NEMA is an acronym for National Electrical Manufacturers Association. This organization gives electrical component enclosures ratings — such as NEMA 4X — based on their protective qualities. NEMA ratings specify whether an electrical component enclosure is safe for outdoor use, and what type of environmental conditions it can withstand.
Watertight. Must exclude at least 65 GPM of water from 1-in. nozzle delivered from a distance not less than 10 ft for 5 min. Used outdoors on ship docks, in dairies, and in breweries.
It is often difficult and confusing for engineers to know what type of rating they need to look for when they desire to have a “waterproof” enclosure. There is a big difference between waterproof, water resistant, and other but not specific certifications. To help out, there are several rating systems that have been developed by several testing agencies that verify the results. Among these, the two best known are NEMA and IP. Today will deal only with the IP system.
HAZARDOUS AREA SENSORS CERTIFICATION Thermocouples and RTD Sensors are a source of Ignition Electrical equipment including temperature sensors for use in Hazardous Areas needs to be designed and constructed in such a way that it will not provide a source of ignition. This equipment should be fully tested and certified with a certificate of compliance issued by an Independent Authority.
Explosion Proof classification for a sensor/transmitter means that the housing has been engineered and constructed to contain a flash or explosion. Such housings are usually made of cast aluminum or stainless steel and are of sufficient mass and strength to safely contain an explosion should flammable gases or vapors penetrate the housing and the internal electronics or wiring cause an ignition.
likewise, no system is explosion proof if it contains non-explosion proof components
Instrument engineers are responsible for providing safe and appropriate instrumentation. To declare a system safe, simply because a single component is approved, is dangerous in more ways than one.
Installing a temperature sensor in a hazardous location requires more than an approved explosion proof connection head. To meet the safety requirements of FM, you must consider the complete system: including the sensor, the thermowell (if required and used) and the connection head.
Each component in the system must meet the code. For example, many thermowells are supplied with 1/2-14 NPSM threads for the sensor connection. FM dictates that to meet the requirements for explosion proof, a tapered thread is required.
A thermocouple consists of two dissimilar conductors in contact, which produce a voltage when heated. The size of the voltage is dependent on the difference of temperature of the junction to other parts of the circuit. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a temperature gradient into electricity. Commercial thermocouples are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures.