There are several lighting installation companies around the Dallas/Fort Worth metroplex and the demand for Christmas lights increases every year. I know most of my competition in the Dallas area and, unlike other endeavors, lighting installers are courteous and helpful to each other. There is a mutual respect that exists between men and women who brave steep inclines to make their living during the holidays. I would say 80% of the companies I come into contact with know their business.

But I must issue a word of warning to the consumer- beware of the installer who offers his services for a much lower price than the competition. Exterior Christmas lights are 120 volts and therefore dangerous if not properly installed. An insufficient knowledge of electricity can lead to breakers constantly tripping or, in the worse case scenario, a fire. For your own safety research the company your are about to hire. Ask for references. Ask them how many feet of C7 lighting can be run before overloading and tripping a breaker. Ask them how long they have been in the business. Ask them if they have liability insurance.

Here are a few tips when dealing with C7 and C9 lighting:

  • C7 lights use 5 Watts of electricty (why they weren't named C5's I'll never know); C9's use 7 Watts.
  • C7 and C9 lighting are attached to 18 gauge wire; the maximum amps that 18 gauge wire can handle safely is 10.
  • The maximum number of Watts that can be run on 18 gauge wire is found using a variation of Ohm's Law.
        Power (in Watts) = Voltage (in Volts) x Maximum Current (in Amps),
        so Maximum Watts = 120 volts x 10 amps = 1200 Watts

        The maximum number of C7 bulbs that can be run
         is 1200 Watts / 5 volts = 240 bulbs x .8 resistance = 192 bulbs or 192 feet of wire
        The maximum number of C9 bulbs that can be run
         is 1200 Watts / 7 volts = 171 bulbs x .8 resistance = 136 bulbs or 136 feet of wire
  • Running more bulbs than the above figures will cause breakers to trip. If a breaker is bad, the wire will continue to heat and could catch fire.
  • If a house requires more than the maximum footage of lighting then a second timer should be installed on a separate breaker.
  • Keep in mind that adding "yard art" to the same breaker as the Christmas lights will also cause the breaker to trip if the amperage increases above safe levels. The most notorious are the blow-up Santa Clauses, etc., with an electric fan.
  • Most companies will void their warranty if the homeowner taps into their lighting system.
  • And finally, when it rains GFCI outlets can cause the breaker to trip. This does not mean you have a problem with your lights; it simply means there was sufficient moisture in the air to cause the GFCI to trip. If you are not certain where the GFCI is located, for most households it is in the garage along the common wall to the interior.