Need help with this circuit.

Discussion in 'Electrical Forum discussion & Blog' started by AWeitzmann, Apr 5, 2014.

  1. AWeitzmann

    AWeitzmann New Member

    Messages:
    8
    Location:
    NJ
    This circuit has stumped me and its driving me nuts. The main limitations are the placement of the feed, the fact that there can only be 3-wire between the two single pole switches and cables must be ran in only the manner they are shown. I know it is possible but cant figure it out.
    WIN_20140405_140832.jpg
  2. bluebinky

    bluebinky Member

    Messages:
    393
    Location:
    Santa Clara, CA
    If you mean that switch "A" switches light "A" and "B" switches "B" with only three current carrying conductors between the switches, then I don't believe there is a way to do what you want with conventional switches.

    The choices are 1) use some kind of electronic controls/switches, 2) violate the code to make it work, or 3) find a way to add another conductor.

    It can be done. Just not legally:cool: Sorry, I don't feel comfortable saying how unless one of the moderators gives the go-ahead.
  3. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,126
    Location:
    Houston, TX
    I am confused.

    Are these in series or parallel ?

    Watt are you trying to do ?


    AC, DC or FM ?
    Last edited: Apr 5, 2014
  4. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    "there can only be 3-wire between the two single pole switches"

    Why? You don't have conduit running between them? Is that impossible? You could get four conductors and a ground into conduit.

    But if you want or need NM and have the walls open, there IS such a thing as NM with four conductors and a ground. Good luck finding it. And good luck finding a supplier that will cut you off 17 ft or what ever it is you need.

    Why does it need to be one cable? Why must the middle cable that is 3 conductor even going from Switch A to Load A thru box B?

    Why cannot two lengths of two conductor serve between box A and B?
  5. AWeitzmann

    AWeitzmann New Member

    Messages:
    8
    Location:
    NJ
    First there is a NM with 4 conductors it is called x/2/2, x/2/2. x representing whatever size wire you want. It has two of each conductor and a ground. Kinda of expensive but it sold at electrical supply stores.

    Second I am in Electrical School and since I powered through every other circuit that my teacher gave me, he decided to throw this at me. Those are the limitations that were put on me and I was assured it would work with no code violations, and with the exact wire I was instructed to use. The only hints i was given was that it has a lot to do with kirchoff's law. I understand it but not sure how it applies.
  6. AWeitzmann

    AWeitzmann New Member

    Messages:
    8
    Location:
    NJ
    This circuit was given to me by an instructor at my school and I was told that it can be done with no code violations and with only what is shown on the circuit. I am fairly decent at wiring, which is why he threw this at me for a challenge. Ive looked over for a number of hours and i just cant figure it out. I know i would need to have two switch legs between A and B (one for each switch), the ungrounded conductor to power B and the neutral for light A. I told him this and all he would tell me was its used for conveyor/light circuits all the time and it has a lot to do with kirchoff's law. I understand the law but not how it applies
  7. bluebinky

    bluebinky Member

    Messages:
    393
    Location:
    Santa Clara, CA
    This question is vaguely familiar, but I still don't understand the exact requirements. How does everything interact?
  8. AWeitzmann

    AWeitzmann New Member

    Messages:
    8
    Location:
    NJ
    They interact just as shown. Switch A controls light A and switch B controls light B. 14/2 between the lights and the device boxes and one and nothing but the one 14/3 running between device boxes. With the feed coming in through device box A. I have kept looking over it and I'm pretty sure I've come up with it . If anyone can confirm you can switch the grounded conductor as opposed to the ungrounded conductor with a spst switch, then I definitely know how to do it. I just started going though the code book and as of now I cant seem to confirm or refute this. I can post my diagram if me or someone else can confirm that its legal and if not, I'm back to square one.
  9. AWeitzmann

    AWeitzmann New Member

    Messages:
    8
    Location:
    NJ
    Never mind. NEC section 404.2(B) states: "Switches or circuit breakers shall NOT disconnect the grounded conductor of a circuit." I'm not any closer than I was and starting to think its not possible.
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,997
    Location:
    New England
    You're only supposed to switch the hot lead. It isn't hard to do if you can switch the hot on one lamp, and switch the neutral on the other with the wires available. This assumes you're using simple on/off switches, and not some 3-way switches, which would give you other options. Other than that, I'd have to play with it a bit more.
  11. Reach4

    Reach4 Active Member

    Messages:
    2,231
    Location:
    IL
  12. bluebinky

    bluebinky Member

    Messages:
    393
    Location:
    Santa Clara, CA
    240/208V devices + conduit? You could always pull the neutral later, if needed. That would satisfy the code...
  13. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,126
    Location:
    Houston, TX


    You say using "Single pole" switch.

    Are they SPDT double throw, or SPST single throw ?

    You have 2 S1s ?
  14. AWeitzmann

    AWeitzmann New Member

    Messages:
    8
    Location:
    NJ
    Spst

    They are two spst switches in the diagram but as i thought about it he never actually restricted me to using any one type of switch. He plainly said that switch A controls light A and Switch B controls light B. I just assumed, one location and went for the spst. Not sure if this makes a huge difference in the circuit but we are not restricted to only spst.
    Last edited: Apr 6, 2014
  15. AWeitzmann

    AWeitzmann New Member

    Messages:
    8
    Location:
    NJ
    He never actually restricted me to using spst, not sure if this make a difference. Im going to start messing with other types of switches now but use whatever type of switch that would make it work with no code violations.
  16. AWeitzmann

    AWeitzmann New Member

    Messages:
    8
    Location:
    NJ
    We have 208v + 208V devices in school and also all the conduit and THHN i could ever want....not sure how it would get me past the whole switching the neutral part of it though.
  17. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,997
    Location:
    New England
    If you make it a 240vac circuit, you do not have a neutral, and you can make it work with simple spst switches. The only issue, and it's 'normal' is that you still have voltage at the lamp fixture, but you are switching only a hot lead.
  18. Homeownerinburb

    Homeownerinburb New Member

    Messages:
    525
    Location:
    Los Angeles, CA USA
    Jim,

    I'm pretty sure you cannot shut off a 240v load with a single pole switch. One needs a two pole switch. Such switches exist. Assuming one has a 240v light bulb fed by opposite hots, one needs to interrupt both hots when shutting it off.

    Please don't ask me to cite chapter and verse.
  19. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,126
    Location:
    Houston, TX
    The Voltage was not given.

    That was maybe pulled from a textbook and is a 12V or Low Voltage circuit example. Has nothing to do with house wiring.

    It is used for teaching series and parallel circuits.
  20. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,997
    Location:
    New England
    It would certainly be safer with dpst switches.
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