1. Junior Member
Join Date
Aug 2018
Location
Kansas City , MO
Posts
6
Originally Posted by Ingenieur
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. Senior Member
Join Date
May 2008
Location
London, England
Posts
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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. Senior Member
Join Date
Jun 2003
Location
Hawthorne, New York NEC: 2014
Posts
3,973
Originally Posted by Brafs4411
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?

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.

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

-Hal

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