Transients and surge protection considerations in electrical equipment — Offense and defense

The control and acceptance of electrical transients and surges on power-supply circuits, distribution networks, and electrical utilization equipment can be viewed in terms of the sports analogy of “offense” and “defense”. On the offense, power utilities and service providers need to control the transients that their power networks deliver to their customers, limiting transients to a maximum acceptable level. On the defense, electrical utilization equipment needs to tolerate transients up to the maximum levels that may be present at its point of installation, or if it cannot tolerate those maximum levels, protection such as surge protection devices or more robust overcurrent protection must be introduced to the electrical installation. Overvoltage categories are examples of expected levels of transients on power systems. From a product safety point of view, this paper explores the maximum levels of transients expected at the points of connection for electrical equipment, and describes customary practice and regulatory rules for tolerating or suppressing power transients for electrical utilization equipment.