Security, Access Control, and CCTV Systems
Alarm sensing and zones
Security systems use intrusion detection devices such as PIRs, dual-technology detectors, door and window contacts, glass-break detectors, and shock sensors. A normally closed contact zone is supervised with an end-of-line resistor at the far end of the loop; placing the resistor at the panel leaves the loop untested for a short. PIRs respond to infrared energy and require stable temperature and proper masking; dual-tech units require both PIR and microwave agreement to reduce false alarms.
Access control and life safety
A reader, controller, door position switch, request-to-exit (REX) device, and lock make a basic door. Fail-safe locks unlock on power loss (maglocks); fail-secure locks lock on power loss (many strikes). Free egress cannot depend on the reader: a mechanical release or REX is required, and the door must comply with local fire and building codes. ADA and fire code limits on opening force, hardware height, and delayed egress apply.
CCTV and storage
IP camera design considers resolution, lens angle, minimum illumination (lux), wide dynamic range, bit rate, and retention. A 4 MP camera does not automatically identify a face at 100 ft; pixels on target matter. Storage is calculated from bit rate, camera count, and retention days.
Worked example
Eight cameras record at 4 Mbps each, 24 hours a day, for 30 days. One camera: 4 Mbps = 0.5 MB/s. 0.5 × 86,400 s = 43,200 MB, or 43.2 GB per day. Eight cameras: 345.6 GB/day. Thirty days: 10,368 GB, or about 10.4 TB. Add 20 percent overhead: 12.4 TB. A 16 TB usable array covers the job; a 10 TB array does not.
Delaware licensing
Alarm businesses and alarm technicians are licensed through the Delaware State Police alarm licensing program; electrical work falls under the Board of Electrical Examiners. A security installer should not assume that an electrical or alarm credential covers fire alarm, access control, or CCTV work outside its scope.
Traps
- Reversing fail-safe and fail-secure.
- Putting the EOL resistor at the panel instead of the end of the line.
- Omitting a REX or mechanical egress release.
- Sizing storage from resolution alone without bit rate and retention.
- Ignoring minimum illumination and lens field of view.