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Thread: Common Wire

  1. #1
    Retired tool & Die and Mechanic Giles's Avatar
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    Default Common Wire

    I have heard several definitions of "common wire". I have heard some people refer to the common as the hot and others refer to the neutral as being common.
    What is the definition of common when used in wiring?

  2. #2

    Default

    I am not an electrician but, I define a common wire by what I am connecting to it. I am not sure if this is what you meant.

  3. #3
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Default

    There is typically one place for the term "common" in AC building wiring. It is the odd wire in a 3-way switching scheme. The other two wires are typically called the travelers.

    A neutral is NOT a "common".

    Some HID fixtures use the term "com" in ballast wiring, but this can be a neutral or hot depending on the feed.
    Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.

  4. #4
    In the Trades maintenanceguy's Avatar
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    Default

    nobody calls either of these wires a "common" wire.

    A neutral wire can be "common" to several different circuits in your house and you can run a special circuit called a "multiwire branch circuit" where both halves of the circuit share a neutral but it's not called a "common" wire by anyone I've ever known or worked with.

    A common wire usually refers to control circuits such as the low voltage circuits for a lawn irrigation system that run out to each electrically operated valve. In these arrangements, one common wire loops from valve to valve. Each valve also gets its own power wire to turn the valve on and off.

  5. #5
    Homeowner Thatguy's Avatar
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    Default

    Common (to more than one load).

    I guess it could be said the hot and the neutral are common to all the outlets connected to them.

    The "wiper" terminal in a 3 way switch (a SPDT switch) could be called common because at one time or another it is connected to each of the other two terminals.
    Same with the wiper of a rotary switch.

    http://www.google.com/search?hl=en&q...common&aq=f&oq=

  6. #6

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    That guy,

    I read this in your link, I am sitting here laughing, it reminds me of something, I used to tell my kids, LOL. I love it. I would tell my kids, to " go pick up your room" they would ask why. I would say, "because you are common." One son, came back to me with a dictionary, and read to me the definition of common. He asked me, " am I an unwashed mass?"

    So, a few days went by. I told him, "go pick up your room, ok?" He said, " Why?" I said, " because you are special." An hour later here he comes again with the dictionary, this time I RAN.

    Today he is a teacher.

    Thank you for the wonderful memory! Cookie

    "the common people in those days suffered greatly"; "behavior that branded him as common"; "his square plebeian nose"; "a vulgar and objectionable person"; "the unwashed masses"

  7. #7
    Electrical Contractor/Instructor jwelectric's Avatar
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    Default

    On the back of a three way switch is the word common

    On a 240/208 to 24 volt transformer is a conductor that is labeled common

    Then in nails we have what is called common such as a 16 penny common

    I once wired some apartments and they were called The Commons

    And finally, I am commonly called arrogant.

  8. #8

    Default

    I didn't call you arrogant. I am not rude.
    I was laughing about my son with That Guy. It was a funny, warm, memory and one of the definitions of " common", unwashed masses. LOL. It is something between my son who at the time, was usually an unwashed mass, LOL, AND 5 years old!
    It had nothing to do with you at all.


    http://www.google.com/search?hl=en&q...common&aq=f&oq
    Last edited by Cookie; 12-06-2008 at 03:25 PM.

  9. #9

    Default

    Quote Originally Posted by Thatguy View Post
    Common (to more than one load).

    I guess it could be said the hot and the neutral are common to all the outlets connected to them.

    The "wiper" terminal in a 3 way switch (a SPDT switch) could be called common because at one time or another it is connected to each of the other two terminals.
    Same with the wiper of a rotary switch.

    http://www.google.com/search?hl=en&q...common&aq=f&oq=



    I agree with your post by the way That Guy.

  10. #10
    Homeowner Thatguy's Avatar
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    Default Game theory is a hobby of mine

    http://en.wikipedia.org/wiki/Tragedy_of_the_commons

    This tragedy has no solution that I know of.

  11. #11
    Electrical Contractor/Instructor jwelectric's Avatar
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    Default

    Quote Originally Posted by Cookie View Post
    I didn't call you arrogant. I am not rude.
    Mrs. Cookie
    Didn't mean to imply that you had but my wife on the other hand does quite often.

    It pains my heart to hear of your situation as my wife has been diagnosed with Pulmonary Fibrosis and has a limited time left with us so I do understand just what hope is about.

    Due to other health problems she will not be recommended for any type of implant. She is a very strong woman that has taught me more about life than most will ever get to understand, Thank you Lord for my wife.

    I hope you the best and please know that you will be in our prayers daily.

  12. #12

    Default

    Quote Originally Posted by jwelectric View Post
    Mrs. Cookie
    Didn't mean to imply that you had but my wife on the other hand does quite often.

    It pains my heart to hear of your situation as my wife has been diagnosed with Pulmonary Fibrosis and has a limited time left with us so I do understand just what hope is about.

    Due to other health problems she will not be recommended for any type of implant. She is a very strong woman that has taught me more about life than most will ever get to understand, Thank you Lord for my wife.

    I hope you the best and please know that you will be in our prayers daily.

    Well, you did it again! I don't like Mrs. Cookie. I sound like a restaurant.
    (Sadly, I am no longer a Mrs, I am a widow.)

    I am truly sorry to hear about your wife, I do wish you both the best, and I hope things turn around. Prayer to me is the very strongest power there is on earth. You both will be in my prayers. I know how hard it must be for you, too. It is not easy living with someone who is sick. We get cranky. But, then men are just born cranky.
    Last edited by Cookie; 12-06-2008 at 10:59 PM.

  13. #13

    Default

    I think I like your wife. Tell her I said so, lol.

  14. #14

    Default

    On the back of a three way switch is the word common

    On a 240/208 to 24 volt transformer is a conductor that is labeled common
    There you go. There is the answer you are looking for when you are talking about residential electrical wiring.
    http://www.inspectpa.com/forum/forum.php
    My answers are based mostly on the ICC codes. Advice given is my personal opinion and every person performing work should acquire a permit from his/her jurisdiction and get the work inspected. My opinions are not directions to follow for DIYs or professionals

  15. #15
    Moderator & Master Plumber hj's Avatar
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    Default Common

    As a practical matter, "common" can be whatever you want it to be, since any shared wire would be "common" to the items it served.

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