Circuit breakers to protect tracks?

[Bob]

Since my Cumberland Subdivision has been functional, I have managed to burn out 3 locomotives - two derailed going through an incorrectly lined turnout (my bad) and by the time I noticed, they were toast.  I have an NCE system and I think a 2 amp power system.  Does anyone place a circuit breaker in-line so that if the tracks are shorted out the breaker is thrown before damage is done to an expensive locomotive?  I know I should pay more attention, but when operating solo I love to have several trains running at a time, so a derailment might occur without me noticing for a while.

[djconway]

Start by checking your current wiring. All DCC systems have a built in over load / short circuit protection. 
Its simple to test, create a short at locations around the layout, if the breaker does not trip immediately your wiring may be under sized.

There are several solutions if you find areas where the internal breaker doesn't trip.
1-replace your existing bus wires 14 gauge in place of 16
2-make sure your feeders are lree than 12" also drop feeders every 36 to 42 inches
3-use something like the Digitrax PM 42 to break the layout into up to 4 zones each

[narrowminded]

Using a light bulb for overload protection.   https://www.therailwire.net/forum/index.php?topic=42404.0

If you read the whole thread the subject is covered pretty well, including what to really use.

[Bob]

Thanks guys - I really appreciate the information!

[djconway]

 You can't have too many feeders
Always go 1 or 2 sizes heaver than you think you need for the bus wiring

[robert3985]

You can't have too many feeders
Always go 1 or 2 sizes heaver than you think you need for the bus wiring

Welll...one feeder for every piece of rail is just about right.  Ya don't need more than one feeder per piece of rail...which WOULD be "too many".

Main power buses benefit from a few things in addition to "heaviness", such as the purity of the copper and how many strands there are.  Using cheap wire for your main DCC power buses is just looking for problems.

Truth is, main power buses conduct more than just electricity when used for DCC, and signal loss can be a problem.  Although you'll gain less electrical resistance by going to a bigger gauge of high-purity, fine-stranded wire, there is a school of thought out there that 14 gauge wire is ideal for carrying DCC signals...and equal-quality 12AWG cable experiences significantly more signal loss, even though its electrical resistance is significantly less.  Go figure.

With that in mind, when re-wiring my DC-only layout to modern DCC standards, I relied on Ntrak's DCC standards largely because of their success running super-large modular layouts, and my modular/sectional layout is in a constant state of growth...so I went with 12AWG high-purity-copper black/red zip speaker wire for my main power buses.  I experience zero signal loss problems even when paired up at shows with my partner's section, forming a 45'X38' double track mainline layout.

After burning up one of my Kato F-units...actually it was just one truck that melted...on the local non-Ntrak club's modular DCC layout (NCE Wireless DCC) caused by a bad turnout, I decided I'd better get some shorting protection for my own modular/sectional layout. 

Having bitten the bullet and wired a 6" 22AWG solid copper feeder to every blinkin' piece of rail on my layout, I divided it into three districts...east bound mainline, west bound mainline, and yard/Park City Branch using a Digitrax PM42 Quad Power Manager, reserving one district for my 90' turntable at Echo using the auto reversing feature. 

During a show, if one of my guest operators runs a switch or does something that causes a short, only the one district he is in will stop and reset, keeping the two other districts at full power...operating without pause...and not cooking any shorted engine on the district having the problem....and alerting me and other operators that there is a problem on a particular district because all the other engines in that district are stopped.

Although a lot of negative stuff has been written about Digitrax's PM42, it has worked perfectly for me for years.

Photo (1) - My portable DCC power-board, with PM42 mounted vertically and 12AWG high-quality zip-wire power buses connecting to the layout:


Cheerio!
Bob Gilmore

[peteski]

Since my Cumberland Subdivision has been functional, I have managed to burn out 3 locomotives - two derailed going through an incorrectly lined turnout (my bad) and by the time I noticed, they were toast.  I have an NCE system and I think a 2 amp power system.  Does anyone place a circuit breaker in-line so that if the tracks are shorted out the breaker is thrown before damage is done to an expensive locomotive?  I know I should pay more attention, but when operating solo I love to have several trains running at a time, so a derailment might occur without me noticing for a while.

What exactly does "blown  up" mean?  Were wires melted inside the model? Truck electric pickup plates melting the plastic frame?  Damage to the decoder?  Anything else?

Most (or probably all) DCC booster have fast acting electronic circuit breakers which will shut down then the current being drawn exceeds the set limit.  If the total resistance  of the "short" (which includes the track and all the wire between the track and the booster) is high enough not to exceed the tripping current, then the current permitted by the "short's" resistance will continule flowing, possibly heating up some delicate component of the "short".

Adding a series-connected light bulb "circuit protector" into the DCC bus might not prevent the damage.  First of all, since the cold filament of the bulb is very low, if a "short" occurs, there will be a current (and voltage) spike still produced (which could scramble the decoder's programing). Also, the the bulb's operating current is fairly high, then the "shorted" current can still damage some delicate part of the locomotive. Things like a 30AWG track pickup wire inside the loco might still melt.

[Dave V]

Following...  I know guys who swear by circuit breakers and our modular club layout has one with its NCE system.

However, my Digitrax system--one I've been using now for 13 years--has adequate automatic short protection.  Now, I rarely run more than 2 locos at a time, but I'm really trying to imagine a scenario where I would need more protection than that which the booster already provides.

[nkalanaga]

The light bulb will prevent mechanical damage to the locomotive.  Like Peteski said, it will not prevent spikes from damaging the decoder.

The reason the light bulb is a better choice than a power supply circuit breaker is that it's cheap enough to use in each block.  With enough feeders, it's unlikely that one will ever have need for more than an amp in a given electric block, which shouldn't damage the locomotives.

The power supply, especially in DCC, can provide a lot more than one amp.  Its circuit breaker has to be able to allow at least the rated current, which can easily be enough to melt wheel insulation, truck frames, and other plastic parts, when something shorts.

The ideal system combines the two.  The circuit breaker protects the power supply and main wiring against large shorts, while the individual light bulbs protect locomotives, rolling stock, and turnouts.  The bulbs are cheap enough that one can literally be put in every feeder.

[peteski]

The light bulb will prevent mechanical damage to the locomotive.  Like Peteski said, it will not prevent spikes from damaging the decoder.

As I mentioned in my post, improperly chosen bulb will not protect delicate wires or pickup strips from heating up and melting surrounding plastic. If a short causes the bulb to glow brightly, if the bulb is rated at couple of Amps, then that can be enough current, if allowed to flow for several  second,  to heat up those delicate metal components in N scale locos.  Remember that the bulb is in-series with the rest of the circuit, so the current flowing through the entire circuit is the same as what is flowing through the bulb.  The "bulb circuit breaker" is really more of a way to protect the power source (booster or DC throttle) from over-current, rather than protecting whatever is causing the short.  If a smaller wattage (smaller current) bulb is chosen, its filament might start to heat up, even under normal current consumption, causing voltage drop at the bulb, affecting the loco's performance.

[nkalanaga]

True, the bulb will have to be chosen carefully. 

I don't use DCC, but do use the light bulb current limiters on my lighting circuit.  The power supply is a surplus-store 25 amp bench supply, so the circuit breaker isn't much use for local shorts.  I have a light bulb in series with every terminal strip, about a dozen around the layout, and I have seen the bulbs glow a few times.  The usual culprit is when I throw the one turnout equipped with a screw-motor switch machine, which is on its own terminal.  It almost exceeds the bulb's rating.

The main accessory bus is a piece of house wiring cable - #14 copper.  I'm not worried about it overloading.

[mrp]

Try one of the circuit breakers made by DCC specialties.
https://tonystrains.com/store/dcc-sound-power/dcc-circuit-breakers-slash-auto-reversers/dcc_specialties

[Ron McF]

I'm really trying to imagine a scenario where I would need more protection than that which the booster already provides.

If you're operating solo then you'll probably never need any more protection. But if you're operating with 8+ other guys, then you may very quickly grow tired of short-circuits shutting down the whole layout.

If you're going to use auto-lamps for short-circuit protection then use a combined stop/tail lamp in conjunction with a PTC fuse, as described here:
http://www.rr-cirkits.com/Notebook/short.html

According to the author, the PTC fuse allows "the full 2.1 amps of the stop filament, plus the 0.4 amps of the taillight filament, to flow for about 30-45 seconds before opening the circuit. Once the PTC unit opens the stop filament circuit, then only the 0.4 amp tail light element glows. This still provides an indication of the short circuit location, but drops the current to a safe value until the short is completely removed."

Regards,

[up1950s]

What about a 12 volt or so grain of wheat lamp in series on one leg of the feed within each loco . You could paint it black . Would that frig up the DCC , I don't think so . This might protect each loco and be more sensitive that a power supply output CB , though that is also needed .

[Ed Kapuscinski]

Following...  I know guys who swear by circuit breakers and our modular club layout has one with its NCE system.

However, my Digitrax system--one I've been using now for 13 years--has adequate automatic short protection.  Now, I rarely run more than 2 locos at a time, but I'm really trying to imagine a scenario where I would need more protection than that which the booster already provides.

In my experience it's been so that a short on one side of the layout doesn't shut down the WHOLE layout. I had one breaker setup for the yard and one setup where there was some switching. I figured that if there's gonna be a short due to a switch or something, itd be there.