{"id":8525,"date":"2025-06-24T14:26:29","date_gmt":"2025-06-24T12:26:29","guid":{"rendered":"https:\/\/lorit-consultancy.com\/en\/?p=8525"},"modified":"2025-06-24T14:57:17","modified_gmt":"2025-06-24T12:57:17","slug":"the-class-4-power-supply-functional-safety-challenge","status":"publish","type":"post","link":"https:\/\/lorit-consultancy.com\/en\/2025\/06\/the-class-4-power-supply-functional-safety-challenge\/","title":{"rendered":"The Class 4 Power Supply Functional Safety Challenge: High Stakes at High Voltage"},"content":{"rendered":"

We have recently written several blogs exploring the overleap between functional and non-functional safety \u2013 including a closer look at IEC 60664<\/a><\/strong> in \u201cThe Fountain of Knowledge\u201d<\/a>. In this blog, we shift focus to the functional safety challenges associated with Fault-Managed Power Systems (FMPS)<\/strong> \u2013 also referred to as Class 4 power systems in the US National Electrical Code (ANSI\/NFPA 70)<\/a>. Rather than discussing their technical advantages, we focus here on the crucial safety task of preventing electrocution in the event of someone touching a hazardous voltage.<\/p>\n

Delivering Power Safely: What FMPSs Bring and What They Risk<\/h2>\n

Fault-Managed Power Systems offer many advantages in delivering power over long distances, including increased efficiency<\/strong> and the use of smaller gauge cables<\/strong>. Fig. 1 illustrates a typical block diagram. Both the transmitter and receiver incorporate a mechanism that switches the power supply to a safe level within an appropriate timeframe if a leakage current is detected \u2013 for example, when someone touches a hazardous voltage.<\/p>\n

\"Figure
Figure 1: Typical FMPS Application<\/figcaption><\/figure>\n

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The first challenge in achieving the safety goal of reaching a “safe level” is defining what safe actually means. This is where the consideration of ventricular fibrillation comes into play.<\/p>\n

Managing the Risk of Ventricular Fibrillation<\/h2>\n

The primary objective of FMPSs is to avoid ventricular fibrillation (VF)<\/strong> \u2013 in other words, a hazardous electric shock. In addition, the energy level must not be so high that a person is unable to let go of the cable if touching a hazardous voltage.<\/p>\n

Ventricular fibrillation (VF) introduces several important safety considerations. Typically safety standards such as IEC 60601<\/strong><\/a> ensure touch or leakage currents remain below 0.5 mA in a single fault conditions (SFC) as a key goal. However, there are more factors than the current alone to consider:<\/p>\n