Safety and Security Technology Fundamentals
What this domain covers
The Safety and Security Technology Fundamentals domain tests the electrical, signaling, and network basics that every other domain builds on. Expect questions on Ohm's law and power, series and parallel circuits, voltage drop, power-limited circuit classes, alarm circuit supervision, and the IP networking used by modern recorders and controllers.
Core rules
- Ohm's law: V = I × R. Power: P = V × I. In a series circuit current is common and voltage divides; in parallel, voltage is common and current divides.
- Voltage drop is calculated over the entire loop, so a 150 ft one-way run is 300 ft of conductor.
- NEC Article 725 governs Class 2 and Class 3 power-limited circuits. These must be kept separate from Class 1 and power conductors unless the code's specific mixing conditions are met, and cable markings (CL2, CL3, CL3P) matter.
- PoE budgets: 802.3af delivers about 12.95 W to the device, 802.3at about 25.5 W, and 802.3bt up to roughly 71 W at Type 4. Check the power sourcing equipment budget, not just the port rating.
- Supervised intrusion loops use an end-of-line resistor so the panel can distinguish normal, alarm, open, and short conditions. Normally closed contacts open on alarm; normally open contacts close.
- Wiegand is a legacy reader interface; OSDP over RS-485 is the modern, encrypted replacement.
- Cameras and controllers belong on a segmented VLAN with static addressing, NTP time sync, and no direct internet exposure.
Worked example
A 24 VDC camera draws 0.5 A at the end of 150 ft of 18 AWG copper, listed at 6.4 ohms per 1000 ft. Loop length is 300 ft, so R = 6.4 × 0.3 = 1.92 ohms. Drop = 0.5 × 1.92 = 0.96 V. The camera sees 23.04 V, a drop of about 4 percent. That is acceptable for most 24 V devices but close to a 5 percent design target; a 16 AWG run would cut the drop to roughly 0.6 V.
Traps that cost marks
Using one-way distance in the drop formula; assuming a PoE port's label equals delivered wattage; and treating Class 2 and Class 1 wiring as interchangeable. Also watch for questions that ask for the voltage at the device after a drop rather than the drop itself, and for series/parallel questions where one wrong branch changes every current value.