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Thread: Voltage drop

  1. #11
    Join Date
    Aug 2018
    Location
    Kansas City , MO
    Posts
    2
    Quote Originally Posted by Ingenieur View Post
    NEC
    DC R 1.2
    AC Z 1.1
    if you use their R and X (steel) ~ 1.2017 or 1.2010 (pvc or alum)

    where did the 1.24 come from?

    Also use quantity of #1 for Chapter 9 table 8...as it is for a single solid conductor....the 7 represents stranded conductors.

  2. #12
    Join Date
    May 2008
    Location
    London, England
    Posts
    752
    Also remember that within living memory, that electricians had to calculate voltage drop BY HAND with pencil and paper, before the advent of cheap electronic calculators, or cell phones incorporating a calculator.
    Such calculations had to be relatively simple and not involve needless significant digits.

    In the UK and I presume elsewhere, many rules of thumb existed to eliminate calculations on small and simple installations.

    "for lighting in a normal size house, no more than a dozen (15 if you are satisfied that some are very low use) lamps per 5 amp 240 volt circuit. 3/.029 cable is fine for any likely circuit in a normal size house"

    "For ring circuits for general purpose power, use 7/.029 cable on a 30 amp fuse. No limit on number of outlets provided that the floor area does not exceed 100 square yards, AND that the total length of cable does not exceed 100 yards."

    Millions of homes were wired thus, without any calculation whatsoever, and a lot still are.

  3. #13
    Join Date
    Jun 2003
    Location
    Hawthorne, New York NEC: 2014
    Posts
    3,754
    Quote Originally Posted by Brafs4411 View Post
    A question from my Mike holt book,
    A 240v,24A,single phase load is located 100 ft from the panel board and is wired with 10AWG. What is the voltage drop of the circuit conductors?

    Answer in book is 5.76V
    1.20 ohms per 1000 foot the calculation result says.
    10awg 1.240 ohms per 1000 ft

    1.240÷1000=.00124
    .00124×200ft=.248
    .248 ×24A=5.952.

    Why does the book round the numbers.
    Where do you see rounding? Because 1.20/1000 is given and you found 1.24 someplace? If you want the correct answer and pass the test you have to use whatever information is given.

    Check your work-

    1.20÷1000=.00120
    .00120×200ft=.240
    .240 ×24A=5.76.

    -Hal

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