Bus Wire Question

[msacco]

I'd like to know if a bus wire has to be a loop of wire that starts with one connection to the transformer and has another end that loops around and connects to the transformer a second time.
Or can it be just a long run of wire that has only one connection to the transformer and terminates somewhere underneath the layout further down.
I ask this because in Pete Riddle's book he shows a bus looping all around with two connections at the transformer. It seems like more wire this way.
Apologize for being cluesless, but just wondering if there's a difference.

thanks,
Mike S.

[Anonymous]

I have done it both ways over the years Mike and never could discern any improvement or difference in voltage drop, component heat, engine performance or car lighting on the far reaches of my benchwork layout [23 x 13] or on my high, 5 track, twin shelf RR in our mountain cottage[14 x 28].

Curently my benchwork layout 's Bus is four #12 gauge Hot color-coded wires to four separate power districts[3 tracks and yard] with a #10 White code Common return conductor to the transformer [which does not also loop back ]. The single #10 is a return and all an additional return conductor ("loop"} would accomplish is to double the return circuit capacity . I used to think it improved electrical efficiency in low voltage systems---which I now doubt as regards an O-gauge layout. Of course, a Common loop cannot hurt the system!

(Simplistically, current flows from the transformer via the Hot conductor to center rail, then thru pickup rollers, thru the motor/lights and then via the engine's frame, wheels/axles to the outside rail(s) and thru the Common return conductor back to the transformer. Realistically a plain simple electrical circuit is completed in this process).

[Anonymous]

You can do it either way but the advantage of a loop is that it has less voltage drop because the current has 2 paths and it evens things out. Depends on the size of the layout to determine if it is worth looping. My layout is L shaped maybe 39 by 20 by 10 and I loop all the busses for the track. For accessories it is less important. For my ground bus loop I use 3 ,12 gauge house wires and loop it around the perimiter,I also cross connect so it has vitually no voltage drop. If voltage drop is a concern for long runs and you dont want to use a loop then use a sufficently gauged wire probably #12 and there will not be a voltage drop issue. If you give the size and load on the wires I could be more specific.

Dale Hz

[msacco]

Thanks guys. It sounds like for my double 4x8 layout I can go with a single run for my buses.

Mike S.

[lionelsoni]

This loop is what the British call a "ring main". They allow it to be made of what amounts to AWG13 wire fused at 30 amperes, whereas the same wire must be fused at 20 amperes if not in a ring. The idea is that, since it is supplied from each end, the wire is able to carry twice the current. However, it is easy to show that, if a load draws its current, for example, from a point 10 percent from one end, 90 percent of the current will flow from that end. So, if someone switches on a heavy load near the fusebox, nearly 30 amperes could be flowing in a wire that is rated to carry only 20. (We would allow only about 17 amperes if that wire size were used in the US.) This is one reason why ring mains are not allowed here.

However, for toy trains, a ring main is pretty harmless if you size the wire for the full current; that is, don't assume that it can carry more current because it is connected at both ends. In any case, you will reduce the voltage drop by half.

[Anonymous]

Mike
IF and when you check for voltage drop at your layout's most distant place, do so with a substantial load such as a lighted passenger train passing thru the area at regular speed. With no-load you cannot get an accurate IR Drop reading.
We used to wire Common return loops with cross layout grids on our Conventional layouts on the theory that it would reduce voltage drop and improve efficiency---but you cannot reduce it if you have no measurable drop to start with. You can certainly experience it with undersized conductors, long wire runs and /or poor connections. Under that circumstance one should take steps to correct the problem.