible if the short is on the track... literally shorting the circuit and blocking the current from getting to the locomotive? Unless, like, as I was told recently about MTH engines that had a design defect that routed center rail power between rollers across a trace on the circuit board.

Thank you for all the helpful answers. I can claim no expertise in electronics, even though I went through the Navy's electronic warfare school (but that was almost 40 years ago). My biggest takeaway from all the replies is that the Legacy base should be fine as is, but the locomotives are susceptible to damage, even accumulated damage over a period of time. The TVS diodes approach makes the most sense. Some quick research shows that there are scads of TVS diodes available in all kinds of ratings.

So what type do I specifically need for adequate protection? 

And would someone be so kind as to post a simple schematic for proper installation?

The information from ADCX Rob leads me to suspect that many of the issues model railroaders are having with "modern day" circuit board electronics could be directly related to cumulative damage from spikes. Kind of like heart disease, but electronic rather than biological. 

@ADCX Rob posted:

How is this possible if the short is on the track... literally shorting the circuit and blocking the current from getting to the locomotive? Unless, like, as I was told recently about MTH engines that had a design defect that routed center rail power between rollers across a trace on the circuit board.

Well there you have it. My PWC F3s do use a circuit board to connect the rollers. Ask me how I know. And you notice I did say wiring as well which also with a PW ZW can melt under the high current draw when a short occurs between trucks. 

@MartyE posted:

I also suspect that the drops may not help much. Depending on what you are running, with smoke units and lights you may be reaching the limit of the older transformer or maybe run the switches from another transformer.

About 90% of the drops were connected today (the bus line had already been run) and the good news is that there's virtually no voltage drop at any spot around the layout.

@BruceG posted:

...The TVS diodes approach makes the most sense. Some quick research shows that there are scads of TVS diodes available in all kinds of ratings.

So what type do I specifically need for adequate protection?

Check this discussion.

@BruceG posted:

... suspect that many of the issues model railroaders are having with "modern day" circuit board electronics could be directly related to cumulative damage from spikes. Kind of like heart disease, but electronic rather than biological. 

Yes, heart disease, & especially like hearing loss.

@MartyE posted:

Well there you have it. My PWC F3s do use a circuit board to connect the rollers. Ask me how I know. And you notice I did say wiring as well which also with a PW ZW can melt under the high current draw when a short occurs between trucks. 

Yes, a really big issue with the Polar Express cars as well. These are mechanical issues/defects, though.

@ADCX Rob posted:

Yes, a really big issue with the Polar Express cars as well. These are mechanical issues/defects, though.

I think we are on the same page. Results are still damaged engine. 

I strongly recommend fast acting circuit breakers in addition to the TVS protection diodes. I've repaired quite a few locomotives and passenger cars that had cooked interior wiring from a roller landing on an outside rail during a derailment.  I agree with Rob that fast acting circuit breakers don't protect against voltage transients, but that's not the only risk our poor trains face during a derailment.  I'm also an advocate for TVS protection diodes on the transformer feed to the track.

If you're also running MTH DCS, there's additional stuff we might discuss.

I believe this is the circuit board that fried on me when the front roller shorted to the outside rail and I was using a PW ZW.   Both front and rear roller use this as a buss point.  

K-Line was somewhat infamous for running power through traces on the motherboards, I've repaired a number of them.  TAS had that issues as well, they moved the power connection to the bridge rectifiers on their motherboard to avoid the small traces.

In order to carry 10 amps through a PCB trace with 1 ounce copper, the trace has to be 7.9mm wide, in other words, over 1/3" wide!  If you go to 2 ounce copper, you still need about 4mm of trace width.  If you look at any of the motherboards that have track power to multiple connectors, I don't recall any that have close to that size traces.

@BruceG posted:

The TVS diodes approach makes the most sense. Some quick research shows that there are scads of TVS diodes available in all kinds of ratings.

So what type do I specifically need for adequate protection? 

These are the TVS diodes that I use.  They have been recommended on the forum before.

Mouser: 1.5KE36CA

Digi-Key: 1-5KE36CA