In The Drink

In the 2011 and previous editions of the National Electrical Code (NEC), installing low-voltage lighting in close proximity to the edge of a swimming pool was a Code violation, yet almost every backyard swimming pool with a landscaped yard has low-voltage lighting too close to the pool’s edge. Low-voltage lighting systems are not permitted to be installed within 10 feet of the nearest edge of the water for a pool, spa or fountain, unless otherwise permitted by Article 680. With the acceptance of new text in 680.22(B)(6) of the 2014 NEC, many of these installations will now be compliant. Let’s first look at the previous requirements for these applications and then explore the new wording that will permit low-voltage lighting in close proximity to a pool with the technical explanation for this new permission.

A low-voltage landscape lighting system primarily includes a power supply, a flexible cord to supply power to the luminaires, wire and device connectors, and any associated components necessary for completion of the system. The Standard for Low-Voltage Landscape Lighting Systems, UL 1838, covers the safety and listing requirements for landscape lighting systems, while the NEC covers the safe installation of these systems. The power supply for landscape lighting can be a cord-and-plug connection to an outdoor receptacle or a permanent connection to conduit, direct burial UF cable, or other NEC Chapter 3 wiring methods, depending on the specific product standard and compliance with Article 411. Section 411.3(A) requires a listed low-voltage system or 411.3(B) requires all of the parts to be listed.

Since low-voltage lighting systems are required to be listed, NEC 110.3(B) mandates the listing and labeling instructions and the markings, ratings and installation instructions be followed. The ratings and markings on the power supply, as well as the installation instructions, will limit the number of individual low-voltage branches or circuits that the power supply can serve.

Any number of individual branches can be supplied from the power supply or transformer, depending on the system’s design, but the total wattage of the luminaires on all the branches cannot exceed the rating of the transformer or power supply. The power supply rating will determine the overall number and wattage of the luminaires that can be supplied from each branch of the power supply. NEC 411.2 provides the definition for low-voltage lighting systems and states that one or more power supply secondary low-voltage circuits are permissible, but each circuit is limited to 25 amperes (A) maximum with a maximum voltage of 30 volts (V), alternating current (AC) or direct current (DC). Low-voltage lighting systems can have a maximum voltage of 30V AC or DC with a peak voltage that cannot exceed 42.4V under any load conditions. The 30V in the definition in 411.2 is an rms value that can be exceeded only by an instantaneous peak of 42.40V.

Even though Tables 11(A) and (B) in Chapter 9 apply to Class 2 and Class 3 power supplies and are not specific to low-voltage lighting systems, these tables can provide information for acceptable AC and DC voltage for both dry and wet locations. A nonsinusoidal peak voltage of 42.4V for an AC circuit is considered a safe voltage under dry conditions and would not normally constitute a shock or fire hazard. In wet conditions, this voltage is limited to 15V for a sinusoidal AC and 21.2V peak for a nonsinusoidal. Since water decreases the body’s resistance, the permissible voltage of the low-voltage system’s output is decreased to ensure safe handling and operation of these circuits where water is a concern. Using low-voltage systems in proximity to swimming pools should only be considered when all the NEC requirements are applied.

For DC circuits, there are two conditions possible: a pulsating DC or a nonpulsating DC circuit. With pulsating DC, where the rate is 10 to 200 hertz, the maximum safe voltage in a dry location is considered to be 24.8V peak. Pulsating DC at these low frequencies can have an effect on the human body by disrupting the electrical signals to muscles and other organs.

The proposed new 680.22(B)(6) states: “Low-Voltage Luminaires. Listed low-voltage luminaires not requiring grounding, not exceeding the low-­voltage contact limit, and supplied by listed transformers or power supplies that comply with 680.23(A)(2) are permitted to be located less than 1.5 m (5 ft) from the inside walls of the pool.” Section 680.23(A)(2) states that transformers used for low-voltage lighting around pools shall incorporate isolated windings with an ungrounded secondary and a grounded metal barrier between the primary or secondary or double insulation between the primary and secondary windings. This change should provide safety for low-voltage lighting systems close to pool or spa edges.

About the Author

Mark C. Ode

Fire/Life Safety Columnist and Code Contributor
Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and .

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