adding a Lionel KW to a layout that has a mth 4000

"I checked for polarity by attached a wire from my KW U post to a black lead from my Mth 4000, with a meter I'm getting 17 volts with both transformers on. So I am assuming they are in Phase."

Transformers that are correctly wired in phase will indicate zero volts difference between their hot output terminals, when their common terminals are connected together and their hot outputs are set to equivalent voltages.  It's hard for me to understand exactly how you have them wired, but getting a reading of 17 volts between two hot outputs does not sound correct.

The output of transformers is A.C.  There is no "polarity" in A-C circuits. There is in D-C circuits. Not being familiar with some of the newer power supplies, could you tell me if any of the outputs you are using supply D.C.?

I think I'm using the word polarity wrong. Should the attachment the black lead be less than 17 volts?

@leeg posted:

I think I'm using the word polarity wrong. Should the attachment the black lead be less than 17 volts?

If the two voltages are set at approximately the same setting, the difference should be close to 0 volts.

Thank you, I tried reversing the plug on the second transformers still getting the same bad results. Maybe the second TIU is bad. Haven't been able to figure it out yet.

Assuming the transformers are phased correctly, my understanding is that when you have a layout powered by more than one TIU, you can experience control issues when you try to run an engine that was "programmed" by or into one TIU and then trying to operate that engine on trackage controlled by the second (or third, fourth, etc.) TIU.

I don't know for sure if that is your issue, but if it is, the solution is to set both TIU's to operate in Super TIU Mode.   

That does seem like one of the major issues. I will have to read up on Super TIU Mode. Right now my main TIU is labeled 1, and my other TIU is labeled 2 on the DCS.