Could Help Desk recommend the qualities of cable conditioners or surge arresters for an access control solution we’re planning? We have been using gear recommended by an electrical wholesaler and on a number of occasions our power supply has been flawed. Are there specific numbers we should be looking for?

A: Take a look at the IEEE 587 standard – it will outline all you need to know in relation to surge arrestors and line conditioning. Pretty obviously, an appropriately rated surge protection device installed in parallel with the building’s main supply which is supported by a smaller surge protection device for the local security system is what you’re looking for.

The capabilities of the surge protection solution for the local security system – access control or CCTV – should include fundamentals like no moving parts, a metal oxide resistor providing high energy resistance, a ferroresonant design and high speed leading edge design.

You also want something that offers isolation primary to secondary sides, as well as offering at least 125 per cent of full load capacity. Go for +/- 1 per cent output volts at 85 per cent load, with -25 per cent to 15 per cent nominal input volts. Also important is a voltage change of load change of +/- 3 per cent for 3 cycles and 95 per cent correction for 2 cycles.