DCC/DC circuit breakers

We are about to wire a club layout which will be both DCC and DC - either all DCC or all DC, never mixed - using DC block wiring. Is there a circuit breaker which will operate for both DCC and DC so that the layout could be divided into power districts? If there is, it would need to operate at a faster speed than the circuit breaker in a NCE booster so that, should a short occur, only one district shuts down.

It would be desirable that the circuit breaker incorporated a switch so that a power district could be turned off when work is to be done in one district.

Any suggestions?

Santa

There are no dumb questions, just inappropriate times to ask them ;~)

How about using an 1156 tail light bulb in series with each block. I think they are good for around 2 amps. If you need more power to a block I suppose you could use two in parrallel.

I am not sure if this is the exact answer to your question. My large HO layout is DCC and is divided into 13 districts. Each district is protected by Tony’s Train Exchange Power Shield. In the event of a short in the district, the Power Shield shuts down the district in 10 milliseconds and remains shut down until the short is corrected. You can wire an LED from the Power Shield to a panel to show the status of the district. If you wish to shut down the district and work on it, put a jumper between two rails. More elegant, but with the same result is to have an on/off switch on the panel.

Hope this helps on the DCC part.

Steve B.

I looked into this myself recently and don’t know of any single unit that will protect in both modes. However, it would seem to me that you could connect a DCC circuit breaker in series with an automotive fuse. The former would trigger instantly on a short in DCC mode. When running DC, the DCC circuit breaker would not react to a short but the fuse would.

John Timm

But you might not be able to pass DC through the DCC breaker. If you are using a DPDT or SPDT toggel switch for switching between DC and DCC an option would be to tie the track to the center lug. The tie one lug through a DCC breaker to the booster and then tie the other lug through a fuse and to the DC source. I don’t know of a cheaper solution other than the lightbulb, that was proposed previously.

Setup 1: Maybe I’m missing something, or am just plain ignorant. Any of the DCC breakers should shut down very quickly on a short circuit regardless of whether it is DCC or DC passing through it. The only possible exception would be if the current capacity of the DC power pack was insufficient to trip the DCC breaker. And this is going to be the key to any circuit protection that is common to both systems - the DC power pack connected to the block must have enough capacity to trip the same breaker when a short occurs in DC mode.

The 1156 bulb idea is a current limiter, not a circuit breaker, that limits current in the block to about 2 amps. Again, if each DC power pack doesn’t provide 2 amps, and can’t tolerate a 2 amp steady draw, there is no protection or limiting in DC mode. I’m sorry, I’m just not a fan of 2 amps flowing through derailed or shorting wheels.

The above assumes each DC block will also be a DCC power district, and each block/district equipped with its own breaker. This would likely be quite spendy.

Setup 2: Groups of DC blocks are assigned to a given power district. This likely means multiple switches to switch from DC to DCC mode. You would have to gang all the power districts on a switch with 2 poles for each power district to do it with a single switch. This has a lot of potential for operator error - not all mode switches get thrown and layout ends up in a combination of DC and DCC.

In this scheme, each power district/power pack has its own independent circuit breaker protection, upstream of the mode switches.

Setup 3: Use a single power district and traditional DC block wiring. Uses a single DC/DCC mode switch. Again, independent circuit protection is used upstream of the mode switch.

The obvious question becomes is it really worth hanging on to a full-blown

I have a DCC setup that allows you to run BOTH DCC and DC on the rails at the same time. Sort of DCC on top of DC. Works ok. I can have 9 DCC engines and 1 DC, each with their own thottle. I CAN run more than one DC engine, but both will be on the same throttle. Its just the inexpensive Bachman system. No brainer to use and does the job for me. I am sure there are other DCC systems out there that do this.

"Setup 1: Maybe I’m missing something, or am just plain ignorant. Any of the DCC breakers should shut down very quickly on a short circuit regardless of whether it is DCC or DC passing through it. The only possible exception would be if the current capacity of the DC power pack was insufficient to trip the DCC breaker. And this is going to be the key to any circuit protection that is common to both systems - the DC power pack connected to the block must have enough capacity to trip the same breaker when a short occurs in DC mode."

Good points. I agree that a circuit breaker probably would trip on DC or DCC, however, it is somewhat likely the current required to trip the CB on DCC would be a different value than on DC. I would call somone like Tony’ s Train Exchange and run the question by them, or get the right high frequency test equipment and test it out.

"The 1156 bulb idea is a current limiter, not a circuit breaker, that limits current in the block to about 2 amps. Again, if each DC power pack doesn’t provide 2 amps, and can’t tolerate a 2 amp steady draw, there is no protection or limiting in DC mode. I’m sorry, I’m just not a fan of 2 amps flowing through derailed or shorting wheels. "

I agree the 1156 bulb is a current limiter and not a circuit breaker, but it also gives a nice visual indication of the general location of the short on the layout. A lamp has the rather unique characteristic of presenting a low resistance when not lit, and increasing it’s resistance when a short occurs and the filament gets hot enough to light up. This is the reason it makes such a good variable resistance current limiter. In my opinion it is quite safe since all of your drop feeders should be capable of safely carrying 2 amps.

As with any

My not liking the 1156 bulbs as current limiters comes from the cause of short circuits, not the capability of the wiring. Once a layout is wired and debugged, just about all short circuits will come from derailments or metal wheels contacting a grounded frame on rolling stock. The approximate 2 amps - limited by the bulb - continues to flow until the short is cleared or the circuit is interrupted. This 2 amps is flowing through the derailed wheels and other components bridging the track. 2 amps is not likely to melt anything, but it may create some arcing and sparking. I personally would rather see the power shut down upon short circuit detection with an indicator light showing the district shut down.