All circuits have a minimum and maximum temperature range under which they can operate. Most security system circuits are designed to operate from −10 to 0 °F (−22 to −17 °C) on the low end to about 122 °F (50 °C) on the high end. Systems that are made to mil-spec specifications can handle temperatures up to 150 °F (60 °C).

Operating the electronics outside of these temperature ranges will result in malfunctions and ultimately damage to the electronics. This occurs most often in outdoor installations. Let me give you three examples:

The electronics may exhibit unreliability and is certainly likely to fail entirely in half its rated life (typically 7 years). What can you do about this?

Air-condition the enclosure or move the electronics inside an air-conditioned space. Wiegand wiring can run 550 feet (167.7 m) and dry contact wiring can span equal distances (use larger gauge wiring to assure good communications).

The card reader will almost certainly exhibit unreliability and will fail before its normally expected useful life (7 years). What can you do about this?

Mount the card reader onto a fiberglass junction box, which is then surface-mounted to the steel building surface. This will insulate the card reader from the high-temperature radiating steel surface.

At this temperature electronics may be expected to operate very poorly or to shut down completely. Depending on the construction, it may or may not operate again when restored to normal operating temperatures. What can you do?

Mount the Card Reader within a fiberglass enclosure that also includes a 7 W light bulb and a temperature sensor. The light bulb will maintain the enclosure within the normal operating temperature and the temperature sensor can be used to signal an alarm if the light bulb burns out, alerting maintenance to replace the bulb.

Humidity is a long-term and silent killer of electronics. Condensation is its quick-acting cousin.

Condensation occurs when humidity reaches its dew point; that is, when the air is so full of water vapor that it can no longer be supported as a vapor and it condenses back into liquid water. Condensation usually occurs when water vapor strikes a solid surface that is colder than the surrounding air. When this occurs, the water condenses onto whatever surface is near. As the water forms into droplets on the surface, it can conduct electricity, if that surface is an electrical or electronic circuit. When that occurs, the circuit can be short-circuited as electricity takes the path of least resistance (through the water droplets), bypassing resistors, capacitors, transistors, and integrated circuits. This forms unintended circuits that can apply unintended voltages and currents to electronics, damaging them permanently.

Humidity is the degree to which the air is filled with water vapor. As humidity percentages rise, so does the chance for long-term damage to electronics. As humidity forms near electronic circuits, it can trap dust, spores, bacteria, and other matter floating in the air, making them moist, and when they touch an electronic circuit they will settle there permanently. All of these things conduct electricity to a greater or lesser degree. Over time, they form a semi-conductive layer on the electronic circuit that can cause the circuit to malfunction and become damaged. The effect is cumulative, and although this can take years to accumulate, the result is certain.

The answer is to protect electronic circuits from humidity and condensation.

If you have ever twisted a paper clip into a straight line and then twisted it back again into the shape of a paper clip you may have found that the metal broke while bending. If not on the first try, then pretty much certainly after a few more tries. This is because of metal fatigue. The molecular structure of the paper clip is broken by repeated bending. This phenomenon also occurs on circuit boards, connectors, wires, and paper clips.

If an electronic circuit is placed into an environment with continuous to infrequent vibrations (say near an HVAC fan unit or elevator machine room), that circuit can be placed under stress each time it vibrates.

Over time, things can fail. The most common failure points include:

When circuits fail due to vibrations, they may fail either catastrophically or by exhibiting infrequent anomalies. Troubleshooting intermittent circuits is always difficult. When dealing with circuits in a vibrating environment, be sure not to rule out vibration as a possible culprit.

Any time that an electronic circuit is exposed to dirt accumulation, there will be problems. Any environment subject to the collection of dirt is also subject to humidity, and often condensation, insects, and possibly larger creatures. All of these are bad for electronics. Any of these issues can make electronics fail catastrophically or by an accumulation of intermittent problems over time.

Even if the electronics accumulated nothing but dirt, there would still be problems. Dirt itself is a semi-conductor and can change the behavioral properties of any electronic circuit.

It is surprising how many electronic circuits are exposed to insects, birds, snakes, and other creatures. Creatures like warmth in the winter (and sometimes other times too).

Electronic circuits make a wonderful place for nesting for small creatures and larger ones that can squeeze through a cabinet opening will go there for warmth. This is never good for the electrical or electronics circuits and is often also bad for the creature (see Figure 24.1).

You can prevent this on indoor cabinets by filling all of the holes in boxes with vent plugs. A vent plug is a small plug that goes into an electrical cabinet conduit opening hole constructed of a small screen with a frame that pressure fits into the conduit hole.

Outdoor cabinets should not have any holes on the top or sides as these can facilitate entry of rain and moisture.

One would not normally think that lighting could cause a problem for electronic circuits, but in some cases it can. Certain types of lighting (notably fluorescent and mercury vapor lights) operate by creating a plasma that reacts with a luminescent coating on the inside of the lamp. It is this reaction, rather than the plasma, that creates the light. But as a fluorescent lamp ages, the plasma it creates can become unstable. You may have noticed older fluorescent lamps that flicker like a flame licking the inside of the bulb. This condition can create variations in the plasma at twice the line frequency. This can create multipath reflections in adjacent circuits where the shielding of the circuit is poor (as is the case with most consumer and commercial quality circuits).

Most circuits assume that they will be operating in a stable electrical environment. When they encounter flickering fluorescent lamps nearby, the result can be unstable communications that can be a nightmare to troubleshoot.

It is best not to place circuits or run cabling close to fluorescent fixtures or any other light fixtures that create light by exciting a plasma.