On 13 Mar 2011 01:57:15 GMT, ddl@danlan.*com (Dan Lanciani) wrote:

In article , zzzzzzzzzz ) writes:
| On Sat, 12 Mar 2011 16:36:36 -0700, Tony Hwang wrote:
|
|
|
| Dan Lanciani wrote:
| In , zzzzzzzzzz ) writes:
| | On Sat, 12 Mar 2011 13:52:58 -0800, David
| | wrote:
| |
| |Just a li'l anecdote for those who've always wondered what happens if
| |you wire a GFCI to protect "downstream" outlets wrong (all 2 of
| |you)--that is, if you mix up the "line" and "load" wires.
| |
| |The answer? Nothing.
| |
| |Installed a GFCI in a client's kitchen, thinking I'd need two, one for
| |each outlet on a sink counter. It became clear, though, that they were
| |in a chain, so I could protect both with just one GFCI. So I wired in
| |the GFCI, wiring the downstream outlet on the "load" side, ass-u-ming
| |that the position of the cables in the box indicated the upstream and
| |downstream wiring respectively.
| |
| |Wrong.
| |
| |When I turned on the power, the GFCI's LED lit, but I couldn't reset the
| |outlet, and both outlets were dead.
| |
| | Strange, when I made the same mistake the outlets worked normally but wouldn't
| | trip on a "downstream" fault. The differential current sensing was on the
| | wrong side of the device, so didn't detect the fault. I can't see how they'd
| | fail the way you suggest.
|
| Newer GFCIs are specifically designed to be idiot-proof in this respect.
| They aren't failing; they are just helping you. Although older GFCIs
| would not be damaged by the incorrect wiring, they wouldn't be able to
| shut off the power to the local outlet even if they trip.
|
| But how does that work? How does the GFCI know which side is line and load?

I don't know if they all work the same way, but the ones I have looked at
are pretty simple. They start in the tripped state. The reset button is
no longer a simple mechanical device; it is interlocked such that the device
cannot be reset unless there is power on the line side. You can probably
defeat the protection by installing correctly (or on a bench), pushing reset,
installing incorrectly, and then never pushing the test button. But who
would do that?

That works. Ingenious, even. Thanks.