Announcement

Collapse
No announcement yet.

Disconnection time 120 volts vs 150 volts

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Disconnection time 120 volts vs 150 volts


    Is there any real danger in using a 0.8 seconds as disconnection time for 150 volts line to ground? Or would a sweet spot at 0.7 seconds work? Call me cheap but I don't want to use 0.4 seconds unless I really have to.





    #2
    1 second will work from here.

    What are you removing power from? Is there a current level and time at 150 volts?

    I know it’s all above my pay scale, but I’m curious what you are attempting to do.
    Tom
    TBLO

    Comment


      #3
      Originally posted by ptonsparky View Post
      1 second will work from here.
      I like your thinking

      What are you removing power from? Is there a current level and time at 150 volts?

      I know it’s all above my pay scale, but I’m curious what you are attempting to do.
      15, 20 and 30 amp branch circuits. At 120 volts to ground the breaker is required to trip at 0.8 seconds or under. At 150 volts to ground 0.4 seconds or under. Sounds like a lot simply going from single phase to three phase.


      And don't sell yourself short


      Attached Files

      Comment


        #4
        The time is dependent on the resistance (length) of the 14, 12 and #10 cu.

        Comment


          #5
          I can recall an old farmhouse way out , with a barn wired off of it, to yet another barn in the back 40....

          One could arc something all day long, w/out the ocpd opening @ the main house

          ~RJ~

          Comment


            #6
            A LONG time ago I did an absolute Minimum with max VD for a short time project. 240v 3Ph, IIRC. Under a bolted fault that developed at the far end, the voltage would drop out the control but never blew a 60 amp fuse.
            Tom
            TBLO

            Comment


              #7
              Originally posted by mbrooke View Post
              Is there any real danger in using a 0.8 seconds as disconnection time for 150 volts line to ground? Or would a sweet spot at 0.7 seconds work? Call me cheap but I don't want to use 0.4 seconds unless I really have to.




              If you know the short circuit current at 150V, the short circuit rating constant ( K ) of the type of cable, obtainable from cable manufacturers, then you can calculate the area of cable suitable for your requirement. The formula is . Area= (I/K)*√time. Note:The formula applicable upto 5 seconds only.

              Comment


                #8
                Ah! The area as expressed in formula in my previous post is in Sq.mm.

                Comment


                  #9
                  Originally posted by Sahib View Post
                  Ah! The area as expressed in formula in my previous post is in Sq.mm.
                  Sahib, this is what I'm looking for! I have the mm2. Is this enough?

                  Comment


                    #10
                    Originally posted by romex jockey View Post
                    I can recall an old farmhouse way out , with a barn wired off of it, to yet another barn in the back 40....

                    One could arc something all day long, w/out the ocpd opening @ the main house

                    ~RJ~


                    Indeed what I'm trying to avoid. 60 standing volts on the grounding system might be an issue to anyone with low skin conductivity and standing in mud.

                    Comment


                      #11
                      Originally posted by ptonsparky View Post
                      A LONG time ago I did an absolute Minimum with max VD for a short time project. 240v 3Ph, IIRC. Under a bolted fault that developed at the far end, the voltage would drop out the control but never blew a 60 amp fuse.
                      Yup! You see what I'm trying to avoid (trying to accomplish)

                      So how do I go about the math?

                      Comment


                        #12
                        Originally posted by mbrooke View Post

                        Yup! You see what I'm trying to avoid (trying to accomplish)

                        So how do I go about the math?
                        Perhaps this would help:

                        http://www.electrical-installation.o...ircuit_current

                        http://www.electrical-installation.o...uit_conditions

                        Comment


                          #13
                          Thank you- I will look at your links and ask questions after I eat.

                          Comment


                            #14
                            Originally posted by mbrooke View Post

                            Sahib, this is what I'm looking for! I have the mm2. Is this enough?
                            Enough for what?

                            Comment


                              #15
                              Originally posted by Sahib View Post

                              Enough for what?
                              For the area of the cable.

                              Do you do loop impedance in your Country?

                              Comment

                              Working...
                              X