What size and length for dropper wires

[Vistisen]

I am building a layout with about 85m of track where I expect to be running 4 or 5 trains at the same time. I have installed a 5 amp track power bus which uses a twisted pair of 2.5mm 13AWG DCC Concepts cable, But I am wondering about what gauge and length dropper wires should be. I have a lot og AWG16. I can see that it is rated to 3.6 amps. Is that OK for use as dropper wires. And how long can a dropper wire be before voltage drop becomes a problem?

[John ks]

Short answer is, droppers are as large & as short as practical.

 

If I can believe the internet than AWG16 is about 1.3mm & that should be more than adequate & droppers up to a metre long should be fine

 

Longer answer

The resistance of a conductor is determined by its cross-sectional area, type of material & length

 

The voltage drop along a conductor is determined by the current flowing through it, its resistance & its length.

 

For lowest voltage drop you need the largest & shortest conductor practical.

 

I did the following experiment & with 0.5amps I got 0.056volt drop along 1metre of wire. (Which is about 1.0mm or possibly 0.75mm?)

If you want to try it yourself, use a 12v 10 to 20Watt bulb.(this will be a similar load of up to 4 locos)

 

 

 

Other things to consider

There multiple parallel paths from the bus wiring to the rails through the droppers

It is only when the loco is directly above a dropper that most of its current (90 %+) will be going through one dropper, the rest will go through adjacent droppers

 

You say you have 85M of track, how this is laid out will determine the size & layout of the bus wiring

Worst case is you have all 85M as a single track end to end & the booster is at one end. In this case your bus wiring may have to go to 10mm or larger

 

Better case is 2 main lines of about 25M & the other 35M of track is in passing loops & sidings

 

More things to consider

With this much track you should divide the layout up into power districts.

At least one for each main line & one for each yard.

 

Something like this?

 

 

I have only shown one of each bus wire to make it easier to follow

 

All buses return to a terminal block to make fault finding easier.

Each bus could have a circuit breaker at the terminal strip

To find a fault you disconnect 1 power district at a time from the terminal strip until the fault goes away

The fault is in this power district, reconnect the other power districts

If the fault returns then there is 2 or more faults. Repeat disconnecting power districts until you find all faults.

 

Hope this helps

 

John