May 11, 2020 by Emmanuel Ikimi
Circuit protection is a vital consideration in factories and manufacturing plants that helps to ensure the safety of personnel working on-site while protecting industrial equipment and assets from damage due to electrical and fire hazards.
Sound knowledge of industrial safety standards and proper circuit protection devices allows engineers to ensure electrical safety and compliance at all time
Industrial facilities are some of the most challenging environments for ensuring electrical safety for the following reasons:
Ambient temperatures in industrial environments such as chemical processing plants, food and beverage plants, metal fabrication, and pharmaceutical industries are significantly higher than in commercial and residential facilities.
Process temperatures easily exceed 100°C (212°F). Higher temperatures at industrial facilities impact the safety and reliability of electrical systems and machinery.
Industrial machines such as electric motors, air compressors, chiller units, and heating elements consume more power from the grid than household and commercial electronics.
Consequently, the risk of voltage transients, overload conditions, and short circuits are significantly higher. These hazards can compromise the safety of workers and the reliability of equipment without adequate circuit protection.
Electrical devices and equipment utilised in combustible areas, such as refineries and chemicals processing plants are at significantly higher risk of combustion due to sparking and heating effects in internal electronics and electrical wiring. Electrical fires can result in electrocution or cause irreparable damage to industrial machines.
Overload protection devices on an electrical control cabinet at a plant.
In Europe, the most recognised standard regulating the use of electrical equipment in industrial facilities is the Low Voltage Directive (2014/35/EU) by the European Union.
The equivalent in the United States is the National Electric Code (NEC). However, in the U.S, states, counties, or municipalities have their unique provisions governing electrical safety.
For electrical engineers in the U.S, NFPA 70E-2018: Standard for Electrical Safety in the Workplace provides standards for employees to minimise their risk of exposure to electrical hazards in the workplace such as electric shock and fire outbreak.
Similarly, the NFPA 79-2018: Electrical Standard for Industrial Machinery covers circuit protection for industrial machinery, to prevent electrical hazards and fire.
Circuit protection devices help to protect industrial equipment and wiring from harmful current and voltage levels that could result in electrical fires, arcing, electric shock, and melting of conductors and PCB components. The following are some of the most vital circuit protection devices utilised at industrial facilities.
Industrial fuses are overcurrent circuit protection devices that have higher current-limiting capacities than fuses intended for household appliances. For example, an industrial fuse can be rated up to 600V (35A to 60A). Like standard fuses, industrial fuses are non-reusable - therefore they must be replaced after a fault.
A circuit breaker is an overcurrent protection device for automatically interrupting the flow of electric current to a device when a fault occurs. Unlike one-time fuses whose internal conductors melt to open up the circuit, circuit breakers utilise a bimetallic strip and are reusable by manually resetting the device.
Various types of circuit breakers are employed at industrial plants, depending on voltage requirements, e.g., low-voltage industrial circuit breakers, high-voltage industrial circuit breakers, and magnetic industrial circuit breakers.
An inrush current limiter (ICL) is an electronic component that prevents damage to primary circuit protection devices such as fuses by limiting the inrush (input surge or switch-on surge) current flowing through a line.
ICLs consist of resistors or Negative temperature coefficient (NTC) thermistors. NTC thermistors are disk-shaped devices having a low resistance at a high temperature with power dissipation properties to limit the supply voltage before it reaches the protected circuit. Fixed resistor ICLs utilising standard resistors are relatively cheaper but less efficient.
Overcurrent protection devices.
Surge protection devices (SPDs) provide overvoltage protection to various sections of electrical power supplies at industrial facilities. Transient voltages (voltage spikes) commonly occur due to poor power quality, lightning strikes, and operation of electric motors etc.
Without adequate protection, transient voltages can degrade cable insulation or damage equipment. SPDs utilise surge protection elements such as metal-oxide varistors (MOVs), spark gaps, and Zener diodes to clamp dangerous supply voltage. They are commonplace in industries such as breweries, refineries, and wastewater treatment plants.
Lightning protectors help to protect industrial equipment from power surges due to lightning strikes. Industrial buildings with high peaks are susceptible to lightning due to the large surface areas that often contain metal structures.
Lightning strikes can produce surge voltages up to 1 billion volts and surge currents of up to 200kA. Lightning protectors consist of metal rods (made of copper or aluminium) mounted on the peaks of buildings and associated elements that provide a low-impedance pathway to a ground rod buried deep into the earth.
Circuit protection is critical for ensuring the safety of workers and minimizing the risk of hazards at industrial facilities. Electrical safety is particularly essential in industrial environments owing to higher temperature operation, higher power requirements, and an increased risk of combustion.
Electrical safety standards in Europe and the U.S. provide guidelines for overcurrent/overload and surge protection in industrial applications. Electrical engineers must utilise circuit protection devices to adequately protect electrical devices, machinery, and associated wiring.
