UL Information for Testing GFCI

Originally Posted By: jtedesco
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UL Information for Testing GFCI


http://www.ul.com/consumers/groundfault.html

Quote:
Product Safety Tips:
GFCIs -- A SMALL INVESTMENT, A BIG LIFESAVER
UL Recommends Regular Testing of GFCIs
December 20, 2003: Underwriters Laboratories periodically revises requirements in its Standards for Safety to harmonize with international requirements, address code and safety issues, and accommodate new product developments as applicable. UL has adopted new and revised requirements for Ground-Fault Circuit-Interrupters (GFCIs) that become effective January 1, 2003. Among others, these requirements include enhanced requirements for immunity to voltage surges, resistance to moisture and corrosion, reverse line-load mis wiring, and resistance to environmental noise. Though products meeting these revised requirements will soon enter the marketplace, they are not required to have any special markings to distinguish them from models made prior to January 1, 2003. Models of GFCIs Listed by UL that were manufactured and labeled prior to January 1, 2003 still may appear in the marketplace after January 1, 2003, and until such time as old stocks of GFCIs become exhausted.


Ground fault circuit interrupters (GFCI) can help prevent electrocution inside and outside the home. GFCIs are an effective means of protecting against electrical shock, however, they must be tested regularly -- UL recommends once a month -- to verify they are working properly.

"Ground faults" are often the result of damaged appliance cords or consumers who use electrical products in wet environments, such as bathrooms or swimming pool decks. By installing GFCIs in every home in the United States, the U.S. Product Safety Commission (CPSC) estimates that more than two-thirds of the approximately 300 electrocutions occurring each year could be prevented. The advantage of using GFCIs is that they detect even those amounts of electricity too small for your fuse or circuit breaker to activate and shut off the circuit.

Like all products, GFCIs can be damaged. GFCIs damaged by lightning or electrical surges may fail to provide adequate protection. A simple test once a month and after any violent thunderstorm should be conducted.

To properly test GFCI receptacles in your home:

Push the "Reset" button located on the GFCI receptacle, first to assure normal GFCI operation.

Plug a night light (with an "ON/OFF" switch) or other product (such as a lamp) into the GFCI receptacle and turn the product "ON."

Push the "Test" button located on the GFCI receptacle. The night light or other product should go "OFF."

Push the "Reset" button, again. The light or other product should go "ON" again.

If the light or other product remains "ON" when the "Test" button is pushed, the GFCI is not working properly or has been incorrectly installed (mis wired). If your GFCI is not working properly, call a qualified, certified electrician who can assess the situation, rewire the GFCI if necessary or replace the device.

"GFCIs are proven lifesavers, however, consumers need to take a few minutes each month to do this simple test. By taking action, you can help protect your family from the risk of electric shock," says John Drengenberg, UL Consumer Affairs Manager.

Several types of GFCIs may be installed in/around your home. Look for the UL Mark on GFCIs when purchasing them or when specifying the product to your electrician.

Wall Receptacle GFCI -- This type of GFCI -- the most widely used -- fits into a standard outlet and protects against ground faults whenever an electrical product is plugged into the outlet. Wall receptacle GFCIs are most often installed in kitchens, bath and laundry rooms, and out-of-doors where water and electricity are most likely to be in close proximity.

Circuit Breaker GFCI -- In homes equipped with circuit breakers, this type of GFCI may be installed in a panel box to give protection to selected circuits. Circuit breaker GFCIs should also be checked monthly. Keep in mind that the test will disconnect power to all lights and appliances on the circuit.

Portable GFCI -- A portable GFCI requires no special knowledge or equipment to install. One type contains the GFCI circuitry in a self-contained enclosure with plug blades in the back and receptacle slots in the front. It can then be plugged into a receptacle, and the electrical products are plugged into the GFCI. Another type of portable GFCI is an extension cord combined with a GFCI. It adds flexibility in using receptacles that are not protected by GFCIs. Portable GFCIs should only be used on a temporary basis and should be tested prior to every use.

Underwriters Laboratories Inc. (UL) is an independent, not-for-profit product safety certification organization that has been testing products for more than a century. More than 16 billion products bearing the UL Mark enter the marketplace every year.


![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: bbadger
This post was automatically imported from our archived forum.



Great Information Joe.


Originally Posted By: jtedesco
This post was automatically imported from our archived forum.



Thanks Bob:


I posted this information because there were many questions at the Lansing, Michigan NACHI Electrical Seminar yesterday, that related to the operation of the GFCI and its use in circuits with no equipment grounding conductor.

I have a few questions that were asked by the members who were present and will put them on the board when I am able.

Right now in the airport waiting for the first flight to Cincinnati and then home to Boston.

I will also look at other NEMA material I have that I will post for us to collect into our libraries. A search on the www.nema.org may also be worthwhile.

![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)

PS: Mike Holt also has an article that gives information on the subject too.


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: bbadger
This post was automatically imported from our archived forum.



It seems there is often questions about GFCIs.


I put this link up recently...

http://ecmweb.com/ar/electric_think_gfci/

...and while I think it has good information your UL info is more current. ![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif)

I wonder if there is a way to make this thread a "sticky" one? ![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif)

Bob


Originally Posted By: jtedesco
This post was automatically imported from our archived forum.



Bob:


Jack Wells is a long time electrical "roadrunner" and has been on the code panels for many years, and I would stand behind is comments.

The EC&M article you mentioned goes back to 1995, so the UL information is probably more up-to-date as.

I have some of the original articles written in the IAEI News when the GFCI was first introduced, and I also have a video that shows some of the ways in which they used humans to test them. I will try to make a few video clips that can be accessed from my website.

Although I have "sticky" function on my site I never used it and don't understand what it will do. You should make contact with the webmaster here and ask if he can accommodate your request


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: A Faxon
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icon_biggrin.gif Great info Joe. That is a very safe way to test a GFI. You diffidently will have no question of working properly or not.


Al


Originally Posted By: jtedesco
This post was automatically imported from our archived forum.



Quote:
Charles Dalziel, a professor of electrical engineering at the University of California, invented the ground-fault circuit interrupter (GFCI), in 1961.

A Look at Electrical History - A Visit with Charles Dalziel

The year is 1941. You are an assistant professor of Electrical Engineering at the University of California, Berkeley.

You are awarded a grant by the California Committee on Relation of Electricity to Agriculture.

Purpose:

To find the effects of sub lethal electrical currents on the human body. You decide to use healthy human subjects.

The subjects are given physical examinations and electrocardiograms.

Only subjects in good physical condition are used.

Subjects grasp a 12 inch length of bare copper No. 6 wire in one hand and the other hand is placed on a brass plate.

Current is passed through the person from the left hand to the right hand. The subject is asked to drop the wire.

After dropping the wire the experiment is repeated using more current, again and again, until the subject can no longer keep his hand on the eight inch diameter brass plate.

Assistants are then used to hold the subjects hand on the brass plate and the experiment continues until the subject can no longer drop the wire because he cannot let go.

http://www.joetedesco.com/gfci_history.wmv

This experiment is repeated with 28 subjects and the maximum let-go currents are tabulated and analyzed. Frequencies are changed from 60 cycles per second to 180 cps, then 500 cps, then to 1000 cps and the experiments are repeated.

It is found that the average 60 cycle let-go current for men is 16 milliamperes and the average let-go current for women is 11 milliamperes.

Your name is Charles Dalziel and you have just begun. You will establish criteria on fibrillation currents using dogs, pigs, calves, and sheep. You become the authority on dangerous electric currents.

Your experimentation will establish the principles for protecting persons from the hazards arising from the use of electricity, and your findings will be used for the notes to the Tables in Article 725 of the National Electrical Code.

http://www.electrician.com/dal.htm
? 1996 Gerald Newton. All rights reserved.



--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: jtedesco
This post was automatically imported from our archived forum.



Quote:
From the pages of Plant Engineering Magazine

Understanding GFCIs
By Mike Nager -- 4/1/2004

Advancements in electrical safety occur continuously. New products make the use of electricity safer every year. Some devices are ubiquitous but their function may not be fully appreciated. One of the most common devices in residential, commercial, and industrial safety is the ground fault circuit interrupter (GFCI).

GFCIs are well known because the National Electrical Code, NFPA 70, has mandated them in residential and commercial applications for a relatively long time. Starting in 1973, GFCI protection became a requirement for many places in the home. However, GFCIs are required for industry too. NFPA 79, the Electrical Standard for Industrial Machinery, also dictates their use in industrial applications:

"16.1.2 Receptacles, which are part of the industrial machine, either internal or external to the control cabinet and intended for use by maintenance personnel, shall have ground fault circuit interrupter (GFCI) protection for personnel."

GFCI receptacles have push buttons on the front labeled "Test" and "Reset." They protect both the outlet and the downstream circuit (Fig. 1). These buttons exercise the mechanical components of the receptacle to verify its operation. It is recommended that operation be checked monthly. Other GFCIs are built into circuit breakers and are located in panel boxes, providing both overcurrent and ground fault protection to the entire circuit.

Purpose of GFCI
The purpose of GFCIs is to prevent bodily harm from an electrical fault that causes electricity to flow through you to ground. But wait, isn't that what fuses and circuit breakers are supposed to do? Not exactly. Fuses and breakers were designed to reduce death and property damage caused by electrical fires started by short circuits and other large magnitude faults. The trouble is that the energy needed to trip a standard breaker far exceeds the lethal amount. Ground faults are most likely to occur when you are standing on ground or near a grounded piece of equipment.

How GFCIs work
GFCIs work by quickly (1/40 sec) disconnecting a current flowing through an unintended ground path (you) even if the current is too small (5 mA) to trip a normal circuit breaker (20 A). Inside a GFCI is a device that monitors the amount of current flowing through the line and compares it to the amount that returns in the neutral. If less current is present in the neutral, then a ground fault must exist somewhere in the circuit. The receptacle in turn trips (See "GFCI concepts").

At the heart of a GFCI circuit is a device that measures current in both the line and neutral. This current transformer (CT) has both the line and neutral passing through the hole and is called a differential transformer. When CTs are used for measurement you place only the line through the hole. A magnetic field is created that is proportional to the magnitude of the current passing through it. This magnetic field then creates a secondary current that is a fraction of the original, depending on its turn ratio. This transformer-type function allows you to read very high currents (for example, 100 A or even 1000 A) without having to break the conductors to install an ammeter.

As long as the same amount of current comes back on the neutral, the fields cancel out. If less current comes back, then a field is created and can be detected. This is done with a circuit that monitors the field (Fig. 2). The circuit that makes the GFCI a GFCI is a comparator. Shown in Fig. 2 as a block comprised of (and labeled as) "amplifier, comparison, and 'decision making' circuit," the comparator is what makes the decision.

The signal from the CT is amplified to a sufficient level to operate the comparator. A comparator circuit operates by comparing two inputs and reacting according to the difference it senses between its inputs. Therein lies the decision-making aspect of the circuit. The circuit is designed so that when line current and neutral current are equal, the comparator is balanced and it does not react. When a ground fault occurs, it unbalances the respective currents, raising the difference in potential applied to the comparator's inputs.

The comparator reacts by changing states. Its output is connected to a silicon controlled rectifier (SCR) trigger that disconnects the circuit. Typically the GFCI is spring-loaded, which provides the mechanical energy necessary to open the internal contacts and cut power to the circuit.

Test early; test often
GFCIs should be tested after installation and periodically thereafter, according to the manufacturer's instructions. The two buttons on the front provide an easy way to test and reset the circuit, which makes sure the spring is operating properly. Also, there are devices available for about $15 retail that will test the GFCI with a very small amount of ground fault current, ensuring that it will operate under a "real world" event. Some models indicate if the ground is connected properly or if the line and neutral are reversed.

Don't confuse GFCI with a new type of breaker called the arc fault circuit interrupter (AFCI). The purpose of the AFCI is to protect against a fire hazard that results from a low-magnitude (30 mA) short circuit between the line and neutral. Typically such a fault is caused by wire insulation damage and neither a standard circuit breaker nor a GFCI will protect against it.



Author Information
Mike Nager is the Industry Marketing Manager for Phoenix Contact Inc., Harrisburg, PA. He holds a BSEE from the University of Scranton and has 15 years experience in industrial control. Mike is Director-Elect of ISA's Food and Pharmaceutical Division. He can be reached at 800-888-7388 or mnager@phoenixcon.com.



--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm