In our daily life, almost all the items we used, being a computer, television, lift or vehicle we drive consist of some kind of electrical or electronics component inside. The operation of these devices could be severely affected by lightning activity or electrical switching events, as there are more than 2000 thunderstorms in progress at any time resulting in 100 lightning flashes to ground per second. In practice, any device using electricity will subject to surge damages induced from the lightning or switching of heavy load. Surge protection device (SPD) is added at the power distribution panel and critical process loop to prevent damage subsequently cause plant shutdown. There are many questions raised on the SPD. How can this small device protect the equipment from large energy release by the lightning? What is inside the device? How does it work? This paper provides comprehensive detail in revealing the science and engineering behind the SPD, its individual component characteristic and how does it work. The technical information presented is limited to surge protection on equipment; surge protection for building structure will not be discussed here.

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A modern process plant is controlled, operated and safeguarded by the sophisticated distributed control system or a programmable logic controller and an emergency shutdown system. This process plant's operation could be seriously affected by lightning, electrical switching, and power outrage. Lightning propagation can travel kilometers away, which has the risk of disturbing the control system's operation. The process plant's control system could damage when it is subjected to surges induced by lightning, power outrage, or heavy load switching. To protect equipment damage from these surges surge protection device is required. A number of the process plant uses flammable material for its production or during the manufacturing processes, explosive gas or vapor is released created an explosive atmosphere known as hazardous (Ex) area. Surge protection device mounted in the Ex area or used in the Ex control loop needs to be carefully selected to protect the equipment and at the same time, it does not become a source of ignition. This paper provides practical consideration and comprehensive detail in revealing the science and engineering behind Ex application on surge protection devices. The technical presentation is limited to equipment protection; structural protection against lightning will not be discussed here.

Intrinsic safety is one of the explosion protection techniques implemented in an industry where a flammable substance is present. It is a technique that reduces the electrical energy level at the hazardous area below the ignition curve so that it is not sufficient to initiate an explosion. In addition to limiting the energy to the field, the energy stored in the circuit and thermal ignition due to hot surfaces in hazardous areas must also be considered. Intrinsically safe is the preferred explosion protection method for instrumentation and control signals as it allows live maintenance, the use of an uncertified simple apparatus, and is applicable to all Zones. All intrinsically safe circuits must carry out a safety assessment and verify their compliance with intrinsic safety before implementation to avoid explosion. The verification process could be complex for mixed circuits and non-simple intrinsically safe systems; moreover, there has been much confusion for many years until the 4th Edition of the installation standard, IEC 60079-14, provided a clearer picture. This paper carries out an intrinsic safety verification assessment on a mixed circuit involving surge protection devices according to IEC and NEC standards. It also highlights the common mistake made by system designers when verifying the safety parameters.

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