Testing GFCI's - A Philosophical Discussion


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!
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DerbyDad03 wrote:

You test them when you install them and you test them when you have reason to suspect they have been damaged. Outside of that you don't test them despite the "Test Monthly" nonsense printed on them. Even in large commercial buildings with full time on site electricians I have never seen any GFCI testing. IR scans of distribution panels, regular tightening of connector lugs, etc., but no GFCI testing.
Pete C.
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DerbyDad03 wrote:

That's true of any device, electrical or mechanical. The identical condition is true when the truck driver is asked to pull over and do a brake/air check at the top of a long downhill stretch prior to starting the descent...or the scheduled test of the Class 1 safety system in a nuclear power plant, or any other system you care to name.
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Absolutely true.
Tommorrow I'll post my philosophical musings on the taxpayer dollars spent on those "Trucks Test Brakes" signs. Sure seems like a waste. <g>
dpb wrote:

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DerbyDad03 wrote:

Perhaps, but I've heard of at least one truck driver who was very grateful for the sand runaway truck ramp at the end of the slope. Could have damaged a lot more than his underwear had it not been there. Also note that those trucks pay a much larger share of the roads maintenance costs than you do in your car.
Pete C. (I'll probably be a truck driver eventually, once we've managed to outsource pretty much every other job...)
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It's probably good to exercise all your valves in your plumbing and test your GFI's once a year. I test mine at each outlet with a resistor.
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Pete C. wrote:

Yep... :)
The ramps on I-40 east near Black Mountain west of Asheville in NC have always had recent signs of activity when I go by there...
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There has been research that found that the contacts in circuit breakers and GFI breakers can fuse together with time and corrosion. The result is a breaker that may trip at a higher load than rated or may not trip at all. When you test a GFI, you open the points and the corrosion effect has to start over. From what I read, you really only need to trip a circuit breaker or a GFI about once a year to prevent this from happening. Brad DerbyDad03 wrote:

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So then shouldn't the label say "Exercise Monthly" as opposed to "Test Monthly"?
Brad wrote:

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DerbyDad03 wrote:

Not in the lard ass US, where exercise is an obscene word...
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http://www.codecheck.com/codecheck_resources_electr.html#shock
DerbyDad03 wrote:

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What, specifically, are asking us to look at?
buffalobill wrote:

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Instead of replying on list, Chris cluttered my inbox with, amongst other ramblings,
"Heck, if you're going to worry about stuff, why not worry about the airbags in your car--you have no way to test those until they're actually needed..."
I don't recall posting that I was "worrying" about anything. I simply made some points to start a fun discussion and it appears that I accomplished my goal.
DerbyDad03 wrote:

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how about testing circuit breakers by applying too high a current?
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I did that after I bought my house
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DerbyDad03 wrote:

Sorry about that...I had intended for that to go to the list and was actually wondering why I hadn't seen it.

I would submit that if one is not confident about something, then you have some doubts as to its effectiveness. Add to that the sarcastic "sleep well", implying that we shouldn't, and I don't think my comment was too far off.
Chris
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Chris Friesen postulated: - I would submit that if one is not confident about something, then you have some doubts as - to its effectiveness.
Doubting something's effectiveness is not the same thing as worrying about it. I doubt that many of the health aids they sell on late night TV are effective, but I sure don't worry about them.
- Add to that the sarcastic "sleep well", implying that we shouldn't, and I don't think my comment - was too far off.
What keeps other's up at night may not be the same thing that keeps me up at night. Perhaps I was just trying to instill a little worry in others. <g>
Chris Friesen wrote:

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Basic statistics require point 3:
3 - A GFCI that is 10 years old and never been tested is less likely to trip on a fault current. Why? Because, if it had failed to test over the 10 year period, presumably it would no longer be in the statistical pool.
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You test a GFI without a load so no arcing occurs on the contact unlike a circuit breaker that requires testing a greater than full load. Out of curiosity has anyone had a GFI that didn't trip on push to test or with an external short to ground?

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