For the sake of this discussion, please assume:

HOT lead = “A” terminal on my ZW = center rail on track

GROUND lead = “U” terminal on my ZW = outer rail on track

Things didn’t go as planned when I tried to wire my used-but-new-to-me ITAD to a Lionel PW 145 gateman. Long story made short, I discovered that the ITAD is internally wired such that the NO (Normally Open) relay contacts, when activated or closed, supply HOT voltage, not GROUND. This seems to be at odds with the “standard activation methodology” employed by many accessories of completing a ground, not providing HOT power.

To prove my point, I wired a lamp to the ITAD’s NO and COMMON terminals, and sure enough, when the ITAD was unblocked, the light was off – when blocked, the light turned on. I tried the same with the NC contact and COMMON – as expected the light was on when unblocked and off when blocked.

I have searched the MANY ITAD discussions on this forum and they all seem to allude to the NO terminal being switched to GROUND when activated – that is NOT what mine does. What am I missing? Is this the way it is supposed to be? I thought there might be a jumper to reverse the center relay contact from HOT to GROUND, but I don’t see one. And as noted elsewhere, MTH schematics are not to be found, and their documentation is sorely lacking on this sort of detail.

I would appreciate any insights...


Original Post

The ITAD has the NO, NC, and COM terminals to be connected to the accessory as needed. It would appear that connecting the load to the COM and the NO or NC , then NO or NC supplies HOT while COM is supplied all the time.


Why not swap "HOT" and "GROUND" wires powering the ITAD?  It's AC so the ITAD electronics does not know the difference.

Then, the COM output to your accessory will be "HOT" and the NO/NC outputs to your accessory will be "GROUND" thereby conforming to your "standard activation methodology".

OK, I tried swapping the A and U terminals as was suggested – no change.

For me, it's oft times easier to understand a schematic as opposed to reading a circuit description, so I drew the schematic for the PW 145 gateman and the ITAD, although the ITAD is more of a block diagram than a schematic – but it is a correct block diagram. The drawing in the lower right corner is straight from Lionel, where they were demonstrating how to use a 145c contactor to actuate the Gateman, I included it for clarification of my A, B, C terminal labeling.

ITAD to Gateman

It quickly became obvious what the solution was, and I wired things accordingly and it works just fine – the Gateman light stays on at all times and the Gateman pops out when the ITAD sensor is blocked.

I suspect that I simply did what you guys suggested, just took a roundabout way to get there. 

Thank you!!!!



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