NATIONAL FOREWORD

This Indian Standard (Part 17) which is identical with ISO 7240-17 : 2009 ‘Fire detection and alarm systems — Part 17: Short-circuit isolators’ issued by the International Organization for Standardization (ISO) was adopted by the Bureau of Indian Standards on the recommendation of the Fire Fighting Sectional Committee and approval of the Civil Engineering Division Council.

This standard is published in various parts. Other parts in this series are:

Part 2 Control and indicating equipment

Part 3 Audible alarm devices

Part 4 Power supply equipment

Part 5 Point-type heat detectors

Part 6 Carbon monoxide fire detectors using electro-chemical cells

Part 7 Point-type smoke detectors using scattered light, transmitted light or ionization

Part 11 Manual call points

Part 12 Line type smoke detectors using a transmitted optical beam

Part 15 Point type fire detectors using scattered light, transmitted light or ionization sensors in combination with a heat sensor1)

Part 16 Sound system control and indicating equipment

Part 20 Aspirating smoke detectors

Part 22 Smoke-detection equipment for ducts

Part 23 Visual alarm devices

The purpose of short-circuit isolators is to limit the consequences of low-parallel-resistance faults between the lines of a transmission path of a fire detection and alarm system. This is normally achieved by connecting the transmission path in a loop configuration, separating sections of the loop with short-circuit isolators and introducing a means of detecting the presence of a fault, if its consequences (for example, reduction in the line voltage) jeopardizes the correct operation of components on the transmission path. The faulty section of the loop can then be switched out, between a pair of short-circuit isolators, allowing the rest of the loop to continue to function correctly.