Electronics - Wire Sizes and Voltage Drop
Voltage drops are an issue railway modellers have to contend with. Generally, a few simple rules of thumb are enough to cope with most situations.
Every piece of wire is a resistor - it will drop some voltage and convert that power into heat. For model railways, it is really only the reduction in voltage that matters - even on a very large layout there shouldn't be enough heat to worry about. A minor voltage drop of up to 1V or so is usually acceptable.
You only really start to get problems when two or three of the following happen together:
The longer the wire, the greater the voltage drop.
The higher the current running through the wire, the greater the voltage drop.
The thinner the wire, the greater the voltage drop.
Wire Lengths
For model railways, a short distance can be considered to be 2-3 meters as the crow flies. The actual wire length could be more like three times this: one wire each way, plus an allowance for bends, plugs, etc. This typically works out to the same or adjacent baseboard, or the same station.
A medium distance would be 5-10 meters, to the far side of a typical model railway room.
Unfortunately, a large distance is something most of us don't really have to worry about.
Wire Sizes
For simplicity, we can group wires into three thicknesses:
Thin wire would be the sort found in grey IDC ribbon cables (multi strand), or wire wrap wire (single strand) often used when building model signals or doing train lighting. These are rated at up to half an amp or so, and have AWG numbers around 27-28.
Normal wire is the sort commonly used by modellers. Single strand telephone wire or multi strand wire from rainbow ribbon cable, light duty or hookup wire from electronics shops, or most wire sold in model shops. These are all rated at about 1-1.5 amps, with AWG numbers of 24-25.
Heavy wire is anything thicker than the above, with current ratings of 3 amps or more and AWG numbers of 22 or less, right up to the heavy copper braid sometimes used for common return wiring.
You can always make a thicker wire of the next size by doubling or tripling up on the smaller size. This can often be a simpler and easier choice than using thicker wire.
Currents and Loads
A light load would be less than 0.5 amps. This would be one, two or a few signals (not memory wire types), electronic sensors, relays, lights, etc. Any size of wire can handle this over pretty much any distance.
A medium load would be 0.5 - 1.5 amps. This would be traction current for one or two locos under DC or individual track feeds under DCC, or station-sized groups of the lighter loads, or low-power point motors such as Tortoise, Peco low-power or most continental types. Normal wire should be adequate for these over short distances, but you will probably need to go to heavier wire over medium distances. Point motors do push this limit, so for crossovers or diode matrix applications, either run separate wires to each point motor or use heavier wire.
A heavy load would be 2 amps or more. This would be high power point motors, Kaydee uncouplers, point motor or traction common return, DCC buses, main power feeds to entire stations or the whole layout, etc. These really need heavy wire or double/triple up on standard wires.
Connectors and Switches
Plugs and sockets also have maximum current ratings, and each pair will impose a slight additional voltage drop. The common D-type connectors and similar small plugs are rated at 1 amp, so are compatible with normal thickness wire. If you double up this type of wire, then consider doubling up on connector pins as well. If you need to use heavier wire, then allocate two pins (three for extreme cases).
Switches also have maximum current ratings, and the common types of small toggle switches and push buttons are often rated for only 1A or so under DC. This matches up with normal thickness wire, but there can be problems when handling heavier loads. You can wire multiple poles in parallel to handle higher loads.
The commonest switch problems tend to be with push buttons for point motors - these are generally overloaded, especially when released to break the circuit, and do fail from time to time. This yet another reason to use a CDU for point motors: it is easier on the switch (the release current is quite low), and a stuck switch should not cause a high-power short circuit and burn out a point motor.
Summary
Everything depends on the size of the layout: scale, physical size, number of trains in motion, lighting, total power requirements, etc. A small single-board layout can get away using normal wire for everything, and N gauge layouts can even use the light-load grey ribbon cable for traction over short distances.
Every piece of wire is a resistor - it will drop some voltage and convert that power into heat. For model railways, it is really only the reduction in voltage that matters - even on a very large layout there shouldn't be enough heat to worry about. A minor voltage drop of up to 1V or so is usually acceptable.
You only really start to get problems when two or three of the following happen together:
The longer the wire, the greater the voltage drop.
The higher the current running through the wire, the greater the voltage drop.
The thinner the wire, the greater the voltage drop.
Wire Lengths
For model railways, a short distance can be considered to be 2-3 meters as the crow flies. The actual wire length could be more like three times this: one wire each way, plus an allowance for bends, plugs, etc. This typically works out to the same or adjacent baseboard, or the same station.
A medium distance would be 5-10 meters, to the far side of a typical model railway room.
Unfortunately, a large distance is something most of us don't really have to worry about.
Wire Sizes
For simplicity, we can group wires into three thicknesses:
Thin wire would be the sort found in grey IDC ribbon cables (multi strand), or wire wrap wire (single strand) often used when building model signals or doing train lighting. These are rated at up to half an amp or so, and have AWG numbers around 27-28.
Normal wire is the sort commonly used by modellers. Single strand telephone wire or multi strand wire from rainbow ribbon cable, light duty or hookup wire from electronics shops, or most wire sold in model shops. These are all rated at about 1-1.5 amps, with AWG numbers of 24-25.
Heavy wire is anything thicker than the above, with current ratings of 3 amps or more and AWG numbers of 22 or less, right up to the heavy copper braid sometimes used for common return wiring.
You can always make a thicker wire of the next size by doubling or tripling up on the smaller size. This can often be a simpler and easier choice than using thicker wire.
Currents and Loads
A light load would be less than 0.5 amps. This would be one, two or a few signals (not memory wire types), electronic sensors, relays, lights, etc. Any size of wire can handle this over pretty much any distance.
A medium load would be 0.5 - 1.5 amps. This would be traction current for one or two locos under DC or individual track feeds under DCC, or station-sized groups of the lighter loads, or low-power point motors such as Tortoise, Peco low-power or most continental types. Normal wire should be adequate for these over short distances, but you will probably need to go to heavier wire over medium distances. Point motors do push this limit, so for crossovers or diode matrix applications, either run separate wires to each point motor or use heavier wire.
A heavy load would be 2 amps or more. This would be high power point motors, Kaydee uncouplers, point motor or traction common return, DCC buses, main power feeds to entire stations or the whole layout, etc. These really need heavy wire or double/triple up on standard wires.
Connectors and Switches
Plugs and sockets also have maximum current ratings, and each pair will impose a slight additional voltage drop. The common D-type connectors and similar small plugs are rated at 1 amp, so are compatible with normal thickness wire. If you double up this type of wire, then consider doubling up on connector pins as well. If you need to use heavier wire, then allocate two pins (three for extreme cases).
Switches also have maximum current ratings, and the common types of small toggle switches and push buttons are often rated for only 1A or so under DC. This matches up with normal thickness wire, but there can be problems when handling heavier loads. You can wire multiple poles in parallel to handle higher loads.
The commonest switch problems tend to be with push buttons for point motors - these are generally overloaded, especially when released to break the circuit, and do fail from time to time. This yet another reason to use a CDU for point motors: it is easier on the switch (the release current is quite low), and a stuck switch should not cause a high-power short circuit and burn out a point motor.
Summary
Everything depends on the size of the layout: scale, physical size, number of trains in motion, lighting, total power requirements, etc. A small single-board layout can get away using normal wire for everything, and N gauge layouts can even use the light-load grey ribbon cable for traction over short distances.