Arc flash relays meet code compliance

Revised NEC 240.87 requirements make mitigation easier to achieve.

06/04/2015


Arc flash relays use either point or fiber-optic light sensors to detect an arc and send a trip signal to the circuit breaker in <1 ms. Courtesy: Littelfuse

Besides wanting to comply with state regulations, managers knew that insurance providers expect equipment to meet minimum design standards, which the NEC provides. They discovered that the code change makes it easier to protect workers and equipment from arc flash hazards.

In 2014, the NEC was revised in multiple areas. Changes to Paragraph 240.87 have made compliance simpler and less expensive. One easy-to-apply device can simplify meeting the new requirements while providing important additional safeguards for people and equipment.

The previous version of the Code

Paragraph 240.87 of the 2011 edition of the NEC, which was titled Non-instantaneous Trip, said that whenever using a circuit breakerwith a rating of 1,200 A or higher (or one that could be adjusted to 1,200 A or higher) that did not have an instantaneous trip function, one of the following was required:

  1. Zone-selective interlocking
  2. Differential relaying
  3. An energy-reducing maintenance switch with local status indicator.

Zone-selective interlocking addresses a shortcoming of selective coordination. It involves interconnecting downstream and upstream circuit breakers: If a short circuit or ground fault occurs on a branch circuit, the breaker feeding it will trip instantaneously, and simultaneously send a signal to the breaker just upstream, telling it to use its time-delay function instead of tripping instantaneously.

This is important because, otherwise, a downstream short or ground fault could draw enough current to cause both breakers to trip instantaneously, killing power to branch circuits other than the one with the fault.

An unfortunate drawback is that an arc flash may not immediately draw enough current to trip either breaker, resulting in personal injury and damage or destruction of equipment.

Differential relaying uses current transformers at the inputs and outputs of the electrical equipment being protected (zones). When a fault occurs, the zone in which the input and output currents do not match is the location of the fault, and the appropriate breaker is tripped. This is complicated and expensive and takes up a fair amount of space.

An energy-reducing maintenance switch manually sets the current pickup lower and the time delay faster, to trip the breaker feeding a panel as fast as possible while someone is working on it. If there is an arc flash, the breaker should trip instantaneously and limit the energy delivered. This reduces the level of PPE required for the panel. The switch must be activated manually before beginning the maintenance activity to provide protection, and deactivated afterward to prevent future nuisance tripping or miscoordination.

The current version of the Code

The 2014 edition of the NEC changed the name of paragraph 240.87 to Arc Energy Reduction and focused more on personnel protection. As explained in the “2014 NEC Handbook,” the change to this section removes the mention of instantaneous tripsetting from the criteria for applying this requirement. 

Instead, it is now required where the highest continuous current trip setting in a circuit breaker is rated or can be adjusted to 1,200 A or higher. It allows for two new methods that can make the job of compliance a good deal easier:

  • An energy-reducing active arc flash mitigation system
  • An approved equivalent means.

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

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.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
A new approach to the Skills Gap; Community colleges may hold the key for manufacturing; 2017 Engineering Leaders Under 40
Doubling down on digital manufacturing; Data driving predictive maintenance; Electric motors and generators; Rewarding operational improvement
2017 Lubrication Guide; Software tools; Microgrids and energy strategies; Use robots effectively
The cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Power system design for high-performance buildings; mitigating arc flash hazards
Research team developing Tesla coil designs; Implementing wireless process sensing
Commissioning electrical systems; Designing emergency and standby generator systems; Paralleling switchgear generator systems

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.
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me