Results 1 to 6 of 6

Thread: Thinking in traffic

  1. #1
    Gold Member
    Join Date
    Jun 2020
    Location
    Fourways
    Posts
    776
    Thanks
    121
    Thanked 36 Times in 35 Posts

    Thinking in traffic

    Hello

    So was sitting in traffic as one does in laodshedding and had a thought...

    The neutral conductor shall at least be the same CSA as the phase conductor.

    Now the above is great for single phase but then with 3 phase we now have 3 current carrying conductors.

    So let's say all wired in 16mm cable the phases and Neutral. On a 60Amp triple pole CB.

    But if each phase had to pull 50Amps that neutral won't be able to carry 150Amps !

    So is this just due to domestic homes and diversity being used or am I missing something ?

    I get it there where 3 single phase machine always running at 50Amps then the Neutral is sized accordingly i.e for 150Amps (well more but for sake of conversation and maths let's stick with easy numbers)



    Sent from my CPH2197 using Tapatalk

  2. #2
    Platinum Member
    Join Date
    Jun 2017
    Location
    Port Elizabeth
    Posts
    1,401
    Thanks
    39
    Thanked 331 Times in 278 Posts
    If each phase drew 50 amps it would be balanced and the neutral would not carry any current , in the perfect world without losses, harmonics etc .

    We work on a star point config , so a vector system - if phases are imbalanced then the neutral will carry the difference to earth

  3. #3
    Gold Member
    Join Date
    Jun 2020
    Location
    Fourways
    Posts
    776
    Thanks
    121
    Thanked 36 Times in 35 Posts
    Yes sorry I meant that it's not a 3 phase load, rather 3 seperate single phase loads.

    So red phase does geyser
    Yellow does oven
    Blue does microwave

    Above is just examples as they don't pull 50A but it's just some theory im working with.

    I guess if you say a 3 phase supply but the

    Red cottage A.
    yellow cottage B.
    Blue cottage C.

    Then if they all use the ovens and kettle at the same time that Neutral would have to carry all that but it's normally always sizes same as the phase

    Sent from my CPH2197 using Tapatalk

  4. #4
    Platinum Member
    Join Date
    Jun 2017
    Location
    Port Elizabeth
    Posts
    1,401
    Thanks
    39
    Thanked 331 Times in 278 Posts
    Quote Originally Posted by Dylboy View Post
    Yes sorry I meant that it's not a 3 phase load, rather 3 seperate single phase loads.

    So red phase does geyser
    Yellow does oven
    Blue does microwave

    Above is just examples as they don't pull 50A but it's just some theory im working with.

    I guess if you say a 3 phase supply but the

    Red cottage A.
    yellow cottage B.
    Blue cottage C.

    Then if they all use the ovens and kettle at the same time that Neutral would have to carry all that but it's normally always sizes same as the phase

    Sent from my CPH2197 using Tapatalk
    Same story - There is still a point were all 3 come together

  5. #5
    Gold Member
    Join Date
    Jun 2020
    Location
    Fourways
    Posts
    776
    Thanks
    121
    Thanked 36 Times in 35 Posts
    Ahhh interesting... What about the time it takes for the Neautral to take to earth would it not carry more current than the cable ?


    I rememeber something I think from Kirchof about a node having no voltage or amps, can't remember but that may then be why there is no excess current in the Neautral or all the phases because they come to a node...

    Sent from my CPH2197 using Tapatalk

  6. #6
    Gold Member
    Join Date
    Jun 2020
    Location
    Fourways
    Posts
    776
    Thanks
    121
    Thanked 36 Times in 35 Posts
    Thinking now they also 120degrees out so the Neautral will carry let's say the Red phase first then Yellow then the Blue, so it does not actually add up on the Neautral.



    Sent from my CPH2197 using Tapatalk

Similar Threads

  1. Thinking a bit...
    By Dylboy in forum Electrical Contracting Industry Forum
    Replies: 25
    Last Post: 24-Aug-22, 10:35 PM
  2. Thinking outside the box.
    By Derlyn in forum General Chat Forum
    Replies: 0
    Last Post: 16-Jul-22, 09:32 PM
  3. Is there anyone else thinking its August?
    By Debbiedle in forum General Chat Forum
    Replies: 1
    Last Post: 19-Mar-08, 08:26 AM

Did you like this article? Share it with your favourite social network.

Did you like this article? Share it with your favourite social network.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •