In the past few editions of the National Electrical Code (NEC), light-emitting diode (LED) illumination systems have been inserted into almost every article where lighting is mentioned. Continuing that trend in the 2011 NEC, Article 410 (luminaires) and Article 600 (electric signs and outline lighting) have been updated with additions concerning LEDs. A detailed study of LED sources is necessary to understand the benefits and the limitations of these devices.
The following information and more is available on Wikipedia: “Light--emitting diode or LED is a semiconductor light source that was introduced as a practical electronic component in 1962. Early LEDs emitted low-intensity red light, but modern versions are available across visible ultraviolet and infrared wavelengths, with very high brightness. The basic operation of an LED occurs when a light-emitting diode is forward biased (switched on); electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. LEDs are often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. On the plus side, LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. On the negative side, LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.”
Going back to the Code: Most of the requirements addressing LED luminaires in a clothes closet were accomplished in the 2008 NEC with the exception of the types of luminaires permitted in 410.16(A). The text in 410.16(A), with new text underlined, states “Only luminaires of the following types shall be permitted in a closet: (1) surface mounted or recessed incandescent or LED luminaires with completely enclosed light sources, (2) surface mounted or recessed fluorescent luminaires, and (3) surface mounted fluorescent or LED luminaires identified as suitable for installation within the closet storage space.” Section 410.16(A) provides the types of luminaires, and (C) provides the minimum clearance and specific locations for all luminaires in a closet.
LED sign illumination systems are defined as a complete lighting system for use in signs and outline lighting consisting of light-emitting diode (LED) light sources, power supplies, wire and connectors to complete the installation. In addition, a new 600.33 has been inserted into Part II of Article 600, covering secondary wiring for these LED sign illumination systems. The secondary-side wiring methods and materials of any power supplies for LED signs must be installed in accordance with the sign manufacturer’s installation instructions, using any applicable wiring methods from Chapter 3. Based on 600.12(C) with its reference to 600.33, these secondary LED power sources have an output that is Class 2 and must comply with the requirements for Class 2 circuits in Part III of Article 725. Listed Class 2 cable from Table 725.154(G) must be installed on the secondary side of the power supply, and the conductors in these cables must have an ampacity of not less than the sign load but not smaller than 22 AWG.
Where Class 2 cables supply signs in wet locations, such as LED signs mounted on the outside of a restaurant parapet, these cables must be identified for use in a wet location or have a moisture-
impervious metal sheath. In other than wet locations, LED Class 2 power sources, such as the inside of a restaurant, can be installed using any applicable Class 2 cable permitted in Table 725.154(G). This secondary Class 2 LED wiring must be installed in a neat and workmanlike manner. Where the Class 2 cables or conductors for LEDs are installed exposed on the surface of ceilings and sidewalls, it must be supported by the building structure so the cable is not damaged by normal building use. The Class 2 cable support can be straps, staples, hangers, cable ties or similar support fittings designed and installed in such a manner as to not damage the cable. For example, using nails through the cable and into drywall would not be permitted. In addition, any Class 2 wiring method for LED sign wiring must be protected within a wall or ceiling in accordance with 300.4. Unlike most Class 2 systems, Class 2 LED wiring must comply with 600.7 for equipment grounding and bonding.
As more incandescent lamps and luminaires are phased out in favor of these more efficient light sources, there will be additional changes in the future, so watch the proposals and comments for the 2014 NEC process.
For more on LEDs, check out the special report—The LED Revolution—that appeared in the July 2011 issue of ELECTRICAL CONTRACTOR.
ODE is a staff engineering associate at Underwriters Laboratories Inc., based in Peoria, Ariz. He can be reached at 919.949.2576 and firstname.lastname@example.org.