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With the Christmas Season fast approaching, we look forward to decorating our homes in the typical Yule Tide manner. The Christmas tree is the highlight of Christmas decorations. Fire hazards have been discussed in previous Leading Edge articles and Christmas tree lights will be concentrated on in this article. There are two common formats of Christmas tree lighting; the larger 1/2" bulb (socket size) and the smaller 1/4" mini-lightbulb size. The larger size bulbs are run in parallel and, therefore, supply 115 volts AC to each lightbulb. Frayed, cracked, or loose wire connections can result in high resistance overheating and/or limited short circuits resulting in possible ignition sources for fire. These larger size light strings are considered relatively safe provided the above signs of deterioration are detected and eliminated.

The design of the mini-light strings leaves much to be desired. Studies carried out by Walters Consulting Corporation have revealed numerous design deficiencies, many of which can cause fires.

The use of lower cost materials is largely to blame for such deficiencies. The two connector plates inside a mini-light socket are crimped into the ends of the wires and installed loosely. These plates can come loose and connect when the bulb is removed causing a short and sparks. Fires have reportedly been started in this manner. Also, the crimp connection of the connectors to the wires can come loose causing high resistance heating or short circuit. Variance of thickness of insulation on the conductors has also been observed making them more susceptible to deterioration resulting in possible limited short circuit. Furthermore, the brass inserts connected to the conductors in the plugs can come loose or fray resulting in high resistance heating leading to fire.

The design of the mini-light string bulb assemblies is questionable. The glass bulb is manufactured separately from the plastic insert which fits into the plastic socket on the string. This bulb has two wires which extend out its base and fit into two small holes in the base of the plastic insert. The wires are then wrapped around the outside of the plastic insert, such that they come in contact with connector plates inside the sockets. The glass bulb is not permanently connected to the plastic insert, therefore, the bulb can be turned freely when installed, allowing the wires to short. Since the bulbs are connected in parallel, voltage increases across the remaining bulbs intensifying brightness and surface temperature of combustibles have been measured on bulb surfaces when several bulbs in a strand are twisted.

Furthermore, the mini-bulbs come in 3,6,9 and 12 volt formats corresponding to 40, 30, 20 and 10 light strings. Since the bulbs are interchangeable a 3 volt bulb can be installed on a 12 volt, 10 bulb string resulting in four times the rated voltage causing it to glow brighter and hotter, thus compounding the problem. Ignition of combustibles has been achieved in tests conducted by Walters Consulting Corporation.

The mini-Christmas light strings have been approved by Canadian Standards Association (CSA), however, the replacement bulbs have not. Therefore, care must be exercised when using the mini-lightbulbs. Firstly, ensure that the light string bears the CSA mark. Secondly, carefully inspect the strings each year before use of damaged wiring, light sockets, and plugs. Thirdly, replace all failed bulbs with proper voltage bulbs. Finally, never replace the bulbs while the strand is energized.

If you abide by the above rules and use your common sense it will help ensure a safe and happy holiday season.

The information contained in this web site is intended for marketing purposes only. It is not all-inclusive, and does not fully describe the many and varied services that the company provides, nor does it completely describe the education, training, skills, or expertise of our staff.


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