Announcement

Collapse
No announcement yet.

E

Collapse
This topic is closed.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    E

    Hey does EMF stand for Electro motive force or electro Magnetic force?

    #2
    Re: E

    When used in electrical theory it is usually the abbreviation for electromotive force.

    In the case of this forum's name, I believe it is meant to be electromagnetic field(s)

    Electromagnetic force is one of the four fundamental forces in the universe (gravity, weak, electromagnetic, strong).

    It can also stand for electromotive field and a mess of other things: http://www.acronymfinder.com/af-quer...ct&Acronym=EMF

    Len

    [ February 21, 2003, 11:24 PM: Message edited by: Len_B ]

    Comment


      #3
      Re: E

      EMF (electromagnetic fields) is being used as a quick designation for effects of power frequency magnetic fields which were not supposed to be there as the wiring system was designed. This is usually dealt with as a "power quality" issue, but since it is a relatively new issue and only refers to power line frequencies,(not RF)it has it's own three letters. For better or worse.

      The effect of the undesigned magnetic fields is to induce currents which interfere with sensitive electronic instruments and also to affect living organisms.

      Most of these elevated fields are due to wiring errors (Code violations) and so introduce the additional hazards of overheating and possible shock.

      The errors involve incorrect connections of neutrals which allow neutral current to leave its dedicated circuit and flow on grounding paths as well as on neutrals supplying other circuits. The result is called "net current", whose magnetic field is directly related to the amount of diverted neutral current.

      The required grounding to metal water pipes also produces diversion of neutral from the service entrance conductor to water pipes, which returns to the transformer by way of other service neutrals, thus producing more net current paths. Now we tie into the "stray current" topic.

      Karl Riley
      Karl Riley
      Moderator

      Comment


        #4
        Re: E

        karl:

        This subject is a little above my head, but....

        After reading your post I couldn't help but think of the case where inductive heating takes place between two separate knockouts in a steel box when current passes in only one direction through one of the knockouts, restricted by NEC 300.20(B). This could be caused for example by using a separate 2-wire cable assembly and knockout in a steel box for the travelers between 3-way switches. Is this situation and resulting inductive heating a form of EMF as used by this forum?

        Comment


          #5
          Re: E

          Mike, I don't think it is over your head at all. Yes, the inductive heating you speak of is induced by the magnetic field causing eddy currents in the steel. The magnetic field also spreads out around the box, and so there could be other effects in nearby equipment.
          Since electricity is generated by moving magnetic fields, the topic is actually central to electricity itself. Fortunately when all conductors run together (300-3(b) the magnetic fields cancel almost completely.
          Karl
          Karl Riley
          Moderator

          Comment


            #6
            Re: E

            Karl,
            Do you know of any reference material that will help calculate the effect of this inductive heating? I was wondering how hot a 12 gauge conductor might get when carrying approximately 9 amps of net current. I recently found a piece of machinery that had been mis-wired, resulting in the situation described above.

            Thanks,

            Tim

            Comment


              #7
              Re: E

              Tim, electrical formulas calculating reactance, etc are my weak point. Perhaps someone who knows how to calculate these things will help us out.
              Karl
              Karl Riley
              Moderator

              Comment

              Working...
              X