History of GFCIs

History of GFCIs

Charles Dalziel

Charles Dalziel (1904-1986), a professor of electrical engineering at the University of California, invented the ground-fault circuit interrupter (GFCI) in 1961. He came to realize that a common cause of deaths was the result of ordinary household circuits malfunctioning in the ground fault. His research objective then became to create a device which would interrupt a ground-fault current before it became large enough to cause human physiological damage. The sensitivity, speed of action, reliability, small size, and cost required made the device almost impossible to design.

However, in 1965, Dalziel received a patent for a “ground-fault current interrupter” that would interrupt current before it grew to 0.005 of an ampere, and which was small, reliable and inexpensive. The device was based on a magnetic circuit plus a then newly developed semiconductor device.

Most of the time, his invention does nothing; it just monitors the difference in the current flowing into and out of a tool or appliance. But when that difference exceeds 5 milliamps (nominal), an indication that a ground fault may be occurring, the GFCI shuts off the flow in an instant — in as little as 0.025 of a second.

How does a GFCI work?

GFCIs are designed to sense any difference in current between the supply on the ungrounded (hot) conductor in a circuit, and the grounded (neutral) conductor.

If the circuitry recognizes a differential of more than 5 milliamps (nominal) between supply and return, a solenoid trips open the circuit, causing all power to be disconnected.

For this reason, a GFCI breaker, or a correctly wired GFCI receptacle, can protect all outlets farther downstream.

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Types of GFCI Devices

There are four basic types of GFCI in common usage, and two or three of them are common in residential construction. They are:

  1. 1)  GFCI breakers in the distribution panel;

  2. 2)  GFCI receptacles at in-home locations;

  3. 3)  Stand-alone GFCIs, as sometimes used with pools; and

  4. 4)  Extension cords with built-in protection, primarily found on construction sites.


GFCI on 2-Wire Circuits

 
There is a common misconception that GFCIs work only on grounded circuits. This is not entirely the case. While there are conditions under which the GFCI will not be able to trip without a ground, the inspector should still recommend that any circuits in potentially wet or damp locations be fitted with them as a safety precaution.

GFCI Requirements

Bathroom

To protect people, ground-fault circuit interrupter (GFCI) protection should be installed in all bathrooms with 125-volt, single-phase, 15- and 20-ampere receptacles.


Laundry

To protect people, ground-fault circuit interrupter (GFCI) protection should be installed in laundry rooms with 125-volt, single-phase, 15- and 20-ampere receptacles.

 

Garage and Accessory Buildings

To protect people, GFCI protection should be installed at all 125-volt, single-phase, 15- or 20-ampere receptacles installed in garages and grade-level portions of unfinished accessory buildings used for storage or work areas.

Outdoor

To protect people, GFCI protection should be installed at all 125-volt, single-phase, 15- and 20-ampere receptacles installed outdoors, except for receptacles not readily accessible that are used for temporary snow-melting equipment and are on a dedicated circuit.

Crawlspace

To protect people, GFCI protection should be stalled at all 125-volt, single-phase, 15- and 20-ampere receptacles in the crawlspace when such place is at or below grade level.

Unfinished Basement

To protect people, GFCI protection should be installed at all 125-volt, single-phase, 15- and 20-ampere receptacles installed in unfinished basements. Unfinished basements are defined as portions or areas of the basement not intended as habitable rooms such as storage and work areas. The exception would be a receptacle supplying only a permanently installed fire alarm or burglar alarm system.

Kitchen

To protect people, GFCI protection should be installed at all 125-volt, single-phase, 15- and 20-ampere receptacles that serve countertop surfaces.


Sink

To protect people, GFCI protection should be installed at all 125-volt, single-phase, 15- and 20-ampere receptacles that are located within 6 feet of the outside edge of a sink, bathtub or shower. Receptacle outlets shall not be installed in a face-up position in the counter top or work surface.

Boathouse

To protect people, GFCI protection should be installed at all 125-volt, single-phase, 15- or 20-ampere receptacles installed in boathouses.

Boat Hoist

To protect people, GFCI protection should be installed for outlets supplying up to 240 volts at boat hoists.

Electrically Heated Floors

To protect people, GFCI protection should be installed at electrically heated floors in bathrooms, kitchens and in hydro-massage bathtub, spa and hot tub locations.

GFCI Locations

GFCIs should be installed in readily accessible locations. 

GFCI protection is recommended for the following:

  • 15- and 20-amp kitchen countertop receptacles and outlets for dishwashers
  • 15- and 20-amp bathroom and laundry receptacles
  • 15- and 20-amp receptacles within 6 feet of the outside edge of a sink, bathtub or shower
  • Electrically-heated floors in bathrooms, kitchens, and hydromassage tubs, spas, and hot tubs
  • 15- and 20-amp exterior receptacles, which must have GFCI protection, except for receptacles not readily accessible that are used for temporary snow-melting equipment and are on a dedicated circuit
  • 15- and 20-amp receptacles in garages and unfinished storage buildings
  • 15- and 20-amp receptacles in boathouses and 240-volt and less outlets at boat hoists
  • 15- and 20-amp receptacles in unfinished basements, except receptacles for fire or burglar alarms
  • 15- and 20-amp receptacles in crawlspaces at or below ground level
  • 15- and 20-amp receptacles in indoor damp and wet locations

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Since the early 1970s, GFCIs have been required in an increasing number of damp and wet locations, and, more recently, this requirement has extended to all receptacles in garages. Because they are safety devices, the home inspector should check every installed GFCI circuit and may advise the client of areas where they should also be fitted.
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