View Single Post
  #18   Report Post  
Posted to alt.home.repair
jeff_wisnia[_2_] jeff_wisnia[_2_] is offline
external usenet poster
 
Posts: 177
Default Weird GFI problem - wired correctly but not tripping

blueman wrote:
stan writes:


On Jul 24, 4:01 pm, "Stormin Mormon"
wrote:

Much safer, now. Good job.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
.

"blueman" wrote in message

...

I fixed the problem by tracing upstream where I found that
the ground
wire had broken off in the box. Problem solved & thanks for
the help.


Thanks for posting the outcome. A broken ground; glad the OP found it.

BTW: I agree with the person who posted;
Quote: "If you'd read the entire thread, you would have seen that the
OP stated that
the GFCI trips normally when he presses the test button on the GFCI,
but fails
to trip when he presses the test button on his plug-in tester -- and
you would
have also seen an explanation of why this is so: the plug-in tester
shunts
current to *ground*, and *cannot* trip the GFCI unless there is a
functional
ground at the outlet.".

It seemed obvious the question was why didn't the 'test' feature of
the 'tester' work as expected!

Interesting thread and as often makes one think (and learn!). Thanks
for posting the original question.



Your welcome
And I learned a lot too -- it is always sobering to learn the
limitations of your test equipment (or any other limitations).

I wonder how many professionals (e.g., electricians, home inspectors,
city inspectors) let alone DIY'ers realize that:

1. A GFI tester can show the circuit being fine even though there is
no functional ground. Similarly a (digital) multimeter can read the
full 120V hot-to-ground. Both presumably due to induced currents.


I don't think that "induced" is quite the proper term to use for what's
happening there. "Current flow through capacitive reactance" would be
more correct.

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.


2. The test button on a GFI can work also without a functional ground.

It all makes sense retrospectively, but probably not something that
most people think about...