GFCI Protection

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rmonroe

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I had a production associate come to me with a question in regards to a GFCI. He said recently he had a safety meeting, which our company sponsors monthly. The topic of GFCI came up and the instructor stated, according to this employee, that using a GFCI outlet and plugging let?s say an extension cord with a GFCI built into it would cancel out the protection.

Thanks

rmonroe
 
The instructor needs to study how GFCI's work if he really said this. Your friend may have misunderstood. A GFCI measures the current going out on the hot conductor and compares it to the current returning on the neutral or grounded conductor. If the two values differ by more than a set value of miliamps (often 7) the device will open the circuit. How would having two current measuring devices installed in a circuit prevent them from operating? Could you use two amprobes on a circuit at the same time? Of course, and this is the same principle.
 
I agree with haskindm. It would be like saying that if you see a road sign saying "Speed Limit 30 MPH" on one block, and then you see an identical sign on the next block, that somehow the second sign cancels out the first, so you can go as fast as you like. It just 'taint so.
 
haskindm is correct. Just to add a little more evidence, I have encountered situations were a gfci receptacle has been installed at a location, say an outside outlet, but was also protected by an upstream gfci receptacle such as in a garage. The gfci's both work just fine, as they should. This is not the best design since the upstream gfci may have a slightly lower trip threshold and will trip rather than the gfci closest to the fault, thus potentially causing some confusion as to why the receptacle has no power. But having gfci's in series does not cause them not to work.
 
charlie b said:
It would be like saying that if you see a road sign saying "Speed Limit 30 MPH" on one block, and then you see an identical sign on the next block, that somehow the second sign cancels out the first, so you can go as fast as you like. It just 'taint so.
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It's not??? D-oh!


eprice said:
But having gfci's in series does not cause them not to work.
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No, but it makes for some interesting troubleshooting calls.
 
charlie b said:
I agree with haskindm. It would be like saying that if you see a road sign saying "Speed Limit 30 MPH" on one block, and then you see an identical sign on the next block, that somehow the second sign cancels out the first, so you can go as fast as you like. It just 'taint so.
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You mean 30 + 30 doesnt equal 60mph.
 
rmonroe said:
I had a production associate come to me with a question in regards to a GFCI. He said recently he had a safety meeting, which our company sponsors monthly. The topic of GFCI came up and the instructor stated, according to this employee, that using a GFCI outlet and plugging let?s say an extension cord with a GFCI built into it would cancel out the protection.

Thanks

rmonroe
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Sounds like money well spent on this instructor
 
brian john said:
.....what you're trying to tell me that doing 60 in my neighborhood in unacceptable??
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I don't care what you do in your neighborhood....but you better keep it under 25 in mine ;)

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GFCI Protection

eprice said:
haskindm is correct. Just to add a little more evidence, I have encountered situations were a gfci receptacle has been installed at a location, say an outside outlet, but was also protected by an upstream gfci receptacle such as in a garage. The gfci's both work just fine, as they should. This is not the best design since the upstream gfci may have a slightly lower trip threshold and will trip rather than the gfci closest to the fault, thus potentially causing some confusion as to why the receptacle has no power. But having gfci's in series does not cause them not to work.
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This happened to me last week. Inspecting a final on a new house,I tried to trip the outside gfci outlet,it wouldn't trip but it lost power. It had double protection so double gfci protection does work but not a good idea. In this case the inspection failed and created a call back for the electrician. It could have resulted in a reinspection fee, but otherwise the guy did a good job si I didn't charge one.
 
romeo said:
This happened to me last week. Inspecting a final on a new house,I tried to trip the outside gfci outlet,it wouldn't trip but it lost power. It had double protection so double gfci protection does work but not a good idea. In this case the inspection failed and created a call back for the electrician. It could have resulted in a reinspection fee, but otherwise the guy did a good job si I didn't charge one.
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Technically, the installation should have passed.
 
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