PLCs are well built and rugged, but they are still relatively easy to damage on the factory floor. As a result, enclosures are often used to protect them from the local environment. Some of the most important factors are listed below with short explanations.

Dirt - Dust and grime can enter the PLC through air ventilation ducts. As dirt clogs internal circuitry, and external circuitry, it can effect operation. A storage cabinet such as Nema 4 or 12 can help protect the PLC.

Humidity - Humidity is not a problem with many modern materials. But, if the humidity condenses, the water can cause corrosion, conduct current, etc. Condensation should be avoided at all costs.

Temperature - The semiconductor chips in the PLC have operating ranges where they are operational. As the temperature is moved out of this range, they will not operate properly, and the PLC will shut down. Ambient heat generated in the PLC will help keep the PLC operational at lower temperatures (generally to 0°C). The upper range for the devices is about 60°C, which is generally sufficient for sealed cabinets, but warm temperatures, or other heat sources (e.g. direct irradiation from the sun) can raise the temperature above acceptable limits. In extreme conditions heating, or cooling units may be required. (This includes "cold-starts" for PLCs before their semiconductors heat up).

Shock and Vibration - The nature of most industrial equipment is to apply energy to change workpieces. As this energy is applied, shocks and vibrations are often produced. Both will travel through solid materials with ease. While PLCs are designed to withstand a great deal of shock and vibration, special elastomer/spring or other mounting equipment may be required. Also note that careful consideration of vibration is also required when wiring.

Interference - Electromagnetic fields from other sources can induce currents.

Power - Power will fluctuate in the factory as large equipment is turned on and off. To avoid this, various options are available. Use an isolation transformer. A UPS (Uninterruptable Power Supply) is also becoming an inexpensive option, and are widely available for personal computers.

A standard set of enclosures was developed by NEMA (National Electric Manufacturers Association). These enclosures are intended for voltage ratings below 1000Vac. See NEMA Enclosures shows some of the rated cabinets. Type 12 enclosures are a common choice for factory floor applications.

NEMA Enclosures