I was pondering the concept of "monthly testing" of GFCI's the other day, basically trying to determine if it had any merit. Here are my thoughts...
What does a passing testing of a GFCI tell us? It tells us 2 things:
1 - That the testing circuitry worked at the time of the test; and 2 - Had there been a fault in the last month, there's a high probability that it would have tripped.What it doesn't tell us, in any certain terms, that the device will work the *next* time there is a fault. A GFCI is an electromechanical device and the possibility exists that the test we just performed was the last time that particular unit was going to work.
Granted, if it fails the test, we know we should replace it, so we're really checking for a failed device, not a working device. Perhaps we should feel better (read: relieved) when the test fails, because we have the opportunity to replace the failed device. Ah, but wait - once we replace the device and test it, all we really know is that it passed it's initial test - we still don't know that it will work when it is needed.
You know that disclaimer the investment folks always use - "Past performance is not a guarantee of future results"? It seems to me that the same holds true for a GFCI.
I submit that we should not feel confident that a GFCI will protect us just because it passed the test. In reality, all we can do is look back and say whether or not it would have protected us since the last test.
Sleep well!