IP RATINGS – WEATHERPROOF OR WATERPROOF?

An Ingress Protection rating is given to a garden lighting product (garden light, transformer or junction box) to show its resistance to entry by physical objects and particles in the atmosphere and its resistance to water entering the enclosure or housing. It consists of two digits after the capital letters “IP” - the first digit is resistance to objects and particles and the second digit shows the resistance to water.

The first digit provides a measure of protection against solids - how dust or insect proof the product is:

The second digit measures protection against liquids – in practice this means that lights are weatherproof enough for outdoor use with a minimum rating of 4. Ratings of 5 and 6 means they are ok in areas where you are using a hosepipe (but not pointing a pressure washer directly at the light!). 7 is where lights start to become more than weatherproof – they can be regarded as waterproof for limited immersion in water – this rating was originally for marine fittings as a ship’s deck rolled into a wave. Only the 8 rating means the light is waterproof for use in ponds, bog gardens or riverside gardens prone to flooding. So if your lawn becomes very soggy for a while after heavy rain, make sure recessed lights are IP68 rated or provide drainage beneath and away from the underside of an IP67 light – a gravel-filled trench or tile drain along the cable route is often sufficient.

Ingress of water can still happen to IP68 lights if:

• Cables have been pulled loose in a sealed gland; this can happen if underwater lights have been fouled during weed removal in ponds or if lights have been carried by the cables during installation
• The cable gland is loose – tighten the nut around the cable gland to ensure a close seal around the cable
• The top plate is not fastened down both firmly and evenly, each screw being fastened down a turn at a time in diagonally opposite rotation (like a car wheel) with equal pressure on each screw fixing so the gasket is uniformly compressed and the top plate has not been distorted
• The lens or gasket are dirty when fitted so that soil or debris prevents a perfect seal and acts as a path for capillary action; if in doubt clean the lens with bathroom limescale remover to clean off any film.
• The gasket has not been fitted properly or has been damaged
• A light without a pre-fitted cable has not been installed properly with an IP68 gland and an HO7-RNF rubber cable – PVC cables are not suitable for such installations
• Water has been sucked along inside the cable from a joint or junction box which has not been properly waterproofed (a process called “wicking” caused by pressure fluctuations in lights as they heat up and cool down).
• Sealant materials such as silicon have been applied in the mistaken impression that this improves the seal, when in fact most silicon sealants do not bond sufficiently to be waterproof outside
• Lamps of an excessive wattage have been used - for example 50w underwater lights rely on water cooling and are limited to 35w lamps if not fully submerged. Lights which overheat as a result can expand and contract around the gasket area beyond their design limits and allow moisture to be sucked in

All exterior lights, especially IP68 lights, are prone to condensation inside if they have been fitted during weather conditions which mean damp air has been trapped inside; a few drops of condensation on the underside of a lens is often mistakenly exaggerated as water getting into the light on a larger scale. If this has happened, dry the interior of the fitting with tissue, then stand the light out of water facing vertically upwards with the lamp and lens fitted but without the top plate in place; switch the fitting on for 15-20 minutes so it warms up enough to dispel any moist air. Switch off and screw the top plate in position, having either waited for the fitting to cool to a temperature suitable for safe handling or wearing thermally insulated gloves.

Copyright 2008; Information based on products supplied by Lighting for Gardens Limited and is advisory only. The company accepts no responsibility for incorrect use or application of information given. Light fittings can become hot in use; exercise appropriate precautions. Exterior electrical installations should be undertaken by a qualified electrician.