Jan
21

Misunderstood After All This Time: Isolated Grounding

By Mark C. Ode, lead engineering associate for Energy & Power Technologies 

I recently received an email from a homeowner who was installing a high-end media room and had questions about his home's electrical system and the new circuits for the audio/video equipment. Before doing the installation, the homeowner had conducted internet research on the background requirements for audio/video installations. He also contacted an electrician friend, the audio/video equipment manufacturer from whom he had purchased his equipment, and an audio company engineer.

The audio equipment manufacturer provided a 65-page instruction manual with diagrams and illustrations to help with equipment installation. In addition, the electrician friend and the audio company engineer provided conflicting information and the homeowner was having trouble understanding the manual.

He found an article I had written for ELECTRICAL CONTRACTOR on isolated ground receptacles and circuits, so he contacted me to see if I could clarify the project and get him on the right path.

In the end, he relied upon the information I gave him, along with his electrician, to perform a safe installation.

According to my interpretation of his email, the homeowner had a service panelboard on the outside of the house and wanted to install a six-circuit panel in his media room with four dedicated 20-ampere (A), 120-volt (V) circuits to supply the audio/video equipment. He wanted to install EMT from his service panel to the media room panel and to four separate metal boxes in the room with a single 20A, 120V dedicated circuit in each box. He also wanted a separate isolated and insulated equipment grounding conductor for each circuit. At the media room panel, he wanted a separate isolated equipment ground bar for the four isolated, insulated equipment grounding conductors.

He was confused about what was permitted and what was required.

The audio company engineer told him to install a "2/0 welding cable from the isolated equipment ground bar in the media room panel to two separated ground bars" located outside of the building. (I assume the engineer meant two ground rods.) This concept was proposed in the 1980s to help isolate computers, audio and video equipment, and other high-frequency sensitive equipment from the normal electrical grounding system. However, this installation would have created an isolated ground without a path for fault current back to the source and would not have adequately cleared a fault in one of the circuits by tripping a breaker or blowing a fuse.

This incorrect concept prompted an addition to the 1990 National Electrical Code (NEC) in 250-21(d) (covering objectionable current over grounding conductors), which states: "the provisions of this section shall not be considered as permitting electronic equipment being operated on AC systems or branch circuits that are not grounded as required by this Article. Currents that introduce noise or data errors in electronic equipment shall not be considered the objectionable currents addressed in this section."

In other words, totally isolating the equipment grounding conductors from the electrical system using two separate ground rods was not acceptable in 1990, and it is not acceptable now. Thankfully, I quickly cleared up that misconception for the homeowner.

High-frequency noise, other unwanted frequencies and signals, harmonics, and even a signal that originates within the electronic equipment itself may be capacitive and inductively coupled into the ferrous metal raceway, connecting the equipment and the panel, and can be reflected back into the equipment, causing major disruption and noise in the audio and video equipment. There are two sections in the NEC that will help someone trying to reduce electrical noise (electromagnetic interference) on the grounding system. Isolated grounding of permanently installed electronic equipment is dealt with in 250.96(B) and 250.146(D) with isolated grounding of cord-and-plug-connected electronic equipment.

In both cases, a separate insulated, isolated equipment-grounding conductor can be installed from the equipment (a nonmetallic bushing isolates the metal raceway from the metal frame of the electronic equipment) or from the isolated ground receptacle (the ground pin of the receptacle is not connected to the yoke of the receptacle) back to the main service or the source of the separately derived system without being connected to metal boxes or subpanels. This separation and isolation keeps unwanted noise and other frequencies from being coupled into the electronic equipment and still provides a path for fault current back to the source.

Metal boxes, metal subpanels, metal raceways and other metal enclosures from the permanent electronic equipment or isolated ground receptacles still are required to have normal equipment grounding. 

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See the original full article at: https://www.ecmag.com/section/codes-standards/misunderstood-after-all-time-isolated-grounding

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Jan
10

IEEE Publishes a Guide for Arc-Flash Hazard Calculations

 This guide provides mathematical models for designers and facility operators to apply in determining the arc-flash hazard distance and the incident energy to which workers could be exposed during their work on or near electrical equipment.

The IEEE Standards Association, Piscataway, N.J., has published a new guide for understanding and calculating arc-flash hazards in electrical equipment. The new IEEE 1584-2018—IEEE Guide for Performing Arc-Flash Hazard Calculations was produced in collaboration with the National Fire Protection Association (NFPA) as part of an effort to provide the industry with improved models and an analytical process to enable calculation of predicted incident thermal energy and the arc-flash boundary, IEEE said in a release announcing the guide's publication.

Sponsored by the IEEE Industry Applications Society, Petroleum & Chemical Industry (IAS/PCIC), this new technical standard is the result of extensive research and laboratory testing conducted by the Arc Flash Research Project.

"Our extensive, collaborative work with the NFPA has resulted in an IEEE standard that dramatically improves the prediction of hazards associated with arcing faults and accompanying arc blasts," said Konstantinos Karachalios, managing director of the IEEE Standards Association. "Contractors and facility owners will benefit from IEEE 1584 by being able to more thoroughly analyze power systems to calculate the incident energy to which employees could be exposed during operations and maintenance work, allowing them to provide appropriate protection for employees in accordance with the requirements of applicable electrical workplace safety standards."

IEEE 1584-2018 includes processes that cover the collection of field data, consideration of power system operating scenarios, and calculation parameters. Applications include electrical equipment and conductors for three-phase alternating current voltages from 208 V to 15 kV.

"The update to IEEE 1584 has empowered thousands of engineers conducting Arc-Flash Hazard Calculations," said Daleep Mohla, chair, IEEE 1584 Arc-Flash Hazard Calculations Working Group. "These efforts, conducted in partnership with the NFPA, have armed all stakeholders involved in Arc-Flash hazards to better protect employees and contractors in the working environment."

More information on IEEE 1584-2018 is available here.

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Jan
07

The Seven Types of Power Problems

Many of the mysteries of equipment failure, down-time, software and data corruption, are the result of a problematic supply of power. There is also a common problem with describing power problems in a standard way. This white paper describes the most common types of power disturbances, what can cause them, what they can do to your critical equipment, and how to safeguard your equipment, using the IEEE standards for describing power quality problems.

Our technological world has become deeply dependent upon the continuous availability of electrical power. In most countries, commercial power is made available via nationwide grids, interconnecting numerous generating stations to the loads. The grid must supply basic national needs of residential, lighting, heating, refrigeration, air conditioning, and transportation as well as critical supply to governmental, industrial, financial, commercial, medical and communications communities. Commercial power literally enables today's modern world to function at its busy pace. Sophisticated technology has reached deeply into our homes and careers, and with the advent of e-commerce is continually changing the way we interact with the rest of the world.

Many power problems originate in the commercial power grid, which, with its thousands of miles of transmission lines, is subject to weather conditions such as hurricanes, lightning storms, snow, ice, and flooding along with equipment failure, traffic accidents and major switching operations. Also, power problems affecting today's technological equipment are often generated locally within a facility from any number of situations, such as local construction, heavy startup loads, faulty distribution components, and even typical background electrical noise.

Widespread use of electronics in everything from home electronics to the control of massive and costly industrial processes has raised the awareness of power quality. Power quality, or more specifically, a power quality disturbance, is generally defined as any change in power (voltage, current, or frequency) that interferes with the normal operation of electrical equipment.

The study of power quality, and ways to control it, is a concern for electric utilities, large industrial companies, businesses, and even home users. The study has intensified as equipment has become increasingly sensitive to even minute changes in the power supply voltage, current, and frequency. Unfortunately, different terminology has been used to describe many of the existing power disturbances, which creates confusion and makes it more difficult to effectively discuss, study, and make changes to today's power quality problems. The Institute of Electrical and Electronics Engineers (IEEE) has attempted to address this problem by developing a standard that includes definitions of power disturbances. The standard (IEEE Standard 1159-1995, "IEEE Recommended Practice for Monitoring Electrical Power Quality") describes many power quality problems, of which this paper will discuss the most common.

​Seven Types of Power Problems Summarized

For more information on this topic, please download White Paper 18, The Seven Types of Power Problems.

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See the original full article at: https://www.apc.com/us/en/support/resources-tools/white-papers/the-seven-types-of-power-problems.jsp

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Dec
31

We can all do more to advance NEC 210.8

Our industry has made numerous technological advances designed to protect homeowners, businesses and electrical workers. That makes every fatal electrocution in the home all the more distressing. Between 2010 and 2013, the U.S. saw an estimated average of 48 electrocution fatalities associated with consumer products per year, with large and small electric appliances chief among them1. Tragedies like these can be avoided, especially when the ground fault circuit interrupter (GFCI) technologies needed to prevent dangerous events are readily available.

As the principle NEMA representative at the National Electrical Code (NEC) Code-Making Panel Two, I saw public input asking for increased GFCI protection for the home during the 2017 code cycle. The code panel expanded the GFCI requirement for facilities other than dwelling units as part of section NEC 210.8(B). However, residential standards improvements were sidelined.


GFCI challenges and misconceptions

The rationale behind forgoing residential standards improvements was cost and convenience. One could argue, for example, that if GFCI requirements in a kitchen were to expand beyond sink and water areas and be specified for an appliance like a refrigerator, a potential nuisance trip could result in mass amounts of spoiled food. This inconvenience translates into real dollars for homeowners. Another barrier to code change is cost impacts for builders as increasing the number of GFCIs in a home raises electrical infrastructure expenses that must then be passed on to homebuyers.

As both an industry expert and a homeowner, I completely understand code update consequences. The change could likely put builders in an uncomfortable position of explaining why their costs have gone up seemingly overnight. Speaking as a VP of sales, justifying a price increase is always a challenge, and I take great pains to make sure my customers understand how the technology is worth the investment and can result in safer environments. The reality is that a residential requirement won't put much of a financial burden on contractors and homeowners. For instance, expanding GFCI requirements throughout a home in the $200k price range would increase the cost of a 30-year mortgage by mere pennies a month. By highlighting the features and benefits of GFCIs, homeowners are more likely to accept minimally higher costs to protect their loved ones.

Nuisance tripping is a valid concern from a convenience perspective. For the most part, however, the greater majority of unwarranted trips are behind us. When GFCIs first hit the market in the early 1970's, appliances inherently had leakage currents that flowed over the equipment grounding conductors, causing false trips. The development of appliances and their standards have come a long way as standards now place a cap on how much leakage current any single appliance is permitted to have. It would be bullish to say homeowners will never experience a false trip with a GFCI, especially if there's an un-listed product that generates nuisance currents on the circuit. But when we compare the small number of nuisance trips against markedly increased safety, there's simply no way to justify leaving the residential code as is.


Installing more residential GFCIs can help the industry

I understand how the wheels of progress spin; affecting change takes time. While I'm hopeful we can collectively approve GFCI changes for the whole home, realistically I'd be pleased with any positive strides. Something as simple as including 30-amp GFCI receptacles on clothes dryer circuits, for instance, would greatly enhance safety since dryers are often within proximity of a water source. If we demonstrate to homeowners how installing the additional GFCI on this circuit makes for a safer home, the hope is the industry will acclimate to slight cost increases and, over time, routinely install GFCIs throughout entire households.

The challenge ahead of us is to generate more dialogue during the 2020 code-review cycle, and we need new data to spawn conversation. Collecting data starts with one small step, one change in the way we do business. I ask that we as an industry consider going above and beyond NEC 210.8 guidelines and install additional GFCI protection in homes to increase safety and acquire the information needed to make change possible. 


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See the original full article at: http://www.eaton.com/us/en-us/company/news-insights/for-safetys-sake-blog/advance-nec.html

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Dec
17

9 ways beer and UPSs are alike

Here is a little fun before the holidays, by Eaton: 

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See the original full article at: https://switchon.eaton.com/plug/journey/business-continuity/infographic/9-ways-beer-and-UPSs-are-alike-infographic

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