Results 1 to 10 of 10

Thread: Three phase / Single phase

  1. #1
    Gold Member Martinco's Avatar
    Join Date
    Oct 2008
    Location
    Rustenburg
    Posts
    927
    Thanks
    175
    Thanked 136 Times in 108 Posts

    Three phase / Single phase

    I guess the gurus should be able to answer my question.

    In SA we have 380 volt 3 phase supply to e.g. a factory. From phase to neutral we have 220/230 volt.
    Why then in USA is the supply 220 volt three phase and 110 volt from phase to neutral ?
    I am specifically referring to the difference from 380 to 220 ( 58 % ) and in the case of USA ( 50 % )
    Martin Coetzee
    Supplier of Stainless Steel Band and Buckle and various fastening systems. Steel, Plastic, Galvanized, PET and Poly woven.
    We solve your fastening problems.
    www.straptite.com

    You may never know what results will come from your actions, but if you do nothing, there will be no results... Rudy Malan 05/03/2011

  2. #2
    Full Member
    Join Date
    Apr 2012
    Location
    Vaal Triangle
    Posts
    55
    Thanks
    2
    Thanked 5 Times in 5 Posts
    Whenever electrical designs are done in South Africa for LV systems 400V(3Ø) & 230V(1Ø) are used as the base operating voltage, and not 380V & 220V.

  3. #3
    Suspended
    Join Date
    Oct 2007
    Posts
    2,346
    Thanks
    0
    Thanked 254 Times in 209 Posts
    the limited knowledge i have with usa electrical installations...it works on a similar basis as the generator...they have a 220/110 system because in theory it is safer to have 110volt feeding circuits in a house ...and the 220 volt circuit will only feed the heavier loads...the usa has a very old system.

    a standard generator purchased in sa "can" also be connected in this manner...so when you go camping you can buy camping stuff from the usa and not worry about the voltage issues...provided you get someone to wire the generator in this manner.

  4. #4
    Platinum Member
    Join Date
    Oct 2008
    Location
    SA
    Posts
    1,520
    Thanks
    207
    Thanked 84 Times in 80 Posts
    I cannot remember exactly, but I also think it has to do with the operating frequency of the actual generators in SA vs USA. i.e. SA 50Hz & USA 60Hz if i remember correctly.

    I am sure someone will verify this soon

  5. #5
    Suspended
    Join Date
    Oct 2007
    Posts
    2,346
    Thanks
    0
    Thanked 254 Times in 209 Posts
    you fellas are too sharp on a sunday morning...you are 100 % correct the frequency in the usa is 60 hz and sa the frequency 50 hz

  6. #6
    Gold Member Martinco's Avatar
    Join Date
    Oct 2008
    Location
    Rustenburg
    Posts
    927
    Thanks
    175
    Thanked 136 Times in 108 Posts
    Ok, but I still do not understand why the difference from 400/380 to 230 and in the case of USA 220 to 110.

    Surely the frequency does not influence the voltage generated, provided the windings/lamination core are designed for the specific frequency.

    Looking at how the center tap of a 3 phase alternator/motor is determined, I cannot understand how a different "formula" can be used for the two different systems.
    Martin Coetzee
    Supplier of Stainless Steel Band and Buckle and various fastening systems. Steel, Plastic, Galvanized, PET and Poly woven.
    We solve your fastening problems.
    www.straptite.com

    You may never know what results will come from your actions, but if you do nothing, there will be no results... Rudy Malan 05/03/2011

  7. #7
    Email problem
    Join Date
    Sep 2010
    Location
    cape town
    Posts
    308
    Thanks
    3
    Thanked 43 Times in 37 Posts
    380/1.732 (sq.rootof3) = 220
    220/1.732 = 127 volts not sure why its a bit higher.

  8. #8
    Email problem
    Join Date
    Sep 2010
    Location
    cape town
    Posts
    308
    Thanks
    3
    Thanked 43 Times in 37 Posts
    i think its actually 110/208 which will work out correctly.

  9. #9
    Bronze Member mikilianis's Avatar
    Join Date
    Dec 2008
    Location
    Cape Town South Africa
    Posts
    125
    Thanks
    164
    Thanked 8 Times in 7 Posts
    Hi guys a shot in the dark could it be economics I mean why do the mines operate on 660Volts 3 phase the higher the voltage the less the current the thinner the conducters

  10. #10
    Diamond Member AndyD's Avatar
    Join Date
    Jan 2010
    Location
    Cape Town
    Posts
    4,923
    Thanks
    576
    Thanked 934 Times in 755 Posts
    All the voltages being discussed are just nominal values and are rounded up, down and any other which way plus there's large allowable tolerances as well. The actual formula is as Bergie stated. There's also a difference of up to 10% between 'supply voltages' and 'equipment running voltages' because of voltdrop across the supply system cabling.
    _______________________________________________

    _______________________________________________

Similar Threads

  1. 3 phase metering
    By murdock in forum Electrical Contracting Industry Forum
    Replies: 5
    Last Post: 11-May-19, 07:41 PM
  2. 3 Phase motor foward/reverse with cam switch
    By superspark in forum Electrical Contracting Industry Forum
    Replies: 3
    Last Post: 05-Dec-11, 10:55 AM
  3. 3 Phase or 1 Phase.
    By mikilianis in forum Electrical Contracting Industry Forum
    Replies: 8
    Last Post: 10-Nov-10, 07:40 AM
  4. [Question] Phase rotation and PSC
    By Master Electrician in forum Electrical Contracting Industry Forum
    Replies: 14
    Last Post: 06-Sep-10, 12:25 PM
  5. [Question] Single phase and 3 phase testing course
    By skatingsparks in forum Electrical Contracting Industry Forum
    Replies: 3
    Last Post: 26-Feb-09, 09:14 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
  •