Wiring Basics 5

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Wiring Basics 5

What are Motion Detectors

Motion DetectorMotion detectors are basically devices that detect motion within its field of view. There are many devices that accomplish this such as ultrasonic, microwave, passive infrared, photo-electric beams and cameras. Some manufacturers are making devices with "pet immunity" for families with small pets. By far most of us think in terms of microwave and passive infrared when we talk about motion detectors. As a matter of fact most manufacturers are combining the benefits of both technologies into a single unit. This has significantly decreased the rate of false alarms over that of the single technology. These not only require motion but also look for a heat source to generate a detection. When the PIR unit detects a movement of heat in the area, it then looks to the microwave part of the unit to confirm the movement. Both must register the movement to trip the alarm. This is why the placement of these devices should be well thought out and tested prior to the final installation.

Placement of these devices should be made so that potential movement is across the face of the detectors, rather than toward or away the units. The devices are much more sensitive to these lateral movements. Also refrain from having the units looking directly at heating or air conditioning ducts and large windows. Ceiling mount units are great for this because they ensure movement is across the face of the unit. However, wall mounts and corner mounts are also available.

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Wiring Motion Detectors

Motion Detector WiringMost motion detectors require external power, a set of contacts for signaling detection and some have 24hr tamper circuits to avoid removal or tampering. These units will require 4 to 6 conductors for operation. 2 for power, 2 for the relay inside (contacts) and 2 for the tamper circuit, if used. Most control panels provide for Aux power to different detection devices and will be labeled as such. Observe polarity when hooking up these devices (+ or -). The devices will have 2 or 3 terminals for zone hook up. The N.C. contact and the common contact should be used for normally closed circuits (Recommended) and the N.O. and common for normally open circuits. The final set of wires is the 24hr tamper zone which is normally closed with the cover secured on the unit. I want to point out something here. Powered devices such as motion detectors should be placed on a zone by themselves for ease of maintenance and troubleshooting. Imagine coming home and finding an alarm has occurred and when checking the alarm panel it indicates "zone 5 motion detectors". If you had 3 or 4 motion detectors on that zone, you would not know which device(s) you are having problems with. Trouble shooting becomes a nightmare.

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What are Smoke Detectors

Smoke DetectorThese are devices designed to detect smoke, usually from smoldering fires and some are equipped with fixed heat detectors. More and more home owners are incorporating fire protection within their home security systems. There are 2 basic types of smoke detectors in use today. They are ionization and photoelectric detectors.

Ionization detectors use a very small amount of radioactive material (Americium-241) located inside a chamber that contains negative and positive and plates. Under normal conditions the radioactive material allows current to flow inside the chamber, but when small smoke particles enter the chamber they disrupt this flow, which in turn causes the alarm to activate.

Photoelectric detectors use a light source and a photocell for a detector. These elements are arraigned inside a chamber so that under normal conditions the photocell does not detect the light. When large smoke particles, from a smoldering fire enter the chamber they reflect the light onto the photocell which in turn causes the alarm to activate.

Remember smoke detectors are always on regardless of whether or not the alarm panel is armed. This is very comforting for me to know my family is always protected and will be warned of impending danger.

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How to wire Smoke Detectors

Smoke Detector WiringSmoke detectors are manufactured in a 2 or 4 wire configuration. In the 2 wire configuration these detectors use the same 2 wires for power and to signal an alarm. The 4 wire version uses 2 wires for power and 2 wires for signaling an alarm. Which wiring configuration that you use will depend largely on the control panel being used. If your panel supports the 2 wire configuration, use 2 wire smoke detectors because they are much easier to install. Also you will not need the more costly 4 conductor wire. The power supervision relay shown in the bottom portion of the diagram to the left, is only required in U.L. installations. Always use "Fire Wire", a wire specifically designed for use in fire detection devices. Remember smoke detectors use N.O. contacts and E.O.L. resistors are always required for line supervision.

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Where should I locate Smoke Detectors

Smoke detectors should be located on the ceiling at least 6 inches from any walls. When mounting them on a wall they should be installed between 4 and 12 inches down from the ceiling. Do not mount smoke detectors in areas of high humidity or stagnant air flow. Smoke particles must be allowed to freely enter the smoke chamber. You should install smoke detectors inside each bedroom, family room, living room and on every level of the home (including basement). You should avoid placing smoke detectors in kitchens, bathrooms and attics to prevent false alarms.

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Continued on Wiring Basics 6 page.