[R-390] GFCI issues

[rbethman]

Actually, the "toroid" structure that the hot and neutral are wound 
through is a toroidal transformer.

There are wires wound inside the toroid.  These windings under normal 
conditions, only see the field as balanced.  Thereby cancelling out any 
flow.

Yet, should there be an imbalance, these windings would develop a flow 
and indeed send their output to the little solenoid and cause the trip.

You would really have to have one open and in your hand to see how 
ingenious, elegant, yet simple design and device that it is.

The test button puts a 15K ohm resistor in the circuit to one leg.  This 
causes the imbalance to cause it to trip.

The reason for the distinctive snap from pressing the reset button, is 
that it re-latches the solenoid assembly and locks it back open.

I'm glad I did open it just to satisfy my curiosity!

It also now makes MUCH more sense as to why two of them back to back 
would/could be problematic.

I don't see how they *couldn't* interact.

It was a pain to get through all of this, BUT it was very educational!

Bob - N0DGN

On 3/20/2013 8:22 PM, Bob Camp wrote:
> Hi
>
> Keep in mind that there is no way a two wire device can trip a working GFCI all by it's self. It simply can't generate an imbalance between the hot and the neutral. There's no place else for the current to go. In order for it to trip a GFCI, there *must* be a third path, generally to ground. Assuming you are holding the two wire device up in the air (and not underwater) the only place for the current to go is through you. It's not going through the air. If it's going through you, you *would* notice it.
>
> Bob
>
> On Mar 20, 2013, at 4:04 PM, rbethman <rbethman at comcast.net> wrote:
>
>> I used Mr. Hacksaw.
>>
>> I can now look at the circuit inside.
>>
>> The Hot and Neutral are wound through a toroid.
>>
>> There are a pair of wires coming out of the middle of the toroid. They go to a solenoid.  That solenoid, when it moves, trips the mechanical switch inside the GFCI and opens the circuit!
>>
>> It is definitely a Rube Goldberg thing to look at - but it DOES work!
>>
>> This is the GFCI that I removed from the Old Hair Dryer.  It has NO ground!  It is a two prong device.
>>
>> Bob - N0DGN
>>