A concern with all post installations and the increased use of passive safe yielding and softer material posts is the possibility of roadside structures becoming live where electrical cables have been exposed. In the event of post impact or damage, protection from live electrical cables must be built into the complete passive safety installation. Requirements for electrical installations are covered in BS7671:2008 and IEE wiring regulations and have also been addressed in NA8 of the National Annex to EN12767 in the UK.

In short consideration must be given to physical cable disconnection and electrical isolation where both post and environment become voltage free after impact. This safety measure concerns not only the occupants of the vehicle involved in a collision with a post or column but also the emergency services personnel who attend the road traffic accident and the subsequent maintenance operatives who manage and repair the post and site.

The RETENTION SYSTEM can be combined with the use of passive safety posts, cable disconnection plugs and Safety Isolation Systems (SIS) to provide a complete passive safe installation.

IPL group promote the use of the SIS electrical isolation system for both passive safety applications and standard post installations. With this system each post and column has an impact sensor connected to a monitor board forming a closed electrical circuit. When activated (by damage or vehicle impact with the post) the impact sensor creates an open circuit and the monitor board remotely trips the associated circuit breakers. In tests this system will isolate the electrical supply between 80 and 140 milliseconds. In addition the monitoring board can also send out an activation output to a remote monitoring system to inform the local authority or operators of a post knockdown.

The SIS system is available in three basic versions to suit lighting columns, electrical posts or traffic signal applications. The impact sensor is attached to the post and utilises proven technology from the automotive industry. The monitor board and circuit breaker is designed per customer and post application. It can be din rail mounted (suitable for street lighting and signage), 3Urack mounted (suitable for traffic signals) or located in an independent roadside pillar.

When installed with a passive safety certified traffic signal post or lighting column the SIS activates isolation within 0.2 seconds and is fully compliant with electrical wiring regulations and EN12767. It is suitable for all available makes, types and post sizes and can be combined with cable disconnection plugs and the RETENTION SYSTEM for a comprehensive passive safe installation.

The SIS electrical isolation system can also be used on standard (non-passive safe) post installations. In conjunction with the RETENTION SYSTEM, it offers improved maintenance and safety benefits and allows individual traffic signals or other electrical posts to be isolated with the remaining posts live and operational.