Wire Selection
In practice, 18-gauge stranded should be the minimum size wire used for any system wiring. In applications with long runs of wire, or when operating units that have high current requirements, use the chart below as a guide for selecting the proper wire size. Stranded wire, versus solid wire, is recommended for electrified hardware applications. Stranded wire offers greater resistance from the vibration and flexing within door and frame systems. For more information concerning wiring of low-voltage circuits refer to the National Electrical Code (NFPA 70).

Current At 24VDC

NOTE : All wire runs are measured one way, but electricity flows to and from the electrified device. Therefore, the wire run is double the length that you are looking at. For example, a 100-foot run of 18 gauge 2 conductors is realistically, 200 feet of wire. As one wire is the hot going to the device and the other is the neutral coming back to the panel.

The wire size is different for the two voltages. The reason for this is that at a higher voltage the current draw is less than that at lower voltages. This must be kept in mind when looking at wire runs and voltage for your system.

Types Of Wire
Now that you’ve learned about wire sizes, we need to look at what type of wire you will need for your job. If the project requires you to install wire in a door frame or wall, a plain-jacketed wire will do. If the job requires you to run wire through the wall or ceiling, which are also being used for the A/C and Heating return air system for the building, you will need to run a plenum rated wire.

The "jacket" on a jacketed wire helps to protect the wire from being cut or broken due to movement of a wall or ceiling. The "shield" on a shielded wire will stop or limit electrical noise from other devices near the wire. Transformers, ballast or high voltage wires may interfere with the transmission of data from a controller and reader or keypad.

An 18 AWG 2 conductor jacketed wire should be used when powering locks and remote readers. Zip cord or speaker wire do not have a jacket and should not be used. A 22 AWG 6 conductor jacketed shielded should be used when installing card readers and/or keypads.

Jacketed wire comes in many colors but white, gray and red are the most common. White is easy to write on and visibly stands out better. Gray is used when your running wire along side a phone line and you want it to blend in. Red is mainly used with fire alarm systems, as the color would indicate.

The cost difference between "Plain" wire and "Plenum" wire is minimal. Because of some laws and NFPA code requirements and to help eliminate guesswork on your part, you may want to install the plenum wire in all your jobs. In this instance, plenum wire is accepted for all conditions.