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How to test GFCI plug?

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PEQ

PEQ

Electrical
Apr 10, 2019
8
I have a gfci plug for a small enclosure.

is there a way to force a trip to see if the GFCI actually works? The customer is asking for this.

Thanks!
 
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Yes; Google "GFCI tester" like I just did and follow the links...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
 
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I had googled how to test GFCI and all it showed was MANY people saying to press reset button.
 
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"GFCI test" and "GFCI tester" are two different queries...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
 
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Old school:
120 Volts / 0.015 Amps = 8000 Ohms
Take a resistor of about 5000 or 6000 Ohms and wire it between the hot (Narrow blade) and ground pin of a male cord end.
The GFCI should trip when the plug is inserted into the GFCI.
Note: The ground terminal of the GFCI must be connected back to the system ground to pass this test or a test with a commercially available tester.
BUT
A GFCI in good working order will provide personal protection even when the GFCI ground terminal is not connected.
An alternate test for a GFCI without a ground connection is to use the same resistor but use a wire to connect the hot terminal, via the resistor, to the system ground.
The GFCI works by comparing the current out on the hot line with the current returning on the neutral line. If the current out does not match exactly the current back, the GFCI assumes that there is a leakage to ground and trips off.
Houses wired before the 1950s use Romex that did not have a ground conductor.
At one time, some codes allowed these circuits to be upgraded for safety with the addition of GFCI devices rather than installing grounding conductors.
The GFCI does not require a connection to ground to function properly and a GFCI provides ground fault protection at a level of 0.015 Amps whereas a receptacle with code grounding and a 15 Amp breaker but no GFCI provides ground fault protection at a level of 15 Amps.
Any current in excess of 0.015 Amps from the hot to the system ground will trip a GFCI regardless of the path of the ground fault current.
Another advantage of a GFCI is that it may be used with equipment that is connected by an unpolarized plug or extension cord or with equipment that is connected by plug or extension cord with a broken or missing ground connection and still provide protection.
The GFCI may be installed at either the supply end or at the load end of a circuit and will still provide protection.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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So does pressing the TEST button on the GFCI receptacle do this very thing, or does it merely inject a pilot signal partway through the trip circuitry while not actually applying a high impedance ground fault?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
 
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crshears,

The tester that you indicated only tests whether the GFCI is working.

I am looking to trip the GFCI to make sure that it stops power until a reset is pressed.

Waross's idea might work.
 
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I'm confused...

Maybe it's just me, but my understanding of those GFCI testers is that they do what Bill is suggesting and prove that the GFCI is working by tripping it open and interrupting the power supply to the load.

How did you envision a GFCI tester proving that a GFCI is working without tripping it?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
 
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What is a safe way for a non-technical lab person (who barely knows what electricity means!) to trip the GFCI to prove that it works?

That is what I would like to know.
 
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It's generally not safe for non-technical people to perform electrical testing.
 
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I found the following:

"The Gardner Bender GFCI Outlet Tester...plugs into any standard 120-Volt outlet and indicates the wiring condition of the outlet. The GFI-3501 also has the ability to test any outlet protected by a ground fault receptacle to ensure proper interruption operation."

A lay person should be able to safely insert this tester into the receptacle, press the button, confirm the GFCI trips and interrupts the power supply to the protected loads, remove the tester from the receptacle, and return the GFCI to normal operation by pressing its reset button.

EDIT: if the expected result is not obtained, the lay person must promptly report this to a qualified electrician.
 
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Plug lamp into GFCI outlet, press the "TEST" button, watch light turn off. Press "RESET" button, watch light turn on?
 
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bwen08 has it. And yes pressing the test button is the UL listed CORRECT way to test GFI outlets. It simply and reliably causes a ground fault that a working outlet will trip correctly with.

If you have a GFI breaker and want to test outlets elsewhere then a commercial tester would be recommended. Bill's recipe would work for that too but is not so good for the general public. If you have a person capable of doing electrical things safely you can make a tester by acquiring a plug that can be installed on cords and instead just wind the appropriate resistor as Bill showed around the screws and then when you want to test an outlet you just plug it into the outlet of interest. This can be good when a GFI outlet is daisy-chained down the wall or on the other sides of a wall. Just looking at an outlet doesn't tell you if it's GFI protected or not but plugging the tester/test-plug in will test it.

Keith Cress
kcress -
 
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Keith,

In my experience, the GFCI receptacle test button works even on two-wire circuits with no ground wire. The test button cannot create an actual ground fault, but must cause a differential current.
 
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You're right stevenal that The Button works on 2-wire circuits. I have several unfortunately. The imbalance is created thru the same balanced current coil by simply adding another sensed wire thru it that is not compensated. The test current is created across the hot-neutral. It still tests the circuit perfectly.

GFI-Schematic_r6hoan.png


Keith Cress
kcress -
 
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The fancier plug receptacle testers include a button for testing GFCI receptacles; which presumably does the exact same thing as the button on the GFCI receptacle itself
032886910036.jpg


TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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The external tester would have to leak to ground rather than back to the neutral the way the test button can. With an open ground it might not trip a good GFI.
 
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Very good point IRstuff. For a moment I was thinking the same thing davidbeach wrote.
 
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