Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to firstname.lastname@example.org. Answers are based on the 2014 NEC.
The fixture package on a large project includes a number of light-emitting diode (LED) fixtures with remote-controlled drivers that have to be installed in the field. The vendor informed us that the finished product was not listed. NEC 410.6 requires the fixture to be listed, not the driver. Can we use these fixtures?
No. Instead of lighting fixtures, the NEC uses the term luminaires. The answer to this question is found in Article 100 Definitions. As defined, a luminaire is a complete lighting unit consisting of a light source, such as a lamp or lamps, with the parts designed to position the light source and connect it to the power supply. The power supply is the utilization voltage, typically 120 or 277 volts (V). LED drivers are part of the luminaire. The act of changing or adding a driver or ballast to a luminaire must be done with a driver or ballast that the manufacturer identifies for that specific luminaire. Note that Section 410.6 also requires retrofit kits to be listed. The driver may be recognized for use in the luminaire. Contact the manufacturer of both the luminaire and driver to determine if they have been identified for the use. If not, you may need a research and testing company to provide an evaluation. There are many issues to consider, including, but not limited to, the amount of space inside the luminaire and the heat the driver creates.
Are transformer secondary conductors feeders?
We had a lively discussion on the job about the conductors on a transformer secondary and need clarification. The installation is a typical 150-kilovolt-ampere (kVA), 480 to 208/120V transformer. Article 100 defines feeders as the conductors between a separately derived system and the final overcurrent protective device (OCPD). If that is true, why do we have rules in Section 240.21 for transformer secondary conductors?
You are correct; the definition of feeder includes the conductors from a separately derived source (transformer, in this case) to the final OCPD. However, there is more to this story. Section 215.3 requires a feeder to have overcurrent protection in accordance with Part I of Article 240. First-level subdivision 240.4(F) provides general requirements for overcurrent protection of transformer secondary conductors. The first sentence in this requirement clarifies that all transformer secondary conductors from single-phase, 3-wire; delta three-phase, 4-wire; and wye-connected secondaries are not considered to be protected by the transformer primary OCPD. The remainder of the requirement explains how you can protect secondary conductors with the primary OCPD only for transformers that are single-phase, 2-wire to 2-wire or three-phase delta/delta, 3-wire to 3-wire. Single-phase, 3-wire and wye-connected transformer secondary conductors are not considered to be protected by the transformer primary OCPD. First-level subdivision 240.21(C) contains the requirements for overcurrent protection and installation of transformer secondary conductors. The requirements of 240.4(F) are repeated in 240.21(C)(1).
The 10- and 25-foot tap rules in 240.21(C)(1) and (C)(2) are the most common applications. Through requirements for maximum length of conductors, minimum size of conductors, installation to protect from conductors from physical damage and termination in properly sized OCPDs, an acceptable level of protection is provided for the transformer secondary conductors. An informational note with the definition of feeder in Article 100 sending the Code user to 240.21(C) for transformer secondary conductors would be extremely helpful to the Code user. (See Code in Focus, page 52, for more on taps and transformer secondary conduits.)
Outside feeder taps
I have a question about feeder tap rules where the feeder tap conductors are installed in PVC conduit under at least 2 inches of concrete. A 400-ampere (A) feeder that terminates in a wireway supplies our installation. Feeder taps from the wireway will supply four metal fabricating machines in a machine shop. The design calls for taps in the wireway with the feeder tap conductors installed in PVC under the concrete slab to the individual machines. The 400A feeder and wireway are located indoors in a mechanical room, and the machines are 50 to 100 feet away. We informed the designer that the 25-foot tap rule cannot be applied, but they claim that, since the conductors are under more than 2 inches of concrete, they are considered outside of the building; therefore, they claim, the unlimited length tap rule in Section 240.21(B)(5) can be applied. Is this permitted?
No. Section 240.21(B)(5)’s permissive requirements can only be applied where the tap conductors are located outside of a building or structure, except at the point of load termination, and comply with all of the other requirements in that section. In the installation described, the feeder tap conductors are indoors at the point of supply and the outdoor, unlimited length rule cannot be applied. Due to the distances described, the only options would be to (1) extend the 400A feeder closer to the machines and use the 10- or 25-foot tap rule or (2) apply the 10- or 25-foot tap rule at the wireway with the feeder taps terminating in fused disconnects or circuit breaker enclosures. In that case, the conductors to the individual machines would be branch circuits, not tap conductors, and could be in PVC under the concrete slab to the machines without length restriction.
Portable GFCI protection
Section 590.6(A)(1) in the NEC permits a portable ground-fault circuit interrupter (GFCI) when using permanent power in construction. We made portable GFCIs for our employees with listed products, but the inspector told us they were a violation. We used listed boxes, raised covers, GFCIs, cord connectors, cord and cord caps. What is wrong here?
The inspector is correct. A standard GFCI in a box with a raised cover and cord is not a “listed assembly” and is not intended for portable use. Only a device that is identified for “portable use” is permitted. A standard GFCI relies on 125V to the brain to sense ground-fault current and open the circuit. If the neutral in the branch circuit supplying the GFCI opens, there is a loss of power to the brain, and current will flow from the ungrounded conductor to ground without tripping. A GFCI that is “identified for portable use” will open both the grounded (neutral) and ungrounded (hot) circuit conductors upon the loss of power and will not permit current flow. This prevents current flow to ground through the GFCI under any condition and is known as open neutral protection. Listed portable GFCIs are readily available and are permitted in 590.6(A)(2) to provide GFCI protection where permanent power is used.
Is that disconnect readily accessible?
Can I mount a disconnect for a roof-mounted heating, ventilating and air conditioning (HVAC) unit inside the equipment? There are four removable panels on this unit with ample space for the disconnect to be mounted inside. Each panel has gaskets to keep water out, and each has six screws to secure the panel.
No. Mounting the disconnect behind a panel that is screwed-in-place means the disconnect is accessible but not readily accessible. However, the requirement in Section 440.14 permits the disconnect to be installed on or within the air conditioning or refrigerating equipment. Where the disconnect is mounted on the equipment, it is not permitted to be located on panels that are designed to allow access to the air conditioning or refrigerating equipment or to obscure the equipment nameplate. The requirement is for the disconnect to be “readily accessible.” The definitions for “accessible” and “readily accessible” are in Article 100. To be readily accessible, the disconnect must be capable of being reached quickly for operation, without needing to use tools, to climb over or remove obstacles, or to resort to portable ladders, and so forth. If the access door were hinged with a handle to access the disconnect, the need for tools is eliminated, and it would be considered readily accessible.