NEC Chapter 2: Wiring and protection

08/14/2013


Terminal identification

Figure 5: Old non-grounding receptacles with grounded terminals are identified by white screws and a plate. Age: 50-plus years. These were phased out after the 1962 NEC required grounding receptacles. Courtesy: CH2M HillFor devices 30 amp and less, terminals must be identified. Ungrounded terminals must be distinguishable from the grounded terminals. Receptacles, plugs, and connectors require white metal or a “W” or “white” label. If the terminal is not visible, as in the case of push-pin devices, the label is required. Identification of terminals for devices has been in practice for a long time. Even this old two-pin device has white terminals for the grounded connection. 

Where leads are provided with a screw shell, they must have a white or gray colored jacket for the conductor attached to the screw shell. Appliance termination requirements have a separate point. Appliances with line-to-ground connections either hardwired or cord and cap require the grounded terminal to be identified. 

Looking forward to the 2014 Edition of the NEC, one option to be voted on is whether gray stripes are an acceptable means of identification. For seven points where white stripes are allowed, gray stripes have been proposed as an option. Point 200.2 revisions have been proposed by a high-voltage task group looking to improve consistency when discussing 1000 V system divisions. Another proposal was to add a “fine print note” to 200.1 Scope with reference to 250.26 for when a grounded conductor is a neutral conductor. However, this proposal was rejected because, according to the code-making panel, “whether a grounded conductor is a neutral or not is not relevant to the requirements of Article 200.” 

Identification of the grounded conductor is straightforward once you have taken the time to understand Article 200. Mistakes not only cause confusion during commissioning, but also can be deadly. 


John Schuring is an electrical engineer at CH2M Hill with more than 20 years of engineering experience. He works primarily in industrial applications and start-up of facilities.


Definitions

Several important definitions from NEC Article 100 are: 

Grounded conductor. A system or circuit conductor that is intentionally grounded.

Grounding conductor, equipment (EGC). The conductive path(s) installed to connect normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.

Neutral conductor. The conductor connected to the neutral point of a system that is intended to carry current under normal conditions. 

Neutral point. The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system. Informational note: At the neutral point of the system, the vectorial sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutral point, is zero potential


References

IEEE Std 142-2007

National Electric Code Handbook, 2011

NFPA 70: Report on Comments-June 2013

NFPA 70: 2014 Report on Proposals


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Pete , United States, 08/21/13 12:12 PM:

Great Article, I've tried to explain same, hundreds of times, this distills it very well.
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