GFCIs on 2 wire circuits

[dscott2]

I was taking the NACHI electrical inspection online course today and under the topic "GFCIs on 2 wire circuits" it states "There is a common misconception that GFCIs only work on grounded circuits. This is not entirely the case." My question is when would a GFCI work on a 2 wire circuit?

[Michael Larson]

Originally Posted by dscott2

I was taking the NACHI electrical inspection online course today and under the topic "GFCIs on 2 wire circuits" it states "There is a common misconception that GFCIs only work on grounded circuits. This is not entirely the case." My question is when would a GFCI work on a 2 wire circuit?

The GFCI does not rrequire a ground to function as it is sensing the current in both the supply and return leg is within 5 mA of each other.

If not it opesns the circut.

[dscott2]

So it's ok to install a GFCI on a 2 wire circuit. Thanks Michael

[Terry Clayton]

If the AHJ will allow it

[Michael Larson]

Originally Posted by dscott2

So it's ok to install a GFCI on a 2 wire circuit. Thanks Michael

Yes but the outlets have to be labeled as not providing a safety ground.

[James H. Bushart]

Originally Posted by tclayton

If the AHJ will allow it

St. Louis County still uses 2005 NEC and does not modify this rule in their own code. All St. Louis municipalities, likewise....but get a hold of the actual code for the City of St. Louis. They write their own electrical code and this may not be allowed in it.

[Frank P. Newman]

...and receptacles for certain applilcations are required to have a ground, so getting around the three wire requirement with a GFCI has only limited opportunity.

[dscott2]

Where I usually find this condition is at kitchen counter outlets and bathroom sink outlets.

[Chuck Evans]

GFCI works fine on a 2-wire circuit, it's just your typical tester that won't work. The tester needs a ground to be able to simulate a leak to cause it to trip. It will still trip if there is an actual current leak or if you use the device test button which does not require a ground to work. I believe that the on-board test button uses a resistor to simulate a leak.

Most all of the GFCI outlets I have ever purchased come with two sets of labels "GFCI Protected Outlet" for downstream outlets and "No Equipment Ground" for when they are used to provide a 3-prong outlet on an ungrounded system.

NEC allows use on ungrounded systems, but local codes may not.

[Christopher Currins]

Replacing Receptacles to Meet the NEC

The NEC requires receptacles installed on 15 and 20 ampere branch circuits to be of the grounding-type and it requires the grounding contacts of those receptacles to be effectively grounded to the branch circuit equipment grounding conductor [210-7]. However, the Code allows the installation of any of the following installations when replacing a 2-wire nongrounding-type receptacle where no ground exists in the outlet box [210-7(d)(3)], Figure 9/10:

(a) Replace the 2-wire receptacle with another 2-wire receptacle.

(b) Replace the 2-wire receptacle with a GFCI-type receptacle and marked the receptacle with the words “No Equipment Ground.”

(c) Replace the 2-wire receptacle with a grounding-type receptacle where protected by a GFCI protection device (circuit breaker or receptacle). Since the grounding terminals for the receptacles are not grounded, the receptacles must be marked with the words “GFCI Protected” and “No Equipment Ground.”


Author’s Comment: The equipment grounding conductor serves no purpose in the operation of a GFCI protection device, and therefore it has no effect on the function of the GFCI test-button.

[Paul W. Abernathy]

Yep, lets not forget the structure of the NEC and other documents. Even the "Codeists" like myself need to remember...USBC, IBC,IRC.....then NEC....the NEC is simply a standard to which is referenced so at the end of the day....your statewide building code comes first, then the international codes and then our little NEC.

While the NEC may allow something, the IRC, IBC or the USBC may not.