• • • CIRCUIT PROTECTION • • •
Electrical installations must manage inrush current, for example, using circuit breakers
Eliminating inrush current in
electrical installations Inrush current, the large initial spike of current drawn by electrical devices when they are first switched on, is a recognised problem for many types of electrical equipment, and must be managed to guarantee the safety and long-term reliability of any installation
By Darrel Kingham, CEO at power electronics innovator, Pulsiv
What is inrush current? As the name suggests, simply put, inrush current is the large surge of current that enters an electrical device when power is first applied. Although it only occurs for milliseconds, inrush current can typically be 40-80x higher than the steady-state operating current for which a system may have been originally designed. This is particularly challenging where multiple units are connected and powered-up simultaneously. For example, for LED light installations, server racks in data centres, EV charger stations, alarm or air conditioning systems, or in scenarios where future expansion is possible. If ignored, the consequences can be catastrophic. Inrush current can lead to
blown fuses, damaged circuit breakers, welded relay contacts and major service interruptions.
What causes inrush current? All legacy AC to DC power supply designs contain energy storage components: capacitors, inductors and transformers that naturally draw significant amounts of energy during the start-up phase. Traditional power electronic circuits provide a low resistance path that allow large currents to flow. Think of it like trying to push a car. To begin with, a huge amount of energy is needed to move it, but less is required once there’s some forward momentum. Steps must be taken to avoid potential negative consequences in systems exhibiting this behaviour.
Figure 1. What is inrush current?
36 ELECTRICAL ENGINEERING • JULY/AUGUST 2025
electricalengineeringmagazine.co.uk
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