circuit breaker location

The consensus here on the forum is to locate breakers between the TIU Outputs and the track connections.  An instant type is mostly preferred like the Airpax or PSX-AC.

Here is a link to another thread discussing this ogrforum: TIUs and Circuit Breakers

EDIT: Although if using postwar transformers, Circuit breakers on each output are also highly recommended.

@SteveH posted:

The consensus here on the forum is to locate breakers between the TIU Outputs and the track connections.

NO, sorry, that is incorrect.

Breakers and fuses should be nearest the power source- the transformer BEFORE the TIU.

PSX-AC specifically before the TIU not after because it could interfere with DCS signal.

Another reason is, the TIU itself is an electronic "load" and has TVS devices on each output that can fail shorted. And while the TIU has internal fuses on each channel, they are large 20A rating, so when/if a TVS is damaged and fails shorted- you don't want the TIU taking that brunt of the current until the 20A fuse blows.

Drawing originally by @CAPPilot but some details edited by me for fuses or breaker placement.

@Vernon Barry posted:

NO, sorry, that is incorrect.

Breakers and fuses should be nearest the power source- the transformer BEFORE the TIU.

PSX-AC specifically before the TIU not after because it could interfere with DCS signal.

Sorry Vernon but I disagree with your conclusion.

Breakers and fuses can be anywhere along a power feed, specifically because they monitor current through a wire, and thus the entire path, unlike voltage which is measured across two wires.

As a result anywhere along the path of the feed circuit between source and load is fine.  The breaker or fuse opens the entire length when it trips, regardless of its position.

The PSX-AC is a special case because it requires at 10VAC on its input in order to operate.  For this Vernon you're quite correct.

Mike

Fine to disagree but I stated the reason.

The breaker is there to protect as equipment much as possible. The way to do that is put at the source. Then it protects your wiring, the TIU, more wiring to the track, and so on. This is a basic electrical convention. Even modern recent autos are putting fuses right in the battery terminal these days for this reason.

And, given the cost of TIUs these days, you'd think you would want to provide as much protection against all faults as possible.

Would there be an advantage to installing a pair of instant breakers like the Airpax, one at the TIU Hot input (red) and another at the TIU common output (black)?

My thinking for the one at the input side is in line with protecting the TIU electronics as Vernon and Mike have mentioned.  The one at the output would be for a different scenario, not yet mentioned in this thread.  There could be an unexpected source of power somewhere on the layout that could back feed current into the common return to the TIU.  This second breaker on the TIU common output would provide protection in this case.

@SteveH posted:

Would there be an advantage to installing a pair of instant breakers like the Airpax, one at the TIU Hot input (red) and another at the TIU common output (black)?

My thinking for the one at the input side is in line with protecting the TIU electronics as Vernon and Mike have mentioned.  The one at the output would be for a different scenario, not yet mentioned in this thread.  There could be an unexpected source of power somewhere on the layout that could back feed current into the common return to the TIU.  This second breaker on the TIU common output would provide protection in this case.

I'm trying to play this scenario but IMO opening the common for any reason just invokes far too many problems. House wiring is similar- you never want an open neutral (AKA Common). In theory, an open Common causes just such differential voltages. Ideally, just have a breaker in every power source (example- aux power terminals).

Vernon, I agree that each power source's hot output should have its own breaker.

I also agree with not opening the common in house wiring where the neutral should be at or very close to earth ground potential, GFCI and AFCI protections rely on a solid neutral and /or ground connections and there are potentially dangerous 120 and 240 volt sources present.

Train circuits are supposed to be isolated from the house wiring via inductive/magnetic coupling in the transformers' secondaries.  House wiring should also only be done by a qualified electrician.  So, maybe house wiring is an apples and oranges comparison to train wiring.

As you know, many postwar transformers do have breakers that disconnect the common when tripped.  Although this isn't as good as individual breakers on the hot side outs, I'm not aware of tripped breakers on the common causing issues (EDIT: when supplemented by instant breakers on the Hot outputs), other then being too slow for modern electronics.

Since many model railroad enthusiasts don't have a firm grasp on signal flow, my thinking is that a belt and suspenders approach of breakers on the hot of every power source; and for an added measure of protection against the possibility of an unforeseen back fed power source, TIU outs/ common return breakers would be better than not having that common side protection for the TIU.  Especially considering the now scarcity of TIUs.

@SteveH posted:

As you know, many postwar transformers do have breakers that disconnect the common when tripped.  Although this isn't as good as individual breakers on the hot side outs, I'm not aware of tripped breakers on the common causing issues, other then being too slow for modern electronics.

Actually, a major shortcoming of the single breaker in the common for a multi-output transformer is the total lack of protection for a short between two of the outputs!  There can be unlimited current in that case with no circuit protection at all.

@gunrunnerjohn posted:

Actually, a major shortcoming of the single breaker in the common for a multi-output transformer is the total lack of protection for a short between two of the outputs!  There can be unlimited current in that case with no circuit protection at all.

John, where you've quoted me is taken out of context.  I've been advocating all along for installing instant breakers on every output of a postwar transformer.  This present discussion is about whether to also add a breaker to the TIU output common.  I've since edited the section you quoted to remove the ambiguity you've pointed out.

Well, I didn't see that in the reply, hence my clarification.

And with that, IMO "the rules":

#1 Ideally place breakers/fuses nearest the source (transformer or power supply) in the "hot" or red terminals output

#2 Place or ensure the source has breakers or fuses in each output (examples- each handle output, or accessory outputs)

#3 Do not place breakers or fuses in Common (black post- sometimes U) wiring- since most transformers share common and many folks wire layouts to depend on common for different voltages and activation of accessories. Ideally common should be your most robust wiring since it is shared and may be carrying return currents.

@Vernon Barry posted:

Fine to disagree but I stated the reason.

The breaker is there to protect as equipment much as possible. The way to do that is put at the source.

Vernon,

Your conclusion is correct for clamping voltage spikes, but not for stopping excessive current flow.  Why?  The current is interrupted through the entire path at essentially the same time (given the speed of electrons).  It's not interrupted near the source any quicker than the at the far end.

Therefore a traditional breaker or fuse can go anywhere along the path.  Everything in that path is protected simultaneously and to the same degree.

(Electronic breakers are a different story because they need to be powered in order to do their job.  Where that power comes from is important, but not with traditional fuses and breakers which need no external power to determine that excessive current is flowing.)

Mike

Just to clarify a minor point. The PSX-AC is a special case where it has both terminals but generally does adhere to the above 3 rules. The common through a PSX-AC is not broken, the "hot" is the one that breaks or opens, and thus it follows rule #3. Again, the black common lines straight through clear to the terminal blocks are not broken in the even of a current trip event.

Another great diagram originally by @CAPPilot and further edited by me.

@Mellow Hudson Mike posted:

Why?  The current is interrupted through the entire path at essentially the same time (given the speed of electrons).  It's not interrupted near the source any quicker than the at the far end.

Therefore a traditional breaker or fuse can go anywhere along the path.  Everything in that path is protected simultaneously and to the same degree.

(Electronic breakers are a different story because they need to be powered in order to do their job.  Where that power comes from is important, but not with traditional fuses and breakers which need no external power to determine that excessive current is flowing.)

Mike

The TIU is a 2 terminal device ACROSS the hot and common. It can short and fail internally as a short (most times the internal TVS shorting). A breaker/fuse after this will never detect that short.

I understand your thought process, but again, just like a switch- everything before the breaker/fuse is still connected- still live, still "hot". If that device has a return path and internal circuitry that can fail- the short bypasses the breaker completely.

And TIUs DO short on the outputs/inputs as a fault.

I am have an old TIU with no internal fuses. A Z1000 transformer,a 15amp circuit breaker from Scotts-Odds-n-Ends.I have not used DCS for 18 years, forgot alot. I bought a home 22 years ago with a big basement for my Trains. Finally starting my dream layout .Taking out my MTH emgines and all batterys  are dead except for a 765 Proto 1 I did a upgrade on.Made a big loop in my living room, hardwood central. trying to remember how to run DCS. Loving Retirement.

Vernon,

In the scenario where the 3rd-party breakers are between the TIU and track, and if a TVS in the TIU shorts, aren't the internal thermal breakers within the Z4000 sufficient to protect itself?

Ok, here's a real world possible scenario demonstrating what I mean:

Let's say the TIU's 2 Active channels are each being powered by an output from 2 different phased post war transformers, each capable of delivering >10 Amps.  Following best practices, the transformers' Commons are connected together and each transformer Hot output passes through an instant type breaker on its way to the TIU input.  So far so good, if either circuit's current exceeds 10 Amps its breaker trips.

Everything works fine until one day the (grandson/daughter, dog, cat or rodent) accidentally disconnects, chews through or otherwise interrupts one of the Common connections returning to only one of the TIU's outputs.  The next time the layout is powered up and significantly more than 10 Amps is drawn by the trains, puff magic smoke from the TIU.

~ 20 Amps of current would then be flowing through the one remaining TIU channel Common that's still connected.  If the TIU output Commons were also individually protected by 10 amps max instant breakers, this scenario could be prevented.

If the TIU's Common circuitry path can handle more than 10 amps (unclear), then all of this is a mute point.

@Vernon Barry posted:

The TIU is a 2 terminal device ACROSS the hot and common. It can short and fail internally as a short (most times the internal TVS shorting). A breaker/fuse after this will never detect that short.

I understand your thought process, but again, just like a switch- everything before the breaker/fuse is still connected- still live, still "hot". If that device has a return path and internal circuitry that can fail- the short bypasses the breaker completely.

And TIUs DO short on the outputs/inputs as a fault.

Agreed, but this is a unique situation because the TIU is not a simple electrical device.  There isn't a single path for current to flow through it.  There are two.  One through the TIU and the wires out to the train and back to the power source, and a separate one through the TIU's internal circuitry back to the power source.  I've been speaking about the particular path through the tracks and the train and not the other one.

If you want to protect against a short within the TIU put the breaker or fuse between the source and the TIU.  If only the train then between the TIU and the track is fine.

Mike

"As a result anywhere along the path of the feed circuit between source and load is fine.  The breaker or fuse opens the entire length when it trips, regardless of its position."

Nope. An open circuit breaker or fuse opens the circuit towards the load (downstream). It cannot open a wire behind it (upstream). The upstream feed wire is still energized.  This simple concept may not be applicable to the huge discussion above, but it's a fact of physics.

@Bruce Brown posted:

Vernon,

In the scenario where the 3rd-party breakers are between the TIU and track, and if a TVS in the TIU shorts, aren't the internal thermal breakers within the Z4000 sufficient to protect itself?

Given the current cost of TIUs, I say no. That's an opinion statement, by all means do a proper risk assessment. Likely hood of failure, cost of failure, cost of protection, likely hood protection mitigates the risk.

Yes, TIUs (later revisions I might add not the first revision) have 20A fuses. Problem though, beyond the high rating, you have to open up the TIU just to check or replace a fuse. And that's hoping it has them. Given that the market demand out there- a person might be stuck on an older TIU.

Just to be full circle and give as much information as I can. I've never ever tripped one of the 12A Z4000 track output channel breakers ever. I've seen my fair of shorts and derailments. Further, our local club uses 4 Z4000 for 8 tracks in total- so the sample size on that is a fair number of events and fair number of transformers. Further, the Z4000 overcurrent sensing on a channel allows for roughly 5 seconds or more of up to 12A displayed on the ammeter before it typically trips.

So if we want to go full scenario on my personal rules to live by:

If your regular every day train loads begin to creep up on 7.5A or higher for a given handle or channel, I would recommend passive mode for TIU. I can go into a whole thing about terminal connections with higher failure rates and so forth- both from trains and my 3D printer experience as well as even manufacturers of connectors and derating factors. My current home layout has cheap 5A rated thermal breakers between the Z4000 and TIU, the club layout has 7.5A thermal breakers, but more importantly runs the TIU completely passive mode (after the first time they melted the terminals on channel 2). Either way, there is a breaker between the Z4000 and TIU.

Again, my belief is- regular load of 5A or less, run TIUs through is fine- still need to ensure internal terminals are tight, still should have protection before the TIU between the source (transformer) and the TIU.

If you find yourself on a regular basis tripping that 5A breaker or exceeding the load with MU consists (lashups) or just lots of real current draw, and using a TIU, then I recommend passive mode. Passive mode does require inductors and more wiring, but the idea is no longer passing heavy current through the TIU. Yes, you lose Estop from a DCS remote cutting power, but that IMO has a whole other series of issues.

PASSIVE MODE TIU WIRING

This, combined with the other rules all fixes Steve's scenario.

Also, from  the risk assessment (lots of what I do in my day job) protection is only good if easy to use and doesn't result in the user bypassing it.

Example- fuses- relatively cheap, but if a user keeps blowing a fuse over and over, they tend to put in a higher rating to keep it from blowing.

Breakers- manual reset is best, but for the same reasons, users either cannot figure out why they don't have track power or eventually complain and bypass. Thus self resetting is a compromise. You still have protection, less than manual reset, but less anger from the user.

Again,  for the purist- a super fast instant trip manual reset breaker is the safest. However, imagine a club layout, or novice user needing to know each and every time to reset the breaker.

@nkptomo posted:

I am have an old TIU with no internal fuses. A Z1000 transformer,a 15amp circuit breaker from Scotts-Odds-n-Ends.I have not used DCS for 18 years, forgot alot. I bought a home 22 years ago with a big basement for my Trains. Finally starting my dream layout .Taking out my MTH emgines and all batterys  are dead except for a 765 Proto 1 I did a upgrade on.Made a big loop in my living room, hardwood central. trying to remember how to run DCS. Loving Retirement.

Given this scenario, I would run that TIU in passive mode.

Henning's happens to sell the exact 5A thermal self reset breaker I tend to use.

https://hennings-trains.shopli...circuit-breaker.html

Another member @zhubl makes a custom board with choke and other features just for this purpose sold under item number 385356672902

Otherwise, the DIY choke https://www.digikey.com/en/pro...P1770TA-220M/5429725

This post is also great with a huge information resource of common parts for power and filtering from Digikey and other electronics related to these topics https://ogrforum.com/...3#151914096433446323

I have an old TIU. no fuses. Z100 transformer.A Scotts 15 amp circuit breaker. Where do I put the breaker?

What is passive mode?

@nkptomo posted:

I have an old TIU. no fuses. Z100 transformer.A Scotts 15 amp circuit breaker. Where do I put the breaker?

Your Scotts 15A circuit breaker is NOT useful in the context of this situation. 15A rating it will never trip and never protect anything. Use it as a door stop, a paperweight, but nowhere with your trains.

Your power source, a Z100 (assuming you mean an MTH Z1000?) already has a 6A thermal circuit breaker in the side.

@nkptomo posted:

What is passive mode?

Passive mode is using the TIU to add the DCS signal to the power on the track rather than running the power through the TIU (power input terminal and out the power output terminal).

Since your TIU is known to be prone to burnout when overcurrent passes through it- this is a way to still use the TIU but not pass any current through it and lower the risk of damage.

Thanks,I was afraid of frying the TUI. I am going to try out  my MTH engines and see if they need new batterys.