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Hello everyone,

I'm building my layout and using four Gargraves turnouts to create a double crossover. My turnouts are diverging route to diverging route. I have them wired to one controller since they will both need to be in the turn position at the same time. The same for the other two. They are wired for non-derailing and operate fine. The problem is when one  train approaches the turnouts on the inner loop needing to use the non-derail feature. Only one turnout changes the position of the points now leaving me with two turnouts on one controller but turned in opposite directions. I thought I could run a wire from the non-derail wire of each turnout together since they would both throw to the same position but when I do this they will not throw to the diverging route, the non-derail feature throws them back to the straight through position leaving me with no way to enter or exit the inner loop. The switch motors are DZ 2500. They have green and yellow wires to the control rails one for each position. I'm only using the yellow wire to the isolated rails because I only need them to turn to the straight through position. Any suggestions would be appreciated. Thank you in advance for your replies.


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From what you wrote in your post the description is correct. The two isolated rails to control through are wired to the two yellow wires from each 2500. The green wires are unused.

First thing I would check is the yellow wire on the 2500 that’s not responding correctly is actually making contact with the other three wires. Maybe it’s just a bad connection.

Step 2 - I would check the 2500 that’s not responding. Isolate yellow wire, set the switch to diverge manually, and touch the yellow wire to the common to see if the auto derail sets the switch back to through.

If step two passes the Problem has to be in the isolated rails or the wiring so you would need to double check all of that.

If step two fails, the problem is with the 2500. Follow the instructions for the programming of the 2500 at the Z Stuff web site. It could be a defective 2500.

Good luck

If derail of all 4 switches works correctly, the I don't believe its the DZ2500s.

EDIT: Before you break out the voltmeter, you can not hook all 4 yellow wires together! You can only connect the two yellow wires from the two switches that make one path thru your crossover, and then connect the remaining two wires from the switches in the other path thru your crossover.

Crossover Derail

If you have a voltmeter, I would disconnect the yellow wires from each other. Get the switches in their thru positions. Use the voltmeter on DC to measure the voltage of each yellow wire to DZ2500's ground (which should be the same as your track's outer rail grounds, and the outer rails of both loops should be connected together except for the isolated rail sections). The DC voltage you should see is about 0.9V If you see 0V, then the wire is being grounded by something, and it shouldn't be until the train makes the circuit from non-isolated rail to isolated rail.

If you get the 0.9V reading on all 4 yellow wires, will have to think of the next step.

You might find this pic useful in your future uses of the DZ2500

DZ2500 Derail Operation Characteristics


Images (2)
  • Crossover Derail
  • DZ2500 Derail Operation Characteristics
Last edited by MED


Thank you for the suggestions. I'm not trying to wire all four turnouts together, only the two connected together. I do get 0.95 volts when checked with a volt meter. All the isolated rails check out fine. They all work fine individually including the non-derailing. I'm trying to get each pair to throw the same direction when the non-derail feature is used. I can tie one pair of turnouts together and get the desired result I'm looking for. This works for either pair. But when I  tie one pair together and the other pair together separately the turnouts only stay in the straight through position. I can throw the turnouts to the divergent routes but they immediately throw back to the straight position. Maybe this diagram can help explain my problem.


Images (1)
  • IMG_4030

You need 4 diodes, two for each pair of switches. Both pair of switches will be wired identically.

Here is the circuit for one pair of switches.

DZ2500 Diode Derail Two Switches

The Diodes allow the Isolated Rails to ground both switches Yellow Wires as a train passes on either loop. But, importantly, the Diodes prevent the state of the Yellow Wire of one switch in the pair from grounding the Yellow Wire of the other switch.

In your present situation, if you tie the Yellow Wires of the paired switches together, when you throw one switch to divert, its Yellow wire wants to go High, but the other switch still being in thru, its Yellow Wire is at Low Voltage, pulling the diverted switches Yellow wire low, forcing the diverted switch back to thru. The two Diodes prevent each Yellow wire from pulling the other switches Yellow wire low === only allowing the Isolated rails to pull the Yellow Wires Low to go back to thru position.

BTW - If you connected a Momentary Contact Switch between 1) the wire connecting Isolated Rails and Diodes and 2) track ground, then depressing this Momentary Contact Switch would also force both switches to thru, just like the Isolated Rails.

EDIT: BTW -  If you are the inquisitive type and want to demonstrate the DZ2500s' operation that is giving you the problem, before you wire my suggested solution, have the two Yellow wires disconnected from each other. Set one switch of the pair to Thru, the other switch to Divert. Using your voltmeter on DC, measure the Thru switch Yellow wire and see the 0.9V. Measure the Diverted switch Yellow wire, and see that it is at 5V. Now if you jumper the two Yellow wires together, the Thru switch's 0.9V will pull down the Diverted switch's 5V, causing the Diverted switch to go to its Thru state. As stated earlier, the Diodes prevent this interaction.


Images (1)
  • DZ2500 Diode Derail Two Switches
Last edited by MED

There will be very little current flowing thru the Diode, so a current rating of 100ma or more is more than ample. I use 1N914 diodes and have the overkill 1N4001 just because I needed a diode and it was what I had on hand at the moment.

The two diodes I mentioned are available in axial lead packages which is what I use and this package is depicted in the drawing below.

Diode Physicla and Schematic

BTW - I mention the following for your consideration so that when you obtain diodes, you may want to buy enough to cover you whole layout. Z-Stuff for Trains recommends a diode be placed between each the DZ2500's derail wires and the isolated rails. So you go DZ2500 Yellow wire to unbanded end of diode, then from banded end of diode to isolated rail - just like you will do for your crossover. Repeat for the Red wire. This recommendation is to protect the DZ2500's inputs in the case of a derailment in which the derailing engine/car shorts the center rail to the isolated rail. The DZ2500 creates its +5VDC supply, and the components used in the DZ2500 can not tolerate having the center rail voltage as high as a possible +31V peak from the transformer. Don't worry how the +31 can be there, just know it can be there. The diode blocks the peak voltage from getting to the DZ2500's inputs. Note: you only would use diodes when using derail function to isolated rail.


Images (1)
  • Diode Physicla and Schematic

Thank you again for your help. I do have another area with the same configuration of turnouts which I haven't gotten to yet so I will need diodes. I just ordered 100 diodes from DigiKey for $4.78 + shipping. I don't know when they'll arrive and I'll be away this coming week so I won't be working on the railroad for a while. When I do get back to my layout I'll let you know how I made out. Thanks again for your help.


Hello again, I finally got back to the turnouts. I installed the diodes. Everything works fine until a train needs to use the non-derail feature. All the turnouts return to the straight thru position. Also when a train is on the inner loop I cannot throw the turnout to the divergent route. As the train crosses onto the isolated rails the turnouts return to straight through, there is no way to exit the inner loop. Any other suggestions? I've checked and rechecked my wiring and  isolated rails several times.


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