Common Bus

Hi Ralph, The TPC 400 can handle 400w before it melts. However, the power is generated by a transformer & then passed through the TPC.   Meaning wattage of the transformer will determine the minimum wire gauge. The length of the feeders can also be a factor, but when we get to 14g length is not much of a factor. We would need to know exactly what transformers/power masters or whatever supplies the power you are using. Then we'd be more able to advise.

   I will say this, with a postwar ZW at full throttle I've never been able to melt a 14g wire. It may feel warm, but not even close to damaging it.

      On my layout most of my feeders are 16g, but some are 18g. At normal running volts of about 14-16 when the grandkids derail a train the circuit breaker opens the wire will feel warm, but still not hot. Even the 18g feeders, which feel hotter, but not near melting the insulation don't take damage. But... thinner like 22g will often smoke the insulation & burn things at normal track voltage. Again these are with a postwar ZW275. I've ran this layout for over 20yrs & dozens & dozens of circuit breaker openings. Still no damage.

    Sure 12g gives more protection, but I expect 14g would be fine. Again depends on your power source. TMCC/Legacy volts are higher so the wire could heat faster, but still my experiance you should be fine.

     Very best, Don Johnson

Thanks Don

I use 180 W PoHo on two and a PW ZW 275 on the other two - A handle on one and D handle on the other for the conventional feel. 

I was more concerned about the combined effect of the power, eg, if the 1 PoHo needs to be supplemented with another 180 Watt brick, am I asking for trouble or should I go for the 12 AWG now in the power center?

Ralph

I expect 14 gauge is okay but, as always, it depends on what the normal load will be on a particular circuit. Motors, car lighting, etc? What is the expected load on the power district [loop,oval,etc] the TPC is controlling?

#14 gauge will handle the output through a TPC 400 although I doubt you are planning to supply that much transformer power to a single power district. That[400 watts] is wheel gapping, rail welding power upon a derailment.

Okay, with your last posting,what appears to be 10 amps[180 watts] capacity per throttle/per district, #14 will work. #12 would give you a consistent circuit but with a short wire run to the Bus from the TPC/Transformers, you should be okay.[your pwZW is not going to supply more than 180-190 watts total, one or all throtles, even at a cool efficiency].

I agree that 14 gauge is probably OK.

Before we get any comments that "14 ga is rated at 15 amps, 12 ga is rated at 20 amps, etc.", let's review how wire is rated.

There are two important factors:

The first is how hot the wire gets with respect to the insulation's melting characteristics.  The amount of heating greatly depends upon how the wire is "packaged" - open bare wire, single insulated wire, Romex, multiple wires in conduit, etc.  If you have several wires together with the heat trapped around the wire, the rating must go down.  If you have easily-melted insulation, the rating must go down.  For many train applications, the wires are relatively open and loosely bundled.  (The use of wire trough may change this assumption.)  Our train wiring typically doesn't operate at peak power for extended periods of time, minimizing the longterm degradation of the insulation.

The other factor is how much voltage drop will result at maximum current.  A common standard for normal power wiring is that the drop for a long run should be no more that 2% at maximum load.  There is a table of maximum lengths for a 2% drop for various currents and wire sizes.  For your house wiring, 2% is about 2.5V, but that when you are starting with only 18V for our trains, that same voltage drop would be 13%!  This is why we need to run large wires for busses on large layouts.  (From that table, a 14ga wire can only have a 30 foot branch at 15 amps before the drop reaches 2% for a 120V circuit.  The branch has a total of 60 feet of wire.)

Remember that the length of the run will also determine the voltage drop.  While I don't agree that the PH should have the wimpy wire they use, if you run that wire 50-60 feet, you'll have a significant voltage drop!

Absolutely John!

Thanks for the replies. You have questions about what I am doing to appropriately provide guidance. Sometimes, a novice like myself doesn't know all the info to give to get the advice. My head is spinning, but I'll attempt to describe the endeavor.

Several months ago I decided to go to Legacy and add a few more blocks to my layout, add a bit more power and zip. That has me redoing wiring for my layout. At the same time, I have been enticed into using a single common for the layout. That is what had me pose the question.

As I said above, I plan use 180 W PoHo on two TPCs and a PW ZW 275 on the other two - A handle on one and D handle on the other for the conventional feel.  All three powering devices will go into 20 Amp outlets. There will be no more than 3-4 feet between where the transformers are and the outlet receptacle is on the wall. I have no plan to diddle with the plugs or cut the wires on the transformers. That I consider above my skill level. 

The wire from the PoHo with its Molex?? connector will be as it came from the factory. The wire from the ZW will be approximately 2-4 feet distant to get the quick connects on the TPC and on the ZW posts. I have no plan to diddle with the PoHo connector to make it shorter. Again, above my skill level.

The common will come from the four TPCs and go to a bus bar using 14 AWG wire. A fifth,sixth and seventh hole in the bus bar will have 12 AWG Romex. This romex will act as an around the layout common. I have it planned to connect to intermediate drops every 8-10 feet, taking the common from that up to the tracks on the table. 

The power wires from the TPCs, again 14 AWG go to BPCs which connect to the power bus around the layout, thru terminal strips, again approximately every 8-10 feet to the tracks above. The feeders are 14 AWG from the terminal strips to the tracks. 

The layout is a large U with one tail of the U extended. Basically the U is 28' long and 20' wide. There is a 2.5 walk thru down the middle which I have omitted from the width size. There are multiple levels - three on the basic U - and the common/power drops go to these levels as well, so feeders may be off a bit from the 8' on the mid and top levels. 

One tail of the U has an additional 10' long and 8' wide, used as an Intermodal Yard.  There are two under table storage yards each about 18' long and 8' wide. These under storage and intermodal yards will be powered with a separate powered system/common wiring. 

No accessory or turnout or lighting will run on this power. That will all be separately powered/commoned off of different transformers. 

Before I started the rewiring, The conventional and my two TMCC engines ran fine with two TPCs and two PW ZWs using 14 AWG wire for connection to the power units and for the bus around the layout. Perhaps I was lucky or didn't notice the heat buildup, certainly there was no noticeable melting on any wire that I can see. I recognize that there will always be different views.

Am I close to OK with the 12 AWG common and 14 AWG Power or am I really asking for trouble now that I have added power, and conceivably adding more power later if needed. 

Ralph

I think you are good to go on wiring capacity! Pretty good power center arrangement and load distribution in my judgement.

FYI, when talking wiring sizes, we were talking about the low voltage side of the transformers.  As far as the 110V wiring, #16 wire from any of these devices is more than sufficient!  Remember, the high voltage side will have about 20% of the current of the low voltage side, and they have more voltage to throw away on a small voltage drop.

Here is some food for thought:

Putting all your power devices in one centralized location is absolutely the WORST solution with respect to power wiring!  If you have 4 devices feeding one end of your bus, everything adds together.  If, on the other hand, you put half of the devices at one end (the TPCs) and half on the other end (PW ZW),  the currents flowing from the opposite ends will partially cancel each other, minimizing the voltage drop and heating in the Common bus.

If your Common bus is a loop, placing the devices diametrically opposed across the loop will accomplish the same thing.

It is a lot easier to distribute the DAT/COM signal on small-gauge wire than it is to bus 20+ amps around.

Thanks Guys.

Appreciate the direction Dale. Moving it now is easier than moving it after the meltdown.

Ralph