The lights inside our swimming pool keep blowing their bulbs

Swimming Pool Lights

The bulbs fitted to swimming pool lights for the amount of use and time they are switched on do not last as long as normal house lights, the reason is simple, they have not been fitted correctly and been commissioned.

Any electric inside the pool hall or near the pool on outdoor pools needs to meet the IEE Wiring Regulations, 17^th Edition. Basically the lights inside your pool are low voltage, normally 12 volts, but can also be as high as 24 volts for older installations. These lights are normally feed from individual lighting transformers that step down the normal UK voltage of 230 volts to the 12 volts needed for the pool lights and also provide isolation between the two electrical circuits.

So why do the pools lights blow?

Without getting too technical, each light has its own cable run from the transformer to a deck box on the pool side, where it connects to the pool light itself. We will assume that it’s the old style Certikin 300 Watt light, which at 12 volts needs to be supplied with 25 amps of current to generate the correct amount of light. The transformers normally come with different output terminals that provide voltages from 13 to 17 volts, but most installers connect the cables to the 13 volt terminal.

This is one of the reasons the pool lights can blow, as the light wants 25 amps to generate its 300 watts, but at 12 volts the restriction of the cable can cause a very large volt drop over a cable that is going to be up to 30 metres long. These cables are normally run around the outside the pool shell from the plant room housing the transformers, and this volt drop means that the voltage at the bulb will be 13 volts less this volt drop, which we have seen as low as 7 volts. This causes the cable to overheat and bulbs too blow as they are not working at the correct voltage.

What other reasons do lights fail?

Other reasons for pool lights failing are;

1. Only using a transformer to supply two lights when it’s not designed to do it, if the transformer has the capacity to supply two lights, connecting cables of different lengths can also cause problems.

2. Wrong sized cables, this is common due to the high cost of copper; cables are downsized and run warm and restrict the current.

3. Bad terminations between cable and the pool light.

4. Too high voltage can be worst than too little, each light needs to be balanced by a qualified electrician.

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