RCD Trends

It must be said that VD and VI RCDs have made an enormous contribution to electrical safety worldwide, and both types will continue to play this vital role in the future. There is no question of one type being completely displaced by the other. However, the use of VD RCDs has increased enormously over recent years because they offer some advantages over VI types, and this is why most major manufacturers now produce VD and VI types. The main developments and trends over recent years are as follows.

SPRCBOs = a substantial increase in their use because of the trend to provide more RCD protection on subcircuits. These are generally VD types.

Type B RCDs, which can only be produced in electronic (VD) form.

Compact RCBO or mini RCBO now available in an 18mm MCB package, and can only be produced by VD technology.

ARD = Auto Reclosing RCD. These rely on VD technology and are used in remote locations or in cases where restoration of power is very important. The RCD trips on a first “fault” which may turn out to be transient, but recloses after a time delay and will remain closed if the fault no longer exists.

POP = Protection against Overvoltage at Power frequency. A dreadful acronym, but this device trips automatically under temporary overvoltage (TOV) conditions and protects equipment from damage that could be caused by TOVs.

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About the author:
Pat Ward is managing director of Western Automation R & D based in Ireland. The company is a specialist designer and manufacturer of RCD products. Pat has been an active member of technical committees in ETCI, IEC and CENELEC since 1991 and has been involved in the drafting of several international standards for RCDs & RCMs. He has also participated in working groups within IEC addressing problems of reliability and EMC requirements for RCDs.