Wiring Street Lights on a Fairly Large Layout

[BradKT]

I read some very interesting comments from a 2008 thread on this site about how copper adhesive tape was being used to secure to the underside of a plywood layout and then street and building lights were connected to it.  If anyone has any experience doing this, I would like to hear from you.

My layout is L-shaped.  One side is 9'x5' and the other side is 9'x6'.  This makes one side of the L-shape 14' long and the other side 9' long.  There is an access hatch where they intersect.

One of my major questions is how do you connect the wires from the street lights to the tape?  Would you use metal screws?  Somehow, I don't think that soldering would be a practical, effective or secure way to do this. I am assuming that you make two runs of tape (for the positive and negative) and connect corresponding wires from the lights to the tape.  Assume that the on/off control would be one or more Atlas switches, so the wires from the buildings and lights would have to run to the tape from the switch and the switch is connected to the transformer.  I use a separate transformer for the lights and switches, as well as the railroad crossing signals (which I also intend to wire this way).

Any thoughts on this subject would be appreciated.  If this can work, it would certainly solve a problem for me re: wiring up the street and building lights on my layout.  I have about 75 total lights on my layout that need to be wired.

[Jim Banner]

Soldering wires to copper tape works fine, as long as there is no tension on the wires.  In practice, this can be achieved by installing a small screw eye next to the tape and tying the wire to it, or better, attaching the wire with small cable ties.

But 75 assorted lights on one run of tape is a different matter.  Like wire, tape has a maximum allowable current.  And like wire, the currents to the lights cause voltage drop and the voltage drop causes dimming of the lights farthest from the power source.

If you feel you have to use tape, at least put your power source near the electrical center of the layout with tape runs going in both directions away from it.  This will halve the current going through any particular piece of tape.

If you do not like soldering, then use screws, but do not put them through the tape.  To do so would reduce the current carrying capacity of the tape.  Rather, put the screws beside the tape and use two brass, copper or stainless steel washers on each screw.  One washer should bear against the tape and the other washer should hold the wire against the first washer.  This avoids cutting the wire with the screw head and keeps from damaging the rather fragile tape by pressing the wire through it.  The screws should be round head, not flat head.

Personally, I would prefer to connect up the lighting a different way.  I would install one heavy bare wire, either #14 or even #12 gauge, down the centre of each side of the 'L'.  I would cable tie this wire to screw eyes every foot along its length.  This wire would form the return for all my lights and could be connected to one side of my power source (using insulated wire of the same size) at any place along its length.  Then I would install one or more bare supply wires parallel to the return wire but set away from it and from other supply wires by about 3 inches.  These supply wires would also be cable tied to their own sets of screw eyes on 12 inch centres.  With your setup, I would probably run one supply wire down each of the two sides of the 'L' for two sets of building lights and another supply wire down each of the two sides of the 'L' for two sets of street lights.  This would break your lighting into 4 circuits of about 20 lights each to simplify trouble shooting and to limit the power in any one circuit.  It would also leave you some room for expansion on each circuit in the future. 

I would connect the supply wires to the power source as follows:
(1) a single fuse between the supply terminal and a block of four fuses.  This single fuse would be the main fuse, and should be rated no higher than the rated output of the power supply.
(2) four sub fuses, each connected from the main fuse to a toggle switch.  These branch fuses would protect the railroad wiring and should be rated at no higher than 5 amps.
(3) four toggle switches, each connected from one of the branch fuses to one of the supply wires.

Even though the supply wires under the table would be bare, the wiring used in (1), (2) and (3) above would be insulated.  These wires and the bare supply wires under the table should be about #16 gauge with one exception - the wire from the supply to the main fuse should be #14.

What you would have at this point is a total of 5 bus wires making up 4 circuits, each circuits protected by its own fuse.  At any one point under the layout, you would have 3 bus wires, one for the street lights, one for the building lights, and one return.  Being bare, you can connect the pairs of wires coming from buildings and street lights anywhere along the bus wires, one wire to the return bus wire, the other to the appropriate supply wire.  Soldering the joints horizontally is a lot easier than soldering upwards, and the joints do not have to be taped.  I would still cable tie the building and street light feeder wires to screw eyes within 6" of where I attach them to the bus wires, but those screw eyes are already in place on one foot centres holding the bus wires.  The only places where you might have problems would be going around switch machines (easy if you use a few extra screw eyes) or under or over other metallic barriers such as choke cables (easy solution is to slip insulation over the wire at this point.)

As far as your power source is concerned, you could be looking at something around 100 watts (volt/amperes) at 12 volts.  This is a fairly large, relatively expensive transformer or a virtually free computer power supply.  Many computer power supplies are rated 8 amps or more on their +12 volt output and used computers can often be had for the asking.

Jim

[BradKT]

Thank you Jim.  You have given me something to chew on.  I was definitely going to break the runs down into either 4 or 6 different sections.  One thought that I had was to use a 3/8" to 1/2" thick plywood square or rectangle (maybe 12"-18" wide) to mount everything for one section on (tape or wires and connection points thereto) which I could then secure with screws under the layout to the benchwork ribs and then just run all of the connecting wires to it (to the power source and the lights)...and do this for each section of lights.  Your ideas on using the eyelets makes a lot of sense, as does your suggestion on how to connect to the tape without breaking it.

I have to think about the bare wire route.  I am definitely going to sketch this one out and have it clear in my head before I do it.  I am just gathering information now and am not going to get to this until probably May. 

I have several DC transformers (Atlas, I think) which all have an input  connection for DC accessories.  Do you think that this would be a sufficient source for my power supply (even if I have to use more than one?).  If so, would I still have to install fuses?  I am not at all well versed in electrical jargon.  I am going a check out the Model Railroading booklet on wiring before I attempt this.

[Jim Banner]

Your dc power packs will have some sort of rating on them.  They might, for example, be rated at 12 volts 16 VA (or 16 volt.amps)

Then you need to know how much your lights draw.  Small grain-of-wheat bulbs might be rated at .065 amps at 12 volts.  This would be 12 x .065 = .78 watts or .78 VA.  So you could operate 16 / .78 = 20 of them off one power pack rated 16 VA.  Note that Watts and volt amps or VA are about the same thing.  Eighty such bulbs would require 4 power packs rated at 16 VA.

The bulbs in your buildings could be larger and might draw, for example, .15 amps each at 12 volts.  These bulbs would each draw .15 x 12 = 1.8 VA.  Then a 16 VA power pack could light only 16 / 1.8 = 8 of them.

Checking out other sources of wiring information is a good idea.  You will find that there are a number of good ways of doing things (and even more bad ways.)

Jim

All UL approved power packs have a built in circuit breaker to protect them against over load.  So you are not required to use a fuse.  However, small power packs often burn out their transformers, even though they are protected by circuit breakers.  So you might want to use a fuse anyway.  In the above example, a 16 VA power pack rated at 12 volts can put out 16 / 12 = 1.33 amps.  A 1.25 amp fuse would be a good size to use.  An old Lionel transformer might be rated at 50 watts at 14 volts output.  Its maximum output current would be 50 / 14 = 3.57 amps.  You could use a 3.5 amp fuse with this one.