1. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    OK, I am also working with a master electrian on my home.
    And we are installing GFCI ... ( I totally get how 4way , 3 way , 2 way switches go , how regular recepticals go , regular circuit breakers go. But when it comes to the new GFCI and AFCI I don't fully under stand them.

    And I was asking him a question about the installation of these ....
    Which he said it had to do with the circuitary of the GFCI and AFCI....

    Here is the question
    I was being guided on how to install a GFCI he said you always use the line side to put the GFCI on the circuit and the load side if you are running more recepticals off of that.

    So I started asking him if you could run a GFCI directly to another GFCI... (like regular recepticals )
    And he said yes you run it from line to line...

    But then I asked him if you could go line to load or load to load with two GFCI.
    And he said you are not supposed to do that it screws up the circuitary of the GFCI and makes it trip or not safe...etc

    I am wondering why that is (I currently don't fully understand this and may be misinterperting him)
    Don't fully understand this line and load stuff of the GFCI or AFCI... basically for regular recepticals their is just eletrically common screws thats it no distinct line and load seperate screws)

    I was under the impression that all the GFCI was is a regular outlet with
    a built in circuit breaker to trip if the current thru the black wasn't the same current flowing out of the white. (which would mean their is stray current going to ground hence the name ground fault circuit interupter )

    So I must have to understand the circuitary of the GFCI itself to get the full picture...

    If anybody could explain this or point me in the correct direction it would be great thanks.
    Also I am wondering what the difference in using a GFCI breaker at the service panel instead of installing GFCI recepticals is ??? They sure cost a ton more is their any add safty or benfit to doing it the breaker way?
    The electrician didn't know for sure he said I have done them both ways a million of times now and the breaker ones are alot more expensive but couldn't tell me why they where?
     
    Last edited: Feb 26, 2010
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    I've not seen that style (they are built differently in the UK), but from your description, it appears they contain the actual GF circuit with both input (line) and output (load) terminals, plus the socket outlet connected to the Load side.

    The Load terminals could be used to connect additional plain outlets, which would be protected by the same GF unit.

    The Line terminals would be used for the supply and to daisy-chain to another outlet, whether the line input on another GF or to a plain outlet that did not need protection.

    When Ground Fault units were first introduced here in the UK, they initially replaced the incoming supply master switch at the fuse board ('Consumer Unit').
    If anything developed a fault, (or sometimes if just a light bulb failed), the whole house shut off and everything went black..

    The later system uses a 'split load' board, where things like lights, alarm system & anything on fixed wiring is on circuits coming from the main switch, and the central GF trip is seperately fed from the main switch and in turn feeds another set of circuits for socket outlet ring mains etc.

    Individual GF-protected outlets are sometimes used as well, these would typically be in locations where outdoor or 'wet' appliances would be connected, like in a garage or outdoor sockets fitted to a garden wall.

    If I remember correctly, the individual protected GF outlets are about three times as sensitive as the central GF unit.
     
  3. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If you look at the GFCI as a load controller, it becomes easier to understand. Inside, the LINE terminals tie to set of mechanically latched contacts. The RESET button closes the contacts andthey are latched mechanically by the armature of the FAULT relay. Current from both the HOT and the NEUTRAL line flows through a small torroid transformer. If both currents are equal, as they should be, there is little or no output from that transformer. If, on the other hand, there is a ground fault, meaning that some current is going to ground through a path other than the returning neutral line, enough voltage is developed in the torroid to activate an electronic circuit that will activate the FAULT relay. This causes the internal contacts feeding the receptical (and the LOAD terminals) to open thus preventing any power from leaving the GFCI unit.

    As for the units that mount directly in the Breaker Panel, they contain the same type circuit but will have a WHITE pigtail which will tie to the NEUTRAL BUS BAR, and an extra terminal for the WHITE NEUTRAL wire feeding the load. Internally, the current being sent to the load is compared to the current returning from the load. Operation is like the description above.

    Hope this helps you to understand what they do and how they do it.
     
  4. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
    4
    Yes , it does and I even looked at the circuitary of one and it is not very hard to understand / build one.

    But my question is why are the breaker ones so much more expensive then the receptical ones?
    I cann't see them providing anything more other then the abilty to also be like a regular breaker to detect not only ground faults but shorts ,or overload?

    But the price difference still shouldn't be that much more then the receptical ones since regular 15amp breakers can be bought for $5 or so.
    so the gfci breakers = gfci detector + regular breaker.

    Thanks for any clarity.
    Just curious do they make GFCI for 240volts and hire or are these breakers/recepticals just used predominately on 120vac power outlets.
    Stands to reason it would be safer to make them for all the voltages ...
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    I can't explain the cost difference between the recept type and the breaker type other than volume of sales of each type. As for the 240V, since your info doesn't say what part of the world you live in, I can't say for sure. If you live in the US, for example, YES, there are two pole 240V GFCI breaker types sold. I have a 60A/240V GFCI installed that feeds my Hot Tub. (A code requirement where I live)
    Other methods can be used to provide the benefit of a GFCI simply by monitoring the current differences between the supply and return. As an example, for a 3 phase motor, if all three power lines go through a single torroid, the output of that torroid can be used to trip a ground fault relay and it, in turn, drop out the primary relay..
     
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