30 Jun DIN Rail Risk Analysis
Canary HLE President,
Hazardous Locations industry expert
Over the years I have learned and applied many tips and advice from the countless Standards, Articles, and Manufacturer’s papers that I have read. Here is one that I would like to share about DIN rails and intrinsically safe barriers.
Leakage currents from power supplies, undetectable by human touch, can be enough to ignite certain explosive atmospheres. Therefore, intrinsically safe (IS) barriers must be isolated from the “dirty ground” and connected to a “clean ground”. This starts at the mounting (DIN) rail of the barrier and continues all the way to the isolated IS ground.
DIN Rail Risk Analysis
Intrinsically safe barriers are designed to prevent dangerous levels of energy that would ignite an explosive atmosphere. However, if the barriers are not correctly installed, the safety can be compromised. In most cases a DIN rail is the mounting system used for intrinsically safe barriers. DIN rails are constructed of different materials, examples being aluminum and cold rolled steel. In addition to being the mounting system, the DIN rail provides an intrinsically safe grounding system for each attached barrier. The barriers themselves typically have copper as the mounting/latch material for the intrinsically safe grounding system.
NOTE: When dissimilar materials come into contact with each other, a galvanic reaction may occur. Over time, this action will reduce the electrical grounding system between the mounting DIN rail and attached barrier, rendering the safety function of the barrier ineffective.
Some manufacturers alleviate this problem by employing a nickel-plated DIN rail. However, some explosive atmospheres (such as acetylene) will react to nickel causing the growth of explosive crystals (referred to as acetylide compounds). Therefore, a complete risk analysis should be undertaken prior to selecting the appropriate DIN rails used for the mounting of barriers.