Hookup up TIU

I would connect grounds together, after properly phasing the locos, by tying all grounds together on the TIU output side.  During operation, they'll be tired out on the layout anyway.

I don't see any benefit of tying the grounds together on the input.  Personally, I don't lie to have multiple paths, since under certain conditions, such as a bad connection at or inside the TIU, more current could flow through one TIU ground circuit than others, causing that circuit to overheat.

To illustrate:  Transformer #1 is feeding 10 amps through FIXED 1.  Transformer #2 is feeding 10 amps through FIXED 2.  If the grounds are tied together on the INPUT side, and for some reason the ground connection for FIXED 2 becomes poor inside the TIU---say the terminal post gets loose---, the resistance in that circuit will be higher, so more (perhaps all if the connection fails) the ground current of transformer #2 will pass through the FIXED 1 ground circuit, and then proceed to transformer #2 through the input side tie-in.

Var,

   RJR is giving you the correct skinny, he knows his stuff, might want to take his advise to heart and use it.

PCRR/Dave

Not sure what you mean by "phasing the locos". If you mean phasing the transformers, I presume they should already be properly phased since both are modern units with three prong plugs. I can easily check the phasing between the transformers using a voltmeter; will do so just for belt and suspenders. Anyway,per your recommendation, we will only tie the grounds on the output of the TIU. Thanks, Var

Sorry for the typos.  Yes, I mean transformers.

Phasing cannot be presumed.  There have been differences among same make & model.  In most model train transformers, the is no electrical reason for connecting either end of primary coil to either hot or ground, so makers may vary their approach.

Interesting insight re phasing not necessarily automatic with modern units using three prong plugs. In the old days, if two transformers were out of phase, all you had to do was reverse the plug on one of them. How do you fix the problem now; the only idea that comes to mind is to use a ground "cheater" and reverse the plug on one of the new transformers. That seems like a safety hazard to me; what alternative would you suggest (I guess you could swap the hot and ground outputs from one of the transformers)?  Thanks, Var

In the case of a postwar Lionel transformer, I doubt it would be a safety hazard, since the ones I've seen simply have the 2 conductors tied to the ends of the primary coil, with no switches or other devices that should be cutting the hot.

On these, one solution is PROBABLY just go in and reverse the wires on the primary.  A simpler solution would be to replace the plug, but if there is a 3rd conductor, be sure to keep it on the long prong.  I waffle the answer because I haven't seen the inside of every transformer.

Be sure to use an ohmmeter and make sure neither of the conductors is connetced to the case or to the prong.  If you get any reading but infinity, there is an electrical problem.

I have two Z4000 and recently replaced one of the Z4000 with a new ZW-L.  Both the Z4000 & ZW-L have polarized plugs, and when I connect both transformers into the same power strip, there is a voltage reading of approximately 20v between the two hot terminals of the Z4000 & ZW-L, indicating they are out of phase. When I manage to reverse the plug on the ZW-L, the there is no voltage difference between the hot terminals of the two transformers.   Am I making the wrong assumption that with polarized plugs, the transformers should automatically be in phase with one another.  Has anyone run into this condition before and does anybody have a wiring schematic for the ZW-L.

rad400, your assumption is not correct.  See my post just above yours.

I worked on the hookup today and indeed, the MTH Z4000 and the new Lionel ZW were out of phase.  Turns out the ZW just has a polarized plug. I took a three prong plug cheater (i.e., to hook a three prong plug in an ungrounded outlet), reversed the polarity at the outlet, and problem solved. Thanks to RJR for making the point not to assume anything about transformer phasing. By the way, the club layout is now good to go

Var,

   Mark the plug so you know how to plug the transformer in, keeps from having to test transformers each time you set up your Christmas layout.  Also remember if you are running DCS to place the Scott 10 Amp resettable breakers between the TIU & the old ZW, or KW transformers, they both have slow blowing internal breakers, that will let the TIU become damaged. 

PCRR/Dave