Low Volt Wiring – Unit 1

Low Volt Wiring – Unit 1


This course is designed to educate technicians in low volt aspects of access control and security systems. The subjects and terminology of this course is meant to cover many of the basic and advanced wiring scenarios we as technicians face daily.

Our installations are custom. Rarely does a “kit” cover the all the devices required for an access or security installation. Relays, timers, switches, motion sensors and other input devices are mandatory elements of a secure system. Sirens, electric strikes and mag locks are examples of devices that are controlled by a system’s output.

Example: A card reader is an input device. Upon a valid card read, the system will energize the required relay or output to control the locking hardware.

Before we wire up our system, let’s look at the terminology and concepts we need to be aware of to make it work now and far into the future.

Alternating Current A/C is the power source we use to turn on our alarm panels, access control systems and power supplies. The power supplies often use 120 volts hard wired or by way of a plug-in cord. Alarm systems and many access control systems use a 16VAC plug-in transformer to power up the equipment. These systems may also have a 12VDC output available to power a limited number of devices.

Regarding access control and security power, two of the most important considerations are voltage and amperage. Our industry uses 12 volts DC and 24 volts DC to power our sirens, mag locks, strobes, electric strikes, relays and timers. Each of these devices has a power requirement of 12 VDC, 24 VDC or a range that includes both voltages. If the voltage requirement of each device matches the voltage of the power supply, the system should operate.

To make sure it does operate, the other factor we need to consider is Amperage (or Current). Amperage or Amps is the amount of power behind the voltage. (Add too many devices to your system and it won’t work regardless of the voltage). The voltage is a rating. 12 or 24 VDC. It is chosen based upon the size of the building and the power required by the devices connected to the system. Devices can be backed up by a 12VDC battery. If 24 VDC battery back-up is required, two 12VDC batteries will need to be wired together “in series”.

In Series means the devices you terminate are added together like the batteries in a flashlight. One AA, AAA, C or D battery is 1.5 volts DC. The batteries are inserted so the positive and negative terminals touch. They are inserted in-series. With 3 batteries, you get 4.5 VDC. With 4 batteries, 6 volts DC is the total power.

In Parallel, connections are made by terminating all the positive points together and all the negative points together. If we are using 12-volt batteries, we end up with 12 volts DC as the total output voltage. We didn’t increase the voltage; we made our existing voltage last twice as long.


The terms In-Series and In-Parallel don’t just apply to battery power. Burglar Alarm system devices like window contacts, are sometimes wired in-series. This is also known as a Normally Closed Loop. All devices should have their own unique wire home run (no splices) back to the control panel. Wiring more than 1 device on a wire may make troubleshooting more difficult. Which device caused the fault?

Fire alarm system devices are wired Normally Open. Their wiring is run in-parallel. A resistor is placed in at the end of the line, inside the last input device, to monitor the circuit. Wiring configurations such as addressable loops, wireless and other new technologies require knowledge of the products we’re installing before the 1st wire is run.