Wiring Question

[cheech]

I have a siding to wire. Lionel tubular, with a lockon. For a lot of reasons, I plan to run the wire on the tabletop. To keep the wire with low visibility, I plan to use 22 gauge. The siding will have a toggle to power up, it will have an engine that will start up from time to time and may be a lighted passenger car or two stored. Would this be too small a gauge. Is there a formula for wire related to transformer wattage?

ralph

[J. Daddy]

Well to keep it simple... How big is the layout?, how far is the siding feeders from your your main layout feeders? I use nothing smaller than 16 guage wire for running power under the track the total length of the layout. Than I use 18 or 20 guage wires for feeders to the track or track clip. This will reduce the resistance experienced in sectional track or 3 ft sections of your layout. What transformer are you using? 

[Texas Pete]

cheech

I have a siding to wire. Lionel tubular, with a lockon. For a lot of reasons, I plan to run the wire on the tabletop. To keep the wire with low visibility, I plan to use 22 gauge. The siding will have a toggle to power up, it will have an engine that will start up from time to time and may be a lighted passenger car or two stored. Would this be too small a gauge. Is there a formula for wire related to transformer wattage?

ralph

 

  The relevant information in this case would be the current (amperes) drawn by the loco and the lighted car, and the length of the wire run.  There is a formula, but I'm a "seat of the pants" kinda guy and I don't know it.  Hopefully Bob (lionelsoni), who is very knowledgeable about electronics, will be able to help out with some numbers.  Meantime, the seat of my pants tells me that unless the wire run is very short I wouldn't go any smaller in wire gauge than 18 (if it were my setup).

Texas Pete

 

[lionelsoni]

There are two considerations:

The wire should be heavy enough to survive until the transformer's circuit breaker, or whatever overcurrent protection you have, opens the circuit.  This ranges from about 5 amperes for the likes of a 1033 through 10 amperes for a KW to 15 amperes for a ZW or Z.  You should use no smaller than 20 AWG for 5 amperes, 16 AWG for 10 amperes, and 14 AWG for 15 amperes.  If the size of your transformer is a problem, you can always insert an external circuit breaker or fuse into the circuit.

The wire should be heavy enough so that the voltage drop between the transformer and the train is not too great, that is, well under 1 volt.  Assuming that a typical train draws about 5 amperes, apply Ohm's law, that the voltage drop is the product of the (5-ampere) current and the wire resistance.  The resistance of 22 AWG (which is too small for safety anyway) is about .016 ohms per foot, resulting in a 1.6-volt drop over 20 feet.

AWG  Resistivity, ohms/foot
10   .001
12   .0016
14   .0025
16   .004
18   .0063
20   .01
22   .016

[thankey]

 

AWG gauge	Conductor Diamet Inches	Ohms per ft.	Maximum amps for chassis wiring	Maximum amps for power transmission
10	0.1019	0.0010	55	15
11	0.0907	0.0013	47	12
12	0.0808	0.0016	41	9.3
13	0.072	0.0020	35	7.4
14	0.0641	0.0025	32	5.9
15	0.0571	0.0032	28	4.7
16	0.0508	0.0040	22	3.7
17	0.0453	0.0051	19	2.9
18	0.0403	0.0064	16	2.3
19	0.0359	0.0081	14	1.8
20	0.032	0.0102	11	1.5
21	0.0285	0.0128	9	1.2
22	0.0254	0.0161	7	0.92
23	0.0226	0.0204	4.7	0.729
24	0.0201	0.0257	3.5	0.577

Obviously, if you run more pairs of 22ga feeders, you can increase its effective capacity.

[lionelsoni]

The ampacities that I use are those of NEC 240.4(D) down through 18 AWG and extrapolated from them for smaller wires:

AWG  Ampacity
10   30
12   20
14   15
16   10
18    7
20    5
22    3.5
24    2.5

[cheech]

Thanks for the information and charts. 

Some more info I omitted from my original post. The power source is a Pw ZW. The power bus around the layout is 12AWG. I use terminal strips.  The wire I planned to the siding  will go from a termial strip to the track, approximately 3 ft. distance. The power circuits have 10Amp fuses. I use a TVS for each track connection.

I'll probably rethink the wiring to the siding. Actually, getting power to this 'afterthought' has turned into a bigger job than I contemplated. Since I use the 22AWG to power the switches/lights, I thought it would work for the siding as well.

Thanks again.

Ralph

[lionelsoni]

Since the distance is only 3 feet, voltage drop is not a problem even with 22 AWG.  You say you won't be powering much on that siding.  So how about just connecting the number-22 wire to the terminal strip through a 3-ampere fuse?  That will protect the wire and let you get enough power to the siding to do what you want.