Ground Fault Interrupters

Where are GFCIs required?

GFCIs (Ground Fault Circuit Interrupters) are required in many locations, particularly where water and electricity may meet. The NEC (National Electrical Code) requires GFCIs in kitchens, bathrooms, garages and outdoor locations.

Can I use a GFCI in a 2 wire (ungrounded) circuit?

Yes. A GFCI monitors for a current imbalance between the hot and the neutral conductors therefore a ground connection is not necessary. This is allowed per article 210-7 of the National Electric Code.

receptacles break only the hot wire when they trip?

No, all of our GFCI products break both line and neutral when tripped.

More information about GFCI

The following article from sci.engr.electrical.compliance newsgroup is published in this web site with permission form Rich Nute.

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From: [email protected] (Rich Nute)
Newsgroups: sci.engr.electrical.cmpliance
Subject: Re: Ground Fault Interrupters - Internationally
Date: 18 Dec 1996 20:47:20 GMT
Organization: Hewlett-Packard, San Diego Division
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Hello from San Diego:

GFCI (aka GFI)  =  Ground Fault Circuit Interrupter  (USA, Canada)
ELCB (aka ELB)  =  Earth Leakage Circuit Breaker     (U.K.)
RCCB (aka RCB)  =  Residual Current Circuit Breaker  (Europe)

All of these devices operate on the same principle.

The live and neutral wires are passed through a magnetic core. Under normal conditions, because the current in both conductors is equal and opposite, there is no flux in the core.

Under certain fault conditions, the current in the live wire can exceed the current in the neutral wire. This produces flux in the core.

In the GFCI, the core has a secondary winding. When there is flux in the core, the secondary winding produces a voltage. The voltage is applied to a solid-state amplifier whose output is applied to a relay coil. The relay interrupts the line and neutral conductors.

Typical GFCI is built into a 120-volt duplex outlet. It trips at 5 mA.

Other GFCIs are built into 15-amp circuit breakers. These trip at 20 mA to account for the leakage of the wiring between the panel board and the devices being protected.

GFCIs almost always include a test button and a reset button.

In ELCBs and RCCBs, the core is part of a relay. The magnetic flux is coupled directly to the relay, which opens the circuit. Because these devices are totally magnetic, they require relatively high flux to operate. So, typically, ELCBs and RCCBs operate at 20 mA or more.

The typical ELCB/RCCB is built into a 230-volt circuit breaker and is located in the panel board.

I've never seen a test button on an ELCB/RCCB. Instead, they include a reset lever for resetting after either a ELCB/RCCB- caused trip or an overcurrent-caused trip.

In the USA, many professionals believe that the GFCI detects current in the ground wire. GFCI manufacturers support this myth by requiring the GFCI be only installed where a ground wire can be connected.

Because the GFCI/ELCB/RCCB operates on differential current, a ground wire is not essential to its operation. A GFCI operates equally well without a ground wire connected to it. I've done it! (This is not a recommendation or advice to install a GFCI contrary to manufacturers instructions; rather, I simply want to make the point that GFCIs operate on differential current, not on ground wire current.)

Richard Nute
San Diego