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Thread: Can a 3way switch short?

  1. #31
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Murphy625 View Post
    You think that two breakers feeding one line wouldn't???

    15 amp breaker + 15 amp breaker feeding 14ga wire = big trouble... (think toaster element)

    Think parallel circuit.

    If that could EVER happen, then the electrician that installed it should lose his or her job.

    Stuff like that can not happen if installed properly.

    And Your "Short" would have to be in the breaker box, or the current for each breaker will not be divided by half, It will depend on the resistance of the wire on the Other "Short".

    Is everyone confused yet ?

    We all need to stay on the same page.
    Last edited by DonL; 09-03-2013 at 12:29 PM.
    Theory only works perfect in a vacuum.

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  2. #32
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Murphy625 View Post
    You think that two breakers feeding one line wouldn't???

    15 amp breaker + 15 amp breaker feeding 14ga wire = big trouble... (think toaster element)

    Think parallel circuit.
    two 15 amp breakers feeding one 14 gauge wire that would mean that they would be on the same leg in the panel would equal 15 amps protecting one 14 gauge wire

  3. #33
    DIY Senior Member Murphy625's Avatar
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    Quote Originally Posted by DonL View Post
    If that could EVER happen, then the electrician that installed it should lose his or her job.
    Stuff like that can not happen if installed properly.
    You would be surprised at the stuff that happens inside industrial factories. I've seen conduits crushed by high-low forks, boxes damaged when someone drops a 200lb bearing housing, wires melted by someone welding too close, etc etc. No one wants to take responsibility and things go unreported.
    Residential wiring is so simple I would generally agree with you, however, even then, I've seen mice chew through insulation and people put nails through wires.

    And Your "Short" would have to be in the breaker box, or the current for each breaker will not be divided by half, It will depend on the resistance of the wire on the Other "Short".
    Yup.. that is correct. That said, the difference in the lengths of the wires would have to be significant to create enough of a resistance to have any real world effect.

  4. #34
    DIY Senior Member Murphy625's Avatar
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    Quote Originally Posted by jwelectric View Post
    two 15 amp breakers feeding one 14 gauge wire that would mean that they would be on the same leg in the panel would equal 15 amps protecting one 14 gauge wire
    I'm speechless...

  5. #35
    Electrical Contractor/Instructor jwelectric's Avatar
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    Wouldn’t your two wires also add up?

  6. #36
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Murphy625 View Post
    You would be surprised at the stuff that happens inside industrial factories. I've seen conduits crushed by high-low forks, boxes damaged when someone drops a 200lb bearing housing, wires melted by someone welding too close, etc etc. No one wants to take responsibility and things go unreported.
    Residential wiring is so simple I would generally agree with you, however, even then, I've seen mice chew through insulation and people put nails through wires.


    Yup.. that is correct. That said, the difference in the lengths of the wires would have to be significant to create enough of a resistance to have any real world effect.

    I have worked in industrial factories.

    I do not recall any 14 Gauge wire used in them.

    You are mixing apples with oranges. I like them both.

    I thought we were talking residential, not 3 phase stuff.


    My Bad.
    Theory only works perfect in a vacuum.

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  7. #37
    Sprinkler Guy Wet_Boots's Avatar
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    Quote Originally Posted by Murphy625 View Post
    Did you just call the load an abnormal condition per the definition you posted?



    Two circuit breakers feeding a single conductor will create a situation that could involve the fire department, the insurance company, the hospital, and possibly the morgue.
    I lived in a house that had a wiring fault that was unresolved for years, involving the entire second floor being on a single 15 amp breaker. This was due to a mistaken connection somewhere in the second floor wiring that joined two separate 15 amp circuits together. The two breakers were positioned in the box so as to provide a dead short in the event that they were both on, and being good breakers, that never happened.

  8. #38
    DIY Senior Member Murphy625's Avatar
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    Quote Originally Posted by jwelectric View Post
    Wouldn’t your two wires also add up?
    I'm not sure what you're asking with that question... But, the fact is that two 15 amp breakers feeding a single conductor would theoretically be capable of delivering 30 amps. IE: 15 x 2 = 30. The 14ga wire would eventually melt and catch fire if that happened.

  9. #39
    DIY Senior Member Murphy625's Avatar
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    Quote Originally Posted by DonL View Post
    I have worked in industrial factories.
    I do not recall any 14 Gauge wire used in them.
    You are mixing apples with oranges. I like them both.
    I thought we were talking residential, not 3 phase stuff.
    My Bad.
    I've done my share of single phase stuff too... Every 3 phase factory has at least one step-down transformer to feed single phase to the offices and sometimes the lighting.

    Ohms law and all the other stuff doesn't care how many phases there are or where its located...

  10. #40
    DIY Senior Member Murphy625's Avatar
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    Quote Originally Posted by Wet_Boots View Post
    I lived in a house that had a wiring fault that was unresolved for years, involving the entire second floor being on a single 15 amp breaker. This was due to a mistaken connection somewhere in the second floor wiring that joined two separate 15 amp circuits together. The two breakers were positioned in the box so as to provide a dead short in the event that they were both on, and being good breakers, that never happened.
    It sounds like the two breakers were on opposite phases.. You got lucky because your crossed wires showed their ugly head.. had those breakers been on the same phase, you would have never known until you drew 20 amps on a 15 amp conductor...

  11. #41
    DIY Senior Member bluebinky's Avatar
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    Hasn't this died down yet?

    I too have a piece of paper that says how wonderful I am -- BSEE from University of Washington. The funny thing is, I think I forgot more while at the U than I learned. I wired my first light switch when I was 6 years old...

    As JW was busy quoting the NEC, I was Googling for dictionary definitions and reading Wikipedia, etc. After filtering out all the fluff, the one "definition" that stood out said something like "a short bypasses part of a circuit".

    I don't agree that a short is always unintentional -- if you intentionally set a crescent wrench on a car battery that would be a short in my book (don't do that BTW).

    I roomed in a house once that you needed to turn off three breakers to kill anything and everything. Wonder if it's still there.

  12. #42
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Murphy625 View Post
    I'm not sure what you're asking with that question... But, the fact is that two 15 amp breakers feeding a single conductor would theoretically be capable of delivering 30 amps. IE: 15 x 2 = 30. The 14ga wire would eventually melt and catch fire if that happened.
    You said:
    Quote Originally Posted by Murphy625 View Post
    If two different conductors from two different circuit breakers originating from the same phase leg come into contact with each other (lets say via a break in the insulation of both wires running next to each other), what condition would you call that? In such a situation, that condition may go unnoticed for a very long time until special circumstances occurred between the two circuits.
    then somehow you ended up with just one wire.

    I have been doing electrical work since 1966. I have done about everything one can think of from wiring single wide mobile home to water plants at 4160 volts and the one thing I have never seen is what you are describing.

    Yes I know that industrial maintenance men get to see everything but in most cases it is because they install the mess.

    Having done consulting in many plants around my area I too have seen some pretty sloppy work done in the industrial plants. It has been my experience that the reason behind this type of work is the lack of education and supervision. In other words if the boss don't know how can he guide.

  13. #43
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Murphy625 View Post
    I'm not sure what you're asking with that question... But, the fact is that two 15 amp breakers feeding a single conductor would theoretically be capable of delivering 30 amps. IE: 15 x 2 = 30. The 14ga wire would eventually melt and catch fire if that happened.

    Since we are Nitpicking,

    That would depend on the length of the wire.
    Theory only works perfect in a vacuum.

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  14. #44
    DIY Senior Member Murphy625's Avatar
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    Quote Originally Posted by jwelectric View Post
    You said:
    then somehow you ended up with just one wire.
    Imagine 2 breakers feeding 2 wires.. somewhere down the line, the 2 wires contact each other.. Now you basically have a parallel circuit up to the point where the two wires contact.. Further down the line pass the point of contact, you have 2 individual wires again but they are both being feed by the same parallel circuit. Now, lets say one breaker was feeding a bedroom and the other was feeding a bathroom. The bedroom or the bathroom have now effectively become a 30 amp circuit being provided by a 14ga (15amp) wire. Did that clear up what I was trying to say?

    I have been doing electrical work since 1966. I have done about everything one can think of from wiring single wide mobile home to water plants at 4160 volts and the one thing I have never seen is what you are describing.
    One of the other posters in this thread commented he had a house that had this problem happen.. but his breakers were on different phases so they popped immediately. That said, I'm sure there are lots of things you have seen that I have not.. I am not an electrician who pulls wire for a living. I've certainly done my share of it, but its not my normal daily job.

    My daily job is to cruise forums and nik pick at folks like you! LOL

  15. #45
    Electrical Contractor/Instructor jwelectric's Avatar
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    At my ripe old age all I do is sit around trying to remember those things I have forgotten.
    Now let’s see, is it the base times the height or is it the base squared plus the height squared then we have to make a root square…………… no, no, no it is if you have a tree that has square roots then it won’t get very high and you will have to hide the pot in a noose. Yea that’s it and also if you try to borrow money at the bank and they won’t let you sine you have someone to cosine for you. Well let’s not get off on a tangent here.

    I still feel sorry for poor ole Oscar because Oscar had a heap of apples and that is all anyone needs to know to find the sine or the cosine.

    Lots of fine folks think that equals one half but to the wise they will say that is one divided by 2 or that is the reciprocal of 2

    Such nonsense that I once remembered while the young of today can only think about getting horizontal.

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