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Old 09-24-2012, 03:55 PM  
Wuzzat?
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Originally Posted by CallMeVilla View Post
two GFCIs on the same circuit run will cause conflicting trips.
The one with the more sensitive trip curve at the value of the leakage current will trip first and make troubleshooting confusing.
That is, which one trips first may depend on how many mAs of leakage you have.

BTW, the trip curve given by UL's 943 standard is a max value and seems to say that almost everyone can stand 20 mA through their body for one second without harm.


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Old 09-24-2012, 05:50 PM  
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GfI are great if you short power to ground but if you touch white and black you are getting plenty and the gfi does not trip. Bin there done that



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Old 09-24-2012, 07:28 PM  
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Building a GFCI that can tell when a person is across the line may be more difficult than building a reliable AFCI.

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Old 09-24-2012, 08:59 PM  
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The part I don't understand is you can still buy things with a two prong plug and with plastic plumbing the sink is not grounded so if you drop that aplience in the sink, it will trip the breaker but not as fast as gfi but the gfi will not trip.

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Old 09-25-2012, 01:10 PM  
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The part I don't understand is you can still buy things with a two prong plug and with plastic plumbing the sink is not grounded so if you drop that aplience in the sink, it will trip the breaker but not as fast as gfi but the gfi will not trip.
When I put a hand mixer held by the cord into the water in a grounded concrete basement sink it didn't trip the breaker. The mixer just slowed way down because the motor cooling propeller now had to push water around instead of air so the current draw must have gone up to almost a stall current value but not enough to trip the breaker.

If that mixer were on a GFCI circuit I guess it would have tripped it, but not if all the current coming in the hot line went back out the neutral line. The closer the mixer is to the sink drain, the more current the drain would divert from the neutral line.
A GFCI is looking for an imbalance in what goes out and what comes back and it assumes the difference it sees is due to somebody being grounded and getting a shock.
It's a differential milliammeter with a go/no-go, trip/no-trip, time-delay output, with a higher differential current giving a shorter trip time.
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Old 09-25-2012, 05:15 PM  
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That could have been a shocking experience.

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Old 09-26-2012, 10:04 AM  
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Yeah, I should have hired a stunt double to do it. Or an ex-wife.

The best shock I ever got was while standing barefoot on a concrete floor trying to force a four prong auto radio vibrator into a four prong tube socket from an ancient radio set. It was probably hundreds of DC volts and many mA.

And the kid standing next to me couldn't imagine what all the fuss was about.

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Old 09-26-2012, 05:19 PM  
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Don't drop a concrete vibrator in the water and then think you can go pick it up.

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Old 09-27-2012, 10:12 AM  
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Don't drop a concrete vibrator in the water and then think you can go pick it up.
I guess grabbing it is the easy part.


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