![]() As can be seen in the calculations to the left, 14 AWG wire allows for at least 10.1 V for the last device which will work for our application.Ģ2/10 (22AWG 10C) Stranded CM Security CableĬoded panels were the earliest type of central fire alarm control, and were made during the 1800s to the 1970s. Using 14 AWG wire however, provides much better results. Applying the same calculation with the 16 AWG wire yields 5.5 V for the last detector which is still below the minimum required voltage of 8.5 V so this wire gauge also has too much resistance because of its small size. This means that the last device will have -1.8 V to operate with which obviously will not work. Connecting the system with 18 gauge wire will cause the following voltage drop: 29 devices (All but the last one) x 35 mA (current per device) x 3,000 feet (assume all the wire is in front of the last detector) x 6.5 ohms (resistance per 1,000 feet of wire) = 19.8 V. These units have a minimum voltage of 8.5 VDC, a maximum of 30 VDC and a nominal voltage of 12 VDC. Let's say we have 30 smoke detectors, each requiring 35 mA of current. For this example, we are going to combine all but the last device into one to make sure that the last unit in the chain receives enough voltage to operate. Just like the wire, each detector is going to exhibit its own voltage drop. Let's consider a system where the devices are connected in series. ![]()
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