Fixture Whip Wiring Methods for Class 2 LED Drivers – Frequently Asked Questions
posted Wednesday Aug 07, 2019 by TURTLE & HUGHES in Products and Technology
This week, we are pleased to present a guest blog courtesy of our supplier partner, AFC Cable Systems, a Part of ATKORE International.
Are LED Driver Output Circuits Class 1 or Class 2 Systems?
Lighting systems operating at 30-volts or less shall be listed as a complete system per National Electric Code (NEC) section 411.3, however individual LED drivers that are identified as recognized components by a Nationally Recognized Testing Laboratory (NRTL) are also permitted when part of a listed system.
The drivers used in a typical LED lighting system in residential and commercial applications are listed as Class 2 or are individually identified as recognized components and intended to be used as part of an NRTL listed field-installed LED lighting assembly.
Class 2 LED drivers that are listed or part of a listed system comply with UL 1310 Standard for Safety for Class 2 Power Units which requires the output voltage to pose no risk of fire or electric shock which makes secondary circuit protection unnecessary.
The UL standard restricts the driver output to less than 60 volts in dry applications and less than 30 volts in wet applications. To be listed, the secondary current cannot exceed 5 amps and the total power output rating must be less than 100 watts.
The standard also requires Class 2 LED driver to be clearly identified as a Class 2 Power Supply.
Although they are low-voltage, LED drivers that are not marked as Class 2 have a voltage output above the limits of UL1310 and are considered Class 1. The power output of the secondary of an LED driver with a Class 1 rating is over the maximum 100 watts.
Note that the terms "low voltage" or "limited energy" may be used by manufacturers but only a listed or recognized component Class 2 power supply qualifies for the less restrictive NEC installation conditions.
Can the control conductors for LED Drivers with 0-10 volt dimming systems be installed in the same raceway as the supply (power) conductors?
YES. Installers can be confused by the permission found in NEC section 300.3(C) allowing conductors to occupy the same enclosure, cable, or raceway when all conductors have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within that enclosure, cable, or raceway.
This allowance does not apply when the LED driver is identified as a Class 2 device. The Informational Note following section 300.3(C) directs the user to NEC Article 725 Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits.
Section 725.136 requires Class 2 conductors be isolated from power conductors.
The possibility that a Class 2 conductor could come in contact with and become energized at a higher voltage is the reason that it not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power or Class 1 circuits.
How can a raceway (Fixture Whip) with listed LED power and control wiring comply with the separation requirement?
As with most hard-and-fast code rules, there are exceptions and allowances. NEC Section 725.136(I) allows Class 2 conductors to be installed with conductors of electric light, power, and Class 1 circuits when a minimum 2-inches of separation is maintained or if all of the Class 2 circuit conductors are in non–metallic-sheathed cables in addition to the insulation on the conductors.
In compliance with the rules in 725.136(I)(1) a Fixture Whip must be specifically designed for LED power and control wiring. In addition to the use of a listed Flexible Conduit, the Insulated power conductors must be a 600-volt wire Type, and the 0-10-volt control conductors must be contained in a listed 600-volt non-metallic cable type covered in Chapter 3 of the NEC. The use of No. 16 or 18 AWG sized conductors for the 0-10-volt control conductors limits the non-metallic cable type to Power and Control Tray Cable: Type TC covered in Article 336.
The Type TC Cable containing the Class 2 circuit conductors creates and maintains the code-required barrier allowing the Class 2 and power conductors to be in the same raceway without risk of possible contact.
How can the Fixture Whip be used and still maintain the required separation in enclosures?
Answer: NEC 725.136(D) applies to the installation of associated systems and allows Class 2 circuit conductors in compartments, enclosures, device boxes, outlet boxes, or similar fittings with the power conductors when they to connect to the associated equipment and are routed so that at least a ¼-inch space is maintained between the Class 2 and power conductors.
When terminating this the conductors of the Fixture Whip the power conductors and the Class 2 conductors within the Type TC cable enter the enclosure as one assembly, but installers must take care not to remove the jacket from the TC cable. Remembering that the Class 2 and power conductors are generally required to be individually separated, TC jacket material should remain intact as close as practicable to the terminal.
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