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....
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....