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


<< First < Previous 1 2 3 Next > Last >>

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.
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
IIoT grows up; Six ways to lower IIoT costs; Six mobile safety strategies; 2017 Salary Survey
2016 Top Plant; 2016 Best Practices on manufacturing progress, efficiency, safety
2016 Product of the Year; Diagnose bearing failures; Asset performance management; Testing dust collector performance measures
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Big Data and bigger solutions; Tablet technologies; SCADA developments
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
What controller fits your application; Permanent magnet motors; Chemical manufacturer tames alarm management; Taking steps in a new direction
Tying a microgrid to the smart grid; Paralleling generator systems; Previewing NEC 2017 changes
Package boilers; Natural gas infrared heating; Thermal treasure; Standby generation; Natural gas supports green efforts

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on the vital role of plant safety and offers advice on best practices.
This article collection contains several articles on preventing compressed air leaks and centrifugal air compressor basics and best practices for the "fifth utility" in manufacturing plants.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
click me