# Wiring

## AWG Wire sizes

Wire diameter is specified in AWG number (American Wire Guage) which is a stupid and overly complex system. Of course. "By definition, No. 36 AWG is 0.005 inches in diameter, and No. 0000 is 0.46 inches in diameter. The ratio of these diameters is 1:92, and there are 40 gauge sizes from No. 36 to No. 0000, or 39 steps. Because each successive gauge number increases cross sectional area by a constant multiple, diameters vary geometrically. "^ So the diameter of wire of AWG guage n is 0.005 * 92 ^ ((36 - n) / 39) inches or 0.127 * 92 ^ ((36 - n) / 39) mm. Except... for AWG sizes larger than 0 which are

•     00 = 0.3648" or 9.266mm
•   000 = 0.4096" or 10.405mm
• 0000 = 0.4600" or 11.684mm
inches mm

## 4 pin peripheral power cable

The four pin peripheral power cable dates back to the original PC. It was used for floppy drives and hard disks. It's still around and is now also used for all kinds of things including add-on fans, extra video card power, supplemental motherboard power, and case lighting. It's as old as the hills but is still very widely used. The connector is shaped so that it only fits in one way. You don't have to worry about inserting it the wrong way. People often use the term "4 pin Molex power cable" or "4 pin Molex" to refer to a four pin peripheral power cable. It's not a technically useful term because the 4 pin 12 volt cable is also a 4 pin Molex cable (Molex makes lots of connectors) but "4 pin Molex" is commonly used to refer to peripheral cables anyway.

Pinout
Pin number Wire color Description
1 yellow +12 volts
2 black ground
3 black ground
4 red +5 volts
Connector part numbers
Socket housing Socket Pin housing Pin Maximum current per circuit
AMP 1-480424-0 AMP 60619-1 AMP 1-480426-0 AMP 60620-1 13 amps

I don't know of any official definition of the maximum current allowed in a peripheral cable. The connector can handle 13 amps according to the manufacturer. But you normally find 18 awg wire in the peripheral cables. If you have an 18 inch cable (about a half a meter) and are running 13 amps through 18 gauge wire then you get a voltage drop of about 0.25 volts counting both the power wire and the ground (it's got to go both ways) and the dissipation is about 3.3 watts. That's not good. I've just played it safe and listed the maximum current as 5 amps.

Unofficial cable/connector maximum wattage delivery
Voltage rail Number of lines Maximum current Maximum wattage
+5 volts 1 5 amps 25 watts
+12 volts 1 5 amps 60 watts

You will occasionally run into peripheral connectors which don't have all four wires. They are usually 12 volt only cables intended for fans. Never plug one of those into a disk drive. Drives expect both 5 and 12 volts to be provided. Some of the two-wire peripheral connectors are for speed-controlled fans. That means that the voltage changes depending on the desired fan speed. The connector will only provide 12 volts when the fan is going full speed and the voltage decreases to slow the fan down. Definitely don't plug that one into anything but a fan! Normally this kind of peripheral connector has "fan" printed on it to warn you. As long as a peripheral connector has four wires: one yellow, two black, and one red and it doesn't have some kind of printed warning attached then it's a standard peripheral cable and you can plug it into anything.

## 3 and 4 way switch wiring:

With reguard to wireing in the home:

Thermostat circuits are generally Class 2 power limited circuits as defined in NEC article 725. They must be wired with UL listed cable labeled "CL2". Category 5 network cable is usually listed as type "CM" (article 800) but some styles may be dual labeled as "CL2" also. If you're careful to buy the right cable, article 725 (remote control) circuits can be run in the same cable with article 800 (communication) circuits. There are fixed legal limits on the power (not just voltage) that these circuits can supply (think fuses). Read and understand the NEC before doing any wiring in your house. This kind of wiring can burn down houses if done wrong.

Questions:

Cables +

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