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Author Topic: Rock Singer Electrocuted On Stage  (Read 19740 times)

Stephen Swaffer

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Re: Rock Singer Electrocuted On Stage
« Reply #60 on: December 07, 2014, 09:11:22 pm »

Impressive (dead) famous name dropping aside, Kirchoff's current law refers to current into and out of a "single" circuit node, which by definition combines to net zero.
 

To what principle would I properly attribute the concept that the current in the hot and neutral conductors must balance?

Whether the node is a solder joint on a pc board or a skyscraper in downtown Chicago the principle holds.  I find that a lot of people are confused about electricity because they don't understand the basic physics involved-principles that to someone with your background are as taken for granted as the law of gravity-and that are always true.  I did not quote the law-nor do I feel "name dropping" out of place as anyone reading this can easily find more in depth information if they so desire.
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John Roberts {JR}

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Re: Rock Singer Electrocuted On Stage
« Reply #61 on: December 07, 2014, 09:20:44 pm »

How would the charging of a capacitor in a simple DC circuit affect current balance between the (+) and (-) conductors?
If there was a capacitor (with a diode rectifier) to charge up that cap, between hot and neutral, the current charging up the top of the cap, flows through and out the bottom of the cap.
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How about an inductive load on an AC circuit?
A reactive load can impart phase lead or lag between the voltage and current but that load is between hot and neutral so currents will still be equal.
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Do not either of these have the potential to imbalance the current without the presence of current leakage?

(Educate me!)

No as I described as long as the current in the hot lead is equal to the current flowing in the neutral lead the GFCI is in balance.

JR
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John Roberts {JR}

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Re: Rock Singer Electrocuted On Stage
« Reply #62 on: December 07, 2014, 09:51:08 pm »

To what principle would I properly attribute the concept that the current in the hot and neutral conductors must balance?
It would be the "principle" of the GFCI's particular circuit design (probably more than one way to execute a GFCI).
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Whether the node is a solder joint on a pc board or a skyscraper in downtown Chicago the principle holds.
Since you mention Kirchhoff there are several variants on his law, one for voltage around a loop must add up to zero, which is obvious because the voltage across a node must be zero, and another for all current into a node must equal the current leaving a node... Also obvious since the node can not create or destroy current.

There are probably multiple examples in nature similar to Kirchoff's current law node, (like the water flowing into a water pipe tee junction will equal the water flowing out of that tee... the tee can't create or destroy water) but an important given for his current law is we are talking about a single node  (his voltage law applies to voltages around a loop with multiple nodes but that is not remotely like a GFCI either).

 
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I find that a lot of people are confused about electricity because they don't understand the basic physics involved-principles that to someone with your background are as taken for granted as the law of gravity-and that are always true.  I did not quote the law-nor do I feel "name dropping" out of place as anyone reading this can easily find more in depth information if they so desire.
I am probably being pedantic, but I object to the mis-application of the well known law about currents in a single circuit node, to a more complex circuit better characterized as two conductors in series with the hot and return from an AC power source, to sense if any current that goes out to the load, does not come back. Any such lost current is considered a potential shock hazard.   

My advice for lurkers is to not get distracted by all my pedantry.. All we need to know about GFCI is that they compare the current flowing out of the hot lead into the load, to the current returning from the load in the neutral lead. If any current is lost from the load and does not find it's way home, the GFCI trips.   

JR

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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Art Welter

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Re: Rock Singer Electrocuted On Stage
« Reply #63 on: December 11, 2014, 10:42:56 am »

That's correct. Here's my No~Shock~Zone article on GFCI theory which includes diagrams of your explanation. http://www.noshockzone.org/rv-electrical-safety-part-viii-gfci/
Mike,

Thanks for referencing your pump analogy explanation, I was under the mistaken impression that the current difference measured was between neutral and earth ground in Ground Fault Circuit Interrupters.

Art
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Mike Sokol

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Re: Rock Singer Electrocuted On Stage
« Reply #64 on: December 11, 2014, 08:25:45 pm »

Mike,

Thanks for referencing your pump analogy explanation, I was under the mistaken impression that the current difference measured was between neutral and earth ground in Ground Fault Circuit Interrupters.

Art

You're welcome.

Yeah, when I first started playing with GFCI's years ago it was all terribly confusing. But once I got a look at a schematic and realized that the EGC path wasn't part of the sensing circuit it all made sense.

The water pump analogy is how I taught myself electricity when I was a young teen. Found it in an old (50's?) book about electricity and it really helped me sort out the idea of voltage, current and resistance. And it really helps when you're thinking about fault leakage paths for things like GFCI sensing circuits.

Now some old electrical graphics don't translate too well. I found this one last week while looking for an Ohm's Law chart for my students. Seems a little bit too creepy to me.
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Stephen Swaffer

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Re: Rock Singer Electrocuted On Stage
« Reply #65 on: December 11, 2014, 11:03:32 pm »


** While I have not taken any GFCI apart I can imagine a simple magnetic circuit with separate hot and neutral windings that are equal but opposite polarity. As long as 100% of the current flowing in the hot winding is matched by the current flowing in the opposing neutral winding, the magnetic flux will completely cancel out. Any imbalance will generate an incomplete cacellation of magnetic flux that a third sense winding can read and use to trip the circuitry to interrupt power.   
 

I have disassembled a few that went defective too quickly for my taste (I can get them replaced but still eat the time for the service call).  You are correct, if you consider a wire a winding.  Anyone who has used a clamp meter knows you have to separate hot and neutral to get a reading or the currents cancel out.  They appear to use a very high turn count CT around both hot and neutral conductors.  Deceptively simple for the level of safety it provides.  Newer ones include self test circuitry as well as the ability to sense if hot and neutral are reversed (if an egc is connected).

 
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Steve Swaffer

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Re: Rock Singer Electrocuted On Stage
« Reply #65 on: December 11, 2014, 11:03:32 pm »


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