Ex Protection Options for Deploying Wireless into Hazardous Areas

If you want to deploy wireless devices into hazardous areas, you have two options:

• Option one: Buy a wireless device that has been fully certified by the manufacturer to relevant Ex standards
• Option two: Buy a pre-certified Ex wireless enclosure solution to house your preferred hardware

The likelihood is that your chosen wireless device does not hold the required hazardous area certification. This is typically because it is a specialised market and new technology is not often made available as a hazardous area version when it is first introduced to the market. Furthermore, technology companies rarely develop a hazardous area version of their devices because the market size is too small for their business model.

The most likely option for end users is to use an Ex certified enclosure system. Without this solution you will not be able to install the wireless technology in your hazardous areas on site.

It is worth knowing a little more about the different Ex protection options available and which hazardous zones they are suitable for as this will help you make an informed decision when choosing your wireless enclosure system supplier.

Firstly, when you are considering Ex protection concepts for your wireless device there are several concepts available:

• Protection by encapsulation (containing an explosion)
• Protection by keeping a flammable gas or dust out
• Quenching a flame
• Limiting energy (to avoid spark or thermal ignition
• Installing the wireless device in a safe area and an Ex rated antenna in the hazardous area

There are various protection types that cover all the above, but the most common seen in industrial and process industry settings for wireless devices are Ex d and Ex n.

Image caption: Typical Ex d and safe area installation

Ex d – IEC 60079-1 (Typical Zone: 1, 2, 21, 22 and Division 1)

An Ex d enclosure is designed to contain an explosion and stop any flames, sparks and hot gases from escaping into the surrounding atmosphere should an internal explosion occur. In addition, an Ex d enclosure protects the fitted equipment against external moisture, dirt, dust or water.

Read more about Ex d enclosures here

Electrical equipment, such as a wireless radio device, has the potential to operate with potentially hot surfaces, which could cause an explosion if not housed correctly with the relevant Ex protection.

Often referred to as ‘flameproof’ or “explosion-proof”, an Ex d enclosure also includes what is known as a flame path. The flame path design can vary depending on the construction of the Ex d enclosure system.

A flame path is a gap within the enclosure that, if an internal explosion occurs, ensures that by the time the flame has reached the end of the flame path it has been starved of oxygen or cooled down to such an extent that nothing, but air propagates from the explosion. The flame never escapes the enclosure and so cannot ignite an ambient gas.

Some flameproof boxes have flame paths that operate surface to surface, like a flange touching a joint, whereas others like a typical IIC gas group enclosure have a lid that screws into the body of the enclosure. In these enclosures, the flame path is in the thread, forcing the flame to move in and out of the thread quenching the flame.

Ex d enclosures are usually heavy and bulky due to the requirements of the Ex standard.

Image caption: iWAP107 Ex d wireless enclosure with lid open to show wireless access point mounted to internal chassis.

Ex nR – IEC 60079-15 (Typical Zone: 2, 22 and Division 2)

An Ex nR or restricted breathing enclosure removes the fuel element of an explosion by stopping any flammable gasses entering inside the enclosure. In doing so, potentially explosive gases never meet hot surfaces or an ignition source potentially present inside the enclosure.

Read more about Ex nR enclosures here

Restrictive breathing enclosures are only certified to Zone 2 hazardous areas, where the area is considered safe in normal operation with flammable gases only present in fault conditions.

A Ex nR enclosure typically has the following characteristics:

• Lightweight metallic or non-metallic construction
• Designed to prevent flammable gases entering
• High ingress protection levels
• Tightly sealed

Image caption: iWAP XN3 range of Ex nR wireless enclosures

Ex i – IEC60079-11

The Ex i intrinsically safe protection concept is not available as an enclosure, it is designed into the electrical equipment so that the finished certified device is safe in its own right. This is achieved by limiting the amount of power fed into a circuit to avoid ignition by hot surfaces as well as limiting the amount of energy storage which could lead to spark ignition. This concept is specifically used in the context of Ex wireless enclosure systems as a method of protecting the RF output of the radio equipment rather than the radio device itself. Installing the radio equipment in a safe area and the antenna in a hazardous area is the lowest cost solution as it does not require the use of a certified enclosure. If connecting the antenna to an uncertified radio you must consider that AC or DC could pass through the radio under a fault condition. If this was fed into a standard antenna this could lead to an unsafe condition.

Learn more about intrinsically safe isolators

Therefore, there are two distinct options for this use case. Option one uses an intrinsically safe RF isolator between the antenna and the radio, see Figure 1, which limits any hazardous fault current that could pass into the hazardous area mounted antenna. This method of protection allows the use of standard antennas in most types of hazardous area. Option two is to use an Ex antenna where the antenna is designed and certified to the Ex standards. This would typically be Ex d or in some cases Ex e (Increased Safety).

For more information or to see how Extronics can help you with your hazardous area wireless connectivity, please contact a member of our team on +44 (0)1606 738 446 or email us at info@extronics.com.