Originally Posted by Ffffreddd:
As I was reading discussions from others regarding the use of various size wires it occurred to me that voltage drop probably would not affect a TMCC engine all that much. Within reason of course. I doubt the engine really uses the full 18 V. For some reason I thought it regulated it to a steady 12vdc and then distributed accordingly. At least for DC cans anyways. No idea about the AC motors.
Aside from that, even though NEC allows for certain exceptions to use parallel wires to reduce voltage drop and not increase current carrying capacity, very the equivalent wire size is always less than the source. Most residential wiring that is your parallel 120vac feeds coming to your house panel.
I have yet to see a tap on a transformer or a wire coming off a 180 watt brick that have a measured greater than 14 gage wire. I know some people swear by running much larger wires but at some point doesn't the wire become a load in itself?
The TMCC signal is not affected by the voltage drop.
There is 14awg for the output supply from the 180 watt powerhouse.
Then there are two scenarios
- The 180 watt powerhouse is connected directly to the track or buss. In this case, you are correct- it doesn't make sense to use heavier wire downstream.
- The powerhouse is connected to a ZW-C, TPC or TIU. Here the 14awg is only a short run to a controller. ( or direct from a ZW or ZW-L) Using heavier wire makes sense from the controller to the track to reduce the voltage drop.
- Conventional operation is more sensitive to voltage drop as lower voltages are needed and any drop can be significant.
- The resistance ratings for 1000' are very low, so at shorter distances, the wire doesn't become a load.
I found this voltage drop calculator that allows all of the inputs. A 25'-50' buss is not unreasonable for a small to medium layout. 14awg works ok, to about 30', unless you want to have the full 10amps at the end for 18vac.
Change it to 5vac for 6 or 10 amps at the end, and you need some heavy stuff.
I can see why the Dealer Display Layouts from the 50's used a solid bar buss.
On a follow-up note, the chart came from here: American Wire gauge and current limits and is for a single conductor ,whereas, the NEC table is for a 3 conductor. These are for ampacity and not voltage drop.