Putting electrical equipment in a hazardous location is a big deal. Choosing the wrong sensor turns from expensive to life threatening. So how do you select the right level sensor or pressure transmitter?
You have to understand hazardous locations.
This is even difficult for many who deal with hazardous locations on a day-to-day basis. If you’re ever confused about hazardous location, particularly the finer details, we can help. Let’s start with defining a few different marks you’ll see on hazloc certified sensors:
Explosion Proof (XP) is descriptive of a sensor that is contained within a housing that is strong enough to contain a flame or an explosion. This method is used where it is impossible to reduce the electrical circuit energy. This is the case with sensors that require more power, or with other equipment such as electric motors.
Intrinsically Safe (IS) describes a sensor that is designed and wired to work on such a low current and voltage that it cannot possibly ignite flammable material. By limiting the energy available within the defined hazardous area, electrical equipment can operate safely even amid hazardous mixtures of gasses, dust, and metals.
This is a very basic and important distinction. Many environments require intrinsic safety, and many sensors can do no better than explosion proof, due to their current and voltage needs. Make sure you understand the needs of your application before you select sensors.
One of the most striking differences is how the two types of sensors are wired. When there are no application requirements that demand one over the other, this will play a big role in which option you select.
Explosion proof wiring requires conduit and seals. These are to isolate the circuit from hazardous gases. A seal is a fixture on the conduit that lets you pour in sealing compound. This prevents the gases from flowing into the conduit and gaining access to uncontrolled areas.
Even if the circuit did ignite a hazardous mixture that made its way into the explosion proof wiring, the housing and conduit can contain the explosion. Any escaping hot gasses will be cooled enough so that they would be incapable of igniting any of the hazardous mixture outside of the explosion proof conduit or fixtures.
Intrinsically safe wiring is much easier. There is usually no need for the conduit and seals, but you will need an intrinsically safe barrier. This device is wired between the sensor and the power source. It serves to block the power source from sending too much to the sensor.
It is still possible that gases may be funneled from the hazardous area to an electrical panel in a non-hazardous area via an intrinsically safe sensor. So cable glands and seals may need to be considered but they are of lighter construction, as they are not required to cool exploding gases – only to prevent the flow of gases.
As you might suspect, explosion proof wiring is typically much more expensive than intrinsically safe wiring. Keep this in mind as you choose sensors and establish protocol.
Another very important distinction between explosion proof and intrinsically safe sensors is where their use is permitted. There are three zones of hazardous locations that determine the level of protection:
- Zone 0 means that the area is constantly or often hazardous
- Zone 1 means that the area is occasionally hazardous
- Zone 2 means the area is rarely or temporarily hazardous
There are many methods of protection that can be used to make a sensor safe in a hazardous area. Most methods will allow the sensor to be installed in areas classified as Zone 1 or 2. However, only intrinsically safe (ia) and encapsulated devices (m) can be used in Zone 0 locations.
If you’re using the division system, there are restrictions on explosion proof sensors as well. A good rule of thumb is to compare it to the zone system and stick to intrinsic safety whenever the area would be considered a Zone 0 location.
This will certainly have a bearing on which type of sensor you choose. Make sure you are very careful to follow the rules. If you’re not sure, ask someone who knows.
Reach out to us if you have any questions. We’re happy to help you get the best sensor for your application under any circumstances.