Outlet tester puzzle

[Percival P. Cassidy]

I just replaced a regular outlet by a GFCI outlet. A GB outlet tester with GFCI tester shows that there is no ground (just the same as before I changed the outlet -- I'll try to solve that problem later: there is a bare copper wire connected to the metal box and to the outlet's green screw, but it must be disconnected at the other end), BUT pressing the outlet tester's GFCI Test button still trips the breaker. I thought that a ground connection was necessary for the test button to work.

Perce

[CJT]

Nope.

[Chris Friesen]

According to the diagrams here

the test button diverts some current from hot to ground to cause the hot/neutral conductors to not carry the same amount of current. Without a ground, how would the test button work? Where does the diverted current go?

Chris

[Chris Friesen]

Doh...should learn to research first. Found an alternate design where the test button diverts some current around the sensing toroid back to neutral such that the toroid sees unbalanced current even though it is actually balanced for the receptacle as a whole.

Works just fine with no real ground.

Chris

[avid_hiker]

Could be grounded to such as the water pipes rather than the ground in the main box.

[spamTHISbrp]

So when you push the test button on the outlet tester it trips? (or the built-in GFCI test button?)

The external tester leaves out bypassing the toroid, I assume the GB tester shorts hot-to-gnd through a resistor, so there must be enough of a leakage current through the 'open' ground to trip the GFCI (as far as I can reckon)

Dave

[Toller]

I doubt that; if the tester shows an open ground there wouldn't be enough of a connection to simulate a ground fault through the tester. I would guess that the tester is wrong about the open ground. Has the OP tested it on other outlets that are grounded?

[Chris Friesen]

See my other post. If the self-test shunts some current from hot to neutral bypassing the toroid, you could have a self-test that works fine while the external tester wouldn't be able to work due to a lack of a ground path.

Chris

[Goedjn]

Didn't we just play that game? You couldn't give it two days before starting again?

[CJT]

Look at the diagrams again. The test button goes from hot to NEUTRAL through a resistor.

[Percival P. Cassidy]

No, we didn't. What I asked previously was about GFCI outlets or breakers on an Edison circuit. This is not an Edison circuit.

Perce

[Tom Horne, Electrician]

Chris That scheme only applies to the built in test circuit in the GFCI itself. A plug in tester does indeed need a ground in order to work but the ground only has to be good enough to carry six milliamperes. That would not make it a satisfactory low impedance pathway back to the source via the main bonding jumper.

[Chris Friesen]

Yes, certainly.

Something that this whole discussion has prompted me to wonder...has anyone ever heard of a tester (with a long heavy cable) that would plug into the service panel directly that you could use to *really* test outlets? Could be used to test non-grounded GFCIs, test for floating ground, put 13A through each of the leads, measure voltage drop under load, etc...? Seems like it might be useful to highlight possibly sub-standard circuits.

Chris

[Mark Lloyd]

And the diagram appears to show this incorrectly. It shows both sides of the resistor connecting to the LINE side of the transformer, when you it needs to connect to one of each side. The real GFCI I looked at did so.

[Jeff Wisnia]

I promise to stay out of this one.

Jeff

[Bud--]

Ecos Electronics made testers that used a current pulse to test circuit grounds. Didn't need an external connection. Don't know if Ecos is around anymore but the testers probably show up on eBay.

-- bud--

[Tom Horne, Electrician]

The Ideal Suretest does that without a long cable.