(The term “lamp” is used rather than “bulb” as garden lighting lamps are not “bulb” shaped)
Sooner or later the lampholder in 12 volt spotlights, steplights or underwater lights may need replacement. Most of these types of garden lights use MR16 or MR11 reflector lamps or halogen capsule lamps with G4 & GY6,35 lampholder. The numbers in these lampholder type codes refer to the distance between the pins, and many garden lights are fitted with a “universal” type lampholder which will accept both lamp pin spacings. The lampholder is the ceramic socket into which the lamp pins are pushed.
Lampholders may require replacement because they themselves or the cabling leading into them may have become damaged for various reasons;
- Moisture may have entered the light for various reasons (see IP ratings – weatherproof or waterproof?) and caused arcing (or sparking) between the lampholder contacts.
- During initial lamp fitting or subsequent lamp replacement the lamp pins may have been forced into the lampholder at an angle, damaging the lampholder contact surfaces. Lamps with bent pins may cause similar damage.
- Some lampholders do not have pierced metal foil over the lamp pin aperture, so that fitting a lamp for the first time will create the piercing through a mark on the lampholder front.
- A tool may have been used to make the piercing the first time a lamp has been fitted and this may have resulted in enlargement of the lamp pin aperture.
- Non-captive lampholders are ones which are not fixed to the body of the light. They are normally fixed onto the end of the wires using push-fit ferrules or soldered wire-ends during original manufacture. If the lampholder is pulled out from the light too roughly when the lamp is originally fitted or subsequently replaced, then the wires can be pulled partially out of the back of the lampholder or the wires can be stretched slightly: this results in bare wire at the back of the lampholder as the insulated section is pulled away from it: arcing (or sparking) between the exposed wires can then happen, especially if there is some moisture in the fitting: condensation is enough to make this happen if the lights were lamped on a damp day and not run for a while with the top loosely fitted to dry out any moist air inside before the top is tightened down.
Replacement lampholders are available to address this repair requirement. Most original equipment lampholders are designed for factory insertion of wires using a special machine, and this can be a difficult task on site. Replacement lampholders usually used for lighting repair fall into two types: lampholders with pre-fitted wires already inserted into them and lampholders with screw terminals.
- Lampholders with pre-fitted wires do not have to be the same size or shape as the original in lights with non-captive lampholders, though they must have the same fixing centres if they are to be fitted to lights with “captive” lampholders – those which are fixed to the body or stem of the light. The connection of the pre-fitted wires to the original wiring must be made with ceramic “screwits” (otherwise known as “wire nuts”) or ceramic terminal blocks. Ceramic products must be used to with stand the heat of the lamp inside the light: plastic parts must not be used as they will quickly fail in this type of application.
- Lampholders with screw terminals are easier to fit, though they must have the same fixing centres if they are to be fitted to lights with “captive” lampholders. For non-captive lampholders, all that is necessary is to cut the wires immediately behind the old lampholder to leave the wires as long as possible. If the wires are charred by arcing then cut them back to just beyond the charred section and strip about 5mm of insulation off the wires to allow them to be fitted into the new screw-terminal lampholder. If for any reason the wires have been cut back so they are too short to be fitted directly into the lampholder screw terminals, then the best solution is usually to use lampholders with pre-fitted wires and connect them to the existing wiring with ceramic "screwits" or ceramic terminal blocks. In small fittings single rather than double terminal blocks may more easily fit inside, though the most compact solution is to use ceramic "screwits".
Copyright 2014; 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.