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Thread: Connecting 2 different wire sizes

  1. #1
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    Connecting 2 different wire sizes

    I have (2) 100 amp, 3ph, 480V outlets installed in floor. From each outlet there is 1" conduit concrete encased running to each it's own junction box. Those 1" conduits can take only 3#3 awg wires. The panelboard from which (2) 100 amp outlets will be powered, it is 400 ft away. Because of the voltage drop I need to go with bigger wire size, in this case its 2/0 and it cannot be installed in 1" conduit. Now here is my question, I want to install 2" conduit and run 3#2/0 in it to the junction box and from there I need to go with 1" conduit and 3#3. Can I connect #3 and #2/0 together? If it's not allowed, what are my other options?

  2. #2
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    Quote Originally Posted by sergiyny View Post
    I have (2) 100 amp, 3ph, 480V outlets installed in floor. From each outlet there is 1" conduit concrete encased running to each it's own junction box. Those 1" conduits can take only 3#3 awg wires. The panelboard from which (2) 100 amp outlets will be powered, it is 400 ft away. Because of the voltage drop I need to go with bigger wire size, in this case its 2/0 and it cannot be installed in 1" conduit. Now here is my question, I want to install 2" conduit and run 3#2/0 in it to the junction box and from there I need to go with 1" conduit and 3#3. Can I connect #3 and #2/0 together? If it's not allowed, what are my other options?
    It is allowed, but you may have a problem finding a crimped butt splice rated for that size difference. Other options include split bolts and Polaris terminals.

  3. #3
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    Quote Originally Posted by GoldDigger View Post
    It is allowed, but you may have a problem finding a crimped butt splice rated for that size difference. Other options include split bolts and Polaris terminals.


    Also see 314.28 for sizing junction box correctly.
    "Electricity is really just organized lightning." George Carlin


    Derek

  4. #4
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    Yes, you can connect 2/0 to #3. Are you running welders from these receptacles?
    Electricians do it until it Hertz!

  5. #5
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    Quote Originally Posted by JFletcher View Post
    Are you running welders from these receptacles?
    Am I gonna look like a moron for asking why this would be a factor?

    Pretty common to have one welder using one of two receptacles, convenient locations.
    "Electricity is really just organized lightning." George Carlin


    Derek

  6. #6
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    You can also use this to splice them:

    https://www.homedepot.com/p/Blackbur...1-10/100190266

    after splicing cover with rubber tape then plastic tape or use shrink tubing.

  7. #7
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    Quote Originally Posted by jumper View Post
    Am I gonna look like a moron for asking why this would be a factor?

    Pretty common to have one welder using one of two receptacles, convenient locations.
    No. The reason I ask is that welders can use OCPD much higher than wire size and that duty cycle would have a fair amount of impact on wire size. In other words, does he have an actual 100A load at the receptacle?. OP asked if he had any other options; using #2 CU (Still can get 3 in a 1" conduit, using conduit as EGC) back to the panel may be viable.

    Using this calculator:

    http://www.encorewire.com/wp-content...tage_Drop.html

    and the values 480V, Copper, 3ph, 400', and 100A, I get #2 wire is needed.

    Southwire's calculator is not working at the moment as it isnt correctly figuring inputted allowable voltage drop. Using the same specs there I get #1 wire, but at 2.15% VD. I dont see why #2 Cu wouldnt work for his application.
    Electricians do it until it Hertz!

  8. #8
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    Ah, got it. Thanks Fletch.
    "Electricity is really just organized lightning." George Carlin


    Derek

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