The relationship between IEC 61508 and IEC 61800-5-2

These are two important standards that deal with the safety of electrical systems and frequency converters, respectively: IEC 61508 and IEC 61800-5-2. Here is a closer look at the safety guidelines for electrical systems and frequency converters.

How the standards compare

IEC 61508 and IEC 61800-5-2 both provide detailed guidelines for ensuring the safety and reliability of electrical devices and frequency converters used in a wide range of industrial applications.

But IEC 61508 “Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems” is a functional safety standard that establishes the principles and requirements for electrical systems to provide an adequate level of safety.

It is therefore applicable to industrial automation, energy, transportation, and consumer product manufacturing. IEC 61508 provides detailed guidelines on how to identify, analyze and reduce risks associated with electrical systems throughout the entire lifecycle of the system.

In contrast, IEC 61800-5-2 “Adjustable speed electrical power drive systems – Part 5-2: Safety requirements – Functional” is a specific standard for frequency converters used in variable speed electrical power drive systems.

It focuses on the functional safety of frequency converters, which are the electronic devices used to control the speed of an electric motor. IEC 61800-5-2 details guidelines for implementing functional safety in frequency converters to prevent accidents and ensure reliable operation.

How the standards correlate

IEC 61508 and IEC 61800-5-2 are closely related because, as mentioned, both focus on the functional safety of electrical systems. We have seen that while IEC 61508 has a broader field of application, IEC 61800-5-2 focuses specifically on frequency converters.

However, these standards complement each other and can be applied together to ensure an adequate level of safety in electrical systems using frequency converters. In this regard, one safety feature indicated by IEC 61500-5-2 is, for example, Safe Torque Off.

What is Safe Torque Off

The purpose of the Safe Torque Off function is to disable control of the electric motor so that it cannot produce dangerous output torque.

In fact, it is a safety measure that is often used in frequency converters and electrical drives to ensure the safety of operators and machinery.

The main goal is to reduce the risk of accidents related to rotating or moving machinery during maintenance operations or emergencies. When activated, Safe Toque Off cuts power to the electric motor, stopping its rotation immediately.

So Safe Torque Off may become a key function in achieving a tolerated risk level of a machine, and therefore its SIL certification may be required.