Can a 3way switch short?

Discussion in 'Electrical Forum discussion & Blog' started by Tollerplumbing, Aug 29, 2013.

  1. Tollerplumbing

    Tollerplumbing New Member

    Messages:
    7
    Location:
    WNY
    I have a 30 year old house that is for sale. The realtor told me that the lights in the bathroom didn't work. I found the circuit was shorted. After checking 4 outlets and 9 switches I found that removing the very last item, a 3way switch, fixed the problem. I replaced the switch and all is well. But then I tested the switch and it seems to work properly.

    The switch is in a very stupid place and I didn't even know it existed; I only found it because I knew there had to be 2 3way switches and hunted down the second one. I never used it and doubt the previous owner did either. Just maybe someone at an open house flicked it for the first time ever, shorting the circuit.

    So my question...
    Is it possible for a 3way switch to cause a short? I don't really see how; I can see it not working, but I don't see how it could cause a short; especially since it seems to be working properly now.
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,542
    Location:
    North Carolina
    In your statement you made the remark that you had never used it. Is it possible that it was miswired in the first place?
  3. DonL

    DonL Jack of all trades Master of one

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    If a light switch don't short then the light never comes on.


    Be careful playing with electricity.
  4. Tollerplumbing

    Tollerplumbing New Member

    Messages:
    7
    Location:
    WNY
    I don't think so. There were just 4 wires in the box and I wired the replacement switch up exactly the same, and it worked normally then.

    The only possibility I can think of, other than a defective switch, is that the ground wire was excessively long. It might have been making contact with one of the traveler terminals, and that would be a short; but I didn't see that when I opened the box. Maybe I missed it.
  5. Tollerplumbing

    Tollerplumbing New Member

    Messages:
    7
    Location:
    WNY
    A short normally refers to creating an unintended path, generally to ground. Completing an intended circuit would not be a short.
  6. jwelectric

    jwelectric Electrical Contractor/Instructor

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    2,542
    Location:
    North Carolina
    This is what I was thinking the problem would have been but if this were true it would not have been a short it would have been a fault to ground called a ground fault.
    A short circuit is when you have one hot touching another hot or as Don pointed out the switch shorts the circuits causing the light to burn. Yes I know this is a play on words but being technical correct means a lot when dealing with current flow.
  7. Tollerplumbing

    Tollerplumbing New Member

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    Location:
    WNY
    A short to ground is when a hot contacts a ground; it is a universally recognized term.
    On the other hand the term "short" is never used to refer to an intended circuit; it is always accidental.
    I hope you guys are just having some fun, rather then really being ignorant, but I won't be coming back here either way.
  8. Homeownerinburb

    Homeownerinburb New Member

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    Location:
    Los Angeles, CA USA
    And diplomacy scores again.
  9. DonL

    DonL Jack of all trades Master of one

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    Location:
    Houston, TX

    Sorry you have a attitude.

    Many light switches do not have anything to short to. If the switch shorts then the light stays on, Not off.

    Or if it has a short and it is grounded it should Blow a Fuse or Pop a breaker. If not then it is not protected properly.


    Been Nice knowing Ya.


    DonL
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,542
    Location:
    North Carolina
    Anyone who works in the electrical field knows what a ground fault is and how to remedy the problem.
    250.4(A) (5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.
    All a switch does is short the open of the circuit or closes the path of the circuit so the light will emit
    I have spent more time in this field than you are old and about that many years standing at the front of a class. My wall is covered with papers from different colleges stating the amount of knowledge I have so no my friend I don’t think ignorance comes into play here with me.

    This is a choice that only you can make
  11. bluebinky

    bluebinky Member

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    406
    Location:
    Santa Clara, CA
    I have over 300 university/graduate credits, but none of them are in "ego management" or "diplomacy". Here's my shot at it...

    All three hot (non-bare) wires would see power during normal operation, even if the switch in question was never touched. The problem could be that the switch suddenly failed internally and shorted the hot terminal(s) to the ground lug, but that doesn't sound likely to me. Have any of you guys with lots of "field experience" ever seen that?

    To me, it sounds like wires touching somewhere that was "fixed" when things were moved around as the switch in question was replaced. Unless it can be verified with and ohmmeter reading zero between the ground terminal and at least one of the hot terminals on the "broken" switch, more investigation is needed.

    For safety (and liability), I would recommend someone licensed and insured looked at it unless the cause can be verified.

    Just for kicks, my understanding of the origin of the usage of the word "short" is sort of like landing short of a runway -- an unintentional return path physically "before" the intended load.
    Last edited: Sep 1, 2013
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
    New England
    FWIW, every switch is shorted once you turn it on...it connects one lead to another. The time when a short causes problems is when you short-circuit power to a place it is not designed to go without a load, such as directly to ground. Now, few switches can do that internally, since they normally only switch hot, or power, not neutral or ground connections, at least in residential situations.
  13. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,542
    Location:
    North Carolina
    Gentlemen,

    Ever hear if a Ground Fault Circuit Interrupter? It is the receptacle in your bathroom or over your kitchen countertops. It is not a Short Circuit Interrupter.

    There is a big difference between a short circuit and a ground fault. A ground fault is the hot having a path to ground be it the equipment ground or through you to earth.

    A short circuit deals with hot and hot as when the switch is turned on it shorts the hot to the hot causing the light to work or it is hot to hot causing the fuse to blow.
  14. DonL

    DonL Jack of all trades Master of one

    Messages:
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    Location:
    Houston, TX
    Really when you read the original post, it sounded like a open to me.

    If it would not light, That would be a open.

    Maybe a GFCI was tripped. And after working on it the breaker or outlet got reset somehow. Or you had a loose wire at the switch. Both are OPENs, and can cause the same symptom.

    Short Circuits Trip Breakers.


    Is the Horse Dead Yet ?
  15. bluebinky

    bluebinky Member

    Messages:
    406
    Location:
    Santa Clara, CA
    Really bad posting here guys...

    The OP said "shorted", and that removing the switch "fixed the problem" -- most likely meaning that the breaker kept tripping. No one here has offered an answer to the question do switches "short out". I have never seen one do so (at least not to ground), but my experience is limited to perhaps a few thousand -- way less than those of you who have worked with the stuff every day for decades...

    Switches do not "short" and "unshort" during operation -- they open and close (or make and break). A normally operating switch is no more a short by itself than is a piece of wire.

    A "short" does not mean zero ohms or even necessarily close to it. In some applications, a 100 megohm resistance would be considered a short, while in others much less than an ohm for a load would not be. A short is a current path in the wrong place. We have slang terms like "leakage" and "dead short", but these need a context to have meaning.
  16. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,542
    Location:
    North Carolina
    Short in electrical terms means to bridge or close. Ground plays no role in a short.

    In the field we become lazy and misuse terms. A good one to look at is the battery in our cars. From birth we are taught to remove the ground before removing the positive terminal of the battery in order to not shunt the positive to the frame of the car with the wrench we are using to remove the positive terminal.

    Well my friends there is no such thing as ground in a car as defined in the NEC or should an electrician ever refer to the negative terminal of a battery as ground.

    What was being talked about in the original post was a ground fault if the equipment grounding conductor was touching one of the travelers, not a short. The switch shorted the circuit and should the light bulb have been replaced with an Edison base fuse the fuse would have explained that the switch was shorting the circuit. But instead we have installed a load, the bulb, which consumes the energy of the shorted circuit so instead of tripping the overcurrent device we have light.

    Understanding terms makes discussing electrical theory much easier.
  17. bluebinky

    bluebinky Member

    Messages:
    406
    Location:
    Santa Clara, CA
    There are lots of ways to use the term "short", but I don't agree that saying "The switch shorted the circuit..." is a valid one. Oh well, I guess I'm outnumbered on this one by some people I've grown to respect.

    I'm still wondering, JW, have you ever seen a switch fail internally and cause a ground fault? The few that I've broken apart make me believe that there would have to be obvious visible damage.
  18. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,542
    Location:
    North Carolina
    But few are correct
    If the switch doesn’t short the circuit the light will never come on.
    Yes

    The yes answer left just what you are describing here

    Below is what the NEC describes as a fault.
    110.10 Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics.
    The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor(s) permitted in 250.118. Listed equipment applied in accordance with their listing shall be considered to meet the requirements of this section.

    Now going back to that car battery, if I asked you to short out the battery how would you accomplish this? Could the same thing be accomplished by installing a conductor with a switch and simply closing the switch?

    How do we discharge a capacitor? In many cases in industrial establishments this is done by using a switch with a current limiting resistor in series across the capacitor.

    460.6 Discharge of Stored Energy.
    Capacitors shall be provided with a means of discharging stored energy.
    (A) Time of Discharge. The residual voltage of a capacitor shall be reduced to 50 volts, nominal, or less within 1 minute after the capacitor is disconnected from the source of supply.
    (B) Means of Discharge. The discharge circuit shall be either permanently connected to the terminals of the capacitor or capacitor bank or provided with automatic means of connecting it to the terminals of the capacitor bank on removal of voltage from the line.
  19. bluebinky

    bluebinky Member

    Messages:
    406
    Location:
    Santa Clara, CA
    JW, I agree that closing a switch connected to wires across a car battery would cause a short. However, turning on the headlights by closing that switch would not -- just like connecting the terminals of a battery with a piece of wire would cause a short whereas the 2/0 or so wire going to the starter is not considered to be a short. Anyway, our disagreement is pretty small, and we're both too old and stubborn to change. I concede that your usage is "valid", just slightly different than what I was taught. Maybe I'm stuck in the past and need to get out more...

    I think you answered the OPs question in that it was probably not the switch itself, unless as DonL interpreted, the problem was really an open. Too bad he didn't stick around.
  20. Murphy625

    Murphy625 Member

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    149
    Location:
    Michigan
    The term short is always used to describe an unintended electrical pathway. In the overwhelming majority of its use, the term describes a malfunction in which the current finds a less resistive path to ground potential than what was intended. While much rarer, the term could also describe the unintended pathway between two conductors of the same electrical potential.

    Per the battery and switch argument, the closing of a switch is never described as a short because a switch is designed and intended to be closed. That is just called a "closed" circuit. (remember, the term short is always used to describe an unintended pathway that creates a short(er) route)

    One could change the argument perspective and say that a "Closed circuit" is the opposite of an "Open circuit" and that a "short circuit" has no opposite "long circuit" description. Its a silly argument but would seem to create a marriage between the terms "Short" and "Closed" even though the two are used to describe two different intentions.

    Once again, if you're closing a switch that allows current to flow to ground, its not a short.. its just a closed circuit.
    Replacing the light bulb with a fuse only changes the circuit resistance to such a low value that the flow of current becomes too high for the fuse to handle. If you re-routed the wire that connects the switch to the fuse and ran it through Chicago, then Denver, and then back to Chicago, the fuse would probably not blow at all since enough resistance has now been added to slow the current flow. (basic ohms law).
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