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A Well Lit Garden

The fine art of Landscape Lighting

My low voltage garden lighting transformer is rated for 150 Watts. What will happen if I put 160 Watts on the line?

Low voltage Outdoor Lighting is defined by the National Electrical Code (NEC) as operating at or below 30 volts AC. Typically these systems use a magnetic transformer to step down your household voltage from 120 volts AC to 12 volts AC. When calculating the load on a transformer (for outdoor lighting) you must take into consideration the voltage drop that occurs on the wire. This voltage drop is SIGNIFICANT in low voltage landscpe lighting systems. Indoor systems (120 volts AC) do not have much voltage drop, therefore, do not present the same risk as an outdoor low voltage system. The NEC recommends that you de-load a low voltage system to accommodate for voltage drop on the wire. As a general rule de-load the transformer's maximum rated load by 20%. This means that the sum of your light fixtures must not exceed 80% of the manufacturer's maximum transformer rating. A 150 Watt transformer should only be used in support of 120 Watts (150 Watts * 80% = 120 Watts) of load. If you are using 10 Watt light bulbs in each fixture, then you should not connect more than 12 fixtures per transformer. The consequences of exceeding the manufacturer's maximum transformer wattage are excessive heat in the transformer's coils and reduced voltage output. Long term overloading can result in the possible failure of the transformer and is a fire safety risk. Please, be careful in setting up any outdoor garden lighting system. Seek qualified advice and contact a qualified contractor if you do not feel confident in dealing with these types of issues. Good luck and enjoy the night.