My 25-Ohm Obsession

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bphgravity

Senior Member
Location
Florida
There are better things in life to be obsessed with, and even better things in the code itself to be obsessed with, but I can't seem to get past this 25-ohm issue. But in the spirit of discovery and understanding, I continue to look for the source of the magical number...

The first code to contain the 25-ohm section was the 1918 edition. (Thank you John Minick) Before yesterday, I knew the 25-ohm requirement found its way into the code before the 1925 edition, but after the 1909 edition. Also in the 1918 edition, the first allowance for pipe electrodes became code. The original requirement permitted a minimum of a 1-in pipe with no less than 4-ft? of surface to exterior soil.

A lot of people assume the 25-ohm requirement has something to do with rod electrodes, however the 25-ohm pre-dates ground rods by two code editions. Grounds rods don't show up in the code until 1923 and aren't very popular until the 30's.

The story continues....
 

bphgravity

Senior Member
Location
Florida
No, but from the discussion I had with John Minick of NEMA yesterday, it appears that the concern was with creative methods that were considered when installing pipe electrodes. In order to obtain the 4-ft? of surface area using 1-in pipe, the pipe would have to be 12-ft long.

It was understood that some might choose to cut the pipe into sections (2-6ft, 3-4ft, ect) and drive them individually. The overall shallow depth of multiple electrodes would have greater resistance than that of a single 12-ft pipe driven vertically into the earth.

This lead to the 25-ohm requirement though it still doesn't clearly indicate why 25-ohms.

(If anyone out there happens to own a copy of the 1918 NEC and would like to sell it to me - I have a blank check waiting here with your name on it!)
 

joe tedesco

Senior Member
Old Codes

Old Codes

Call the NFPA Library in Quincy, MA at 1-617-770-3000, they will help you with copies of text from older codes.

I believe NFPA has some old code books in stock, last time I checked they had as far back as 1978.

I have an original Grounding report dated from 1949 that may add to this question, and if you search for articles by Creighton Schwan, who wrote for NECA he had a few articles covering this subject.

I will look at my old electrical books and will research this question when I get home.

May God Bless Creighton, he passed away in December 2006.
 

brian john

Senior Member
Location
Leesburg, VA
Why I am not HAPPY

Why I am not HAPPY

George take a look at this photo and see if you can guess what is missing. I am a nice guy with an open door policy, and many employees borrow my books BUT some books are not to leave the office...So far no one has stepped up.

IMGP0259.jpg
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
brian john said:
George take a look at this photo and see if you can guess what is missing.
I can.

From the 2002 NEC: "This 2002 edition supersedes all other previous editions, supplements, and printings dated 1897, 1899, 1901, 1903, 1904, 1905, 1907, 1909, 1911, 1913, 1915, 1918, 1920, 1923, 1925, 1926, 1928, 1930, 1931, 1933, 1935, 1937, 1940, 1942, 1943, 1947, 1949, 1951, 1953, 1954, 1955, 1956, 1957, 1958, 1959, 1962, 1965, 1968, 1971, 1975, 1978, 1981, 1984, 1987, 1990, 1993, 1996, and 1999."

I'd say you're missing 1918, 1920, 1923, 1926, 1928, 1931, and 1933, on the assumption you had everything betwixt 1915 and 1935 at one time.
 

brian john

Senior Member
Location
Leesburg, VA
I'd say you're missing 1918, 1920, 1923, 1926, 1928, 1931, and 1933, on the assumption you had everything betwixt 1915 and 1935 at one time.


I am missing a lot but the one in question is 1918. I have books borrowed all the time but these are off limits (I thought). The earliest I have are 1915, 1918 (somewhere) 1930, 1935, 1937, 1940, 1947, 1951-2005, I am missing 1954 and 1955 in that time frame.
 

JohnJ0906

Senior Member
Location
Baltimore, MD
Brian, may I recomend that you use care storing and handling these? The WORST thing for old paper is the touch of a human hand (oils,salt, etc) There are also special plastic sleives for storing archival materials such as these. Treat them like the treasures they are!

edit to add: Brian I sent you a PM about the above.
 
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tom baker

First Chief Moderator
Staff member
Brian:
There can't be very many 1918 NECs, there were not that many printed to begin with.
I was at Mike Holts office a few years back and he has all the NECs back to 1923 or so.
 

bphgravity

Senior Member
Location
Florida
Has anyone ever come across one of the "national" electrical codes dating to before 1897? As I understand it, there were at least 5 nationally recognized yet conflicting electrical codes up to 1895.
 

celtic

Senior Member
Location
NJ
I have copy of the 1899 NEC ...to big to "attach" here (zip limit is 39.1 kb, file is 219 kb)
 
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