The use of low voltage lighting systems has become increasingly popular over the past several years. Low voltage halogen and low voltage xenon lighting systems can be found in almost any setting – restaurants, hotels, bars, retail stores, museums, art galleries, offices, and the home. We have all seen these types of lighting systems in the form of cabinet lighting, cove lighting, landscape lighting, picture lights, regular track lighting, flexible track lighting (sometimes referred to as monorail lighting), cable lighting, and under cabinet lighting. Here are 15 things that you should know about these low voltage lighting systems.
Low Voltage A low voltage lighting system usually operates on 12 or 24 volts.
Transformer A transformer is generally used with low voltage lighting systems to "transform" the standard voltage that is normally available (usually 120 volts or 277 volts) to either 12 volts or 24 volts.
Type of Transformer The transformer used in a low voltage lighting system may be either electronic or magnetic.
Maximum Transformer Wattage The wattage rating of the transformer should always be equal to or greater than the total wattage of the lighting system. If an electronic transformer is used, then the maximum wattage of the lighting system may be equal to but not greater than the wattage rating of the electronic transformer. If a toroidal magnetic transformer is used, then the maximum wattage of the lighting system may be equal to but not greater than the wattage rating of the toroidal magnetic transformer. If, however, a conventional EI magnetic transformer is used, then the maximum wattage of the lighting system may be equal to but not greater than 80% of the wattage rating of the conventional EI magnetic transformer.
Minimum Transformer Wattage Transformers usually have a minimum wattage that they must power before they work. For example, it is not uncommon for 60-watt electronic transformer to require that there be at least 10 watts of lighting load and if there is only 5 watts of lighting load connected to this 60W electronic transformer, the lighting system will not work.
Electronic Transformers An electronic transformer is generally lighter in weight, smaller in size, cooler to operate, and quieter than a magnetic transformer. However, electronic transformers cannot provide more than 300 watts of power whereas some magnetic transformers can provide as much as 1200 watts of power.
Voltmeter Readings Because an electronic transformer provides its power at very high frequencies (usually greater than 20,000 Hertz) a standard voltmeter cannot be used to accurately measure the output voltage. Instead, a "true RMS" voltmeter must be used to measure the secondary voltage of an electronic transformer.
AC Electronic Transformer An AC (alternating current) electronic transformer should not be placed any farther than 10 feet from the lighting system. If it should be placed farther away than 10 feet from the lighting system, part or all of the lighting system will experience a lower voltage (known as voltage drop) and have dimmer lamps. Also, the longer the distance from the AC electronic transformer and the lighting system, the greater the chance that it might create radio frequency interference (RFI) with other electronic components in the area.
DC Electronic Transformer A DC (direct current) electronic transformer may be placed as far as 50 feet from the lighting system. The DC output significantly reduces radio frequency interference (RFI) and virtually eliminates the possibility of any voltage drop (the drop in voltage over a long circuit).
Toroidal Magnetic Transformer If a magnetic transformer is used to power a low voltage lighting system, a toroidal magnetic transformer should be considered. This type of magnetic transformer is more efficient, lighter in weight, smaller in size, cooler to operate, and quieter than a conventional EI magnetic transformer.
Wiring a Dimmer A low voltage lighting system can be dimmed whether it is powered by an electronic or a magnetic transformer. When using a dimmer with a low voltage lighting system the dimmer should always be installed so that it is controlling the line voltage side of the transformer, which is also called the primary side or the side connected to 120 volts or 277 volts.
Type of Dimmer The dimmer selected to control an electronic transformer should be specifically designed to control that type of transformer whereas a dimmer selected to control a magnetic transformer should be specifically designed to control that type of transformer.
Electrical Connections All of the electrical connections for a low voltage lighting system must be very tight and secure. If an electrical splice is not very tight and secure, the wires may arc, cause a great deal of heat, cause the entire lighting system to fail, and possibly become a fire hazard.
24-Volt Lamps When using a 24-volt transformer make certain that the lamps are rated for 24 volts - not 12 volts. If 12-volt lamps are used with a 24-volt transformer the lamps will burn out immediately and possibly become a fire hazard.
Thicker Wires Low voltage lighting systems require thicker wires (lower gauge) since more electricity is being conducted by those wires. For example, a 300-watt lighting system operating at 12 volts uses 25 amps of electricity on the low-voltage side of the transformer whereas this same transformer may be powered by 120 volts and 2.5 amps of electricity on the line voltage side of the transformer.
An abbreviated version of this article appears in the print and electronic version of the June 2008 issue of EC&M magazine. The EC&M (Electrical Construction & Maintenance) magazine is the technical authority for over 140,000 electrical professionals involved in large electrical contracting companies, industrial plants with 100+ employees, and large engineering firms. The National Electrical Code, power quality, motors and controllers, lighting, installation methods, and more are covered with in-depth articles and easy-to-understand instructions in the EC&M magazine.