On jobs where a building or structure.
Ground rod resistance requirement.
This requirement clarifies that the supplemental electrode system must be.
The nec and ul require a ground rod to be at least 8 feet in length.
If this additional electrode is another ground rod it must be driven at least 6 away.
For instance if a ground rod is driven into a very rocky and dry area it may not conduct electricity into the ground well.
Find out why the national electrical code 25 ohms or less rule may have less to do with power quality than you think.
This does not create the best ground but it meets the bare minimum of the code.
In practice for a residential structure most electricians place two ground rods and call it done.
Ideally a ground should be zero ohms of resistance but.
In some instances ground rods can be installed in areas where the earth has a lot of resistance.
The nfpa and ieee recommend a ground resistance value of 5 ohms or less while the nec has stated to make sure that system impedance to ground is less than 5 ohms specified in nec 50 56.
The length of a ground rod plays a much bigger role in its final ground resistance measurement and it goes without saying that it takes longer to drive a longer ground rod.
If this is the case for your ground rod the best solution is to drive a different rod into a different location.
With this method the resistance of two electrodes in a series is measured by connecting the p1 and c1 terminals to the ground electrode under test.
There is no requirement to retest the resistance.
In areas where driving ground rods may be impractical the two point method can be used.
Ground rod current source lightning average current 30 000 amps.
Nearly all electricians and electrical inspectors are familiar with the national electrical code requirement in sec.
Grounding and bonding transient voltages and currents at data port or cable connections voltage difference.
250 54 which requires the resistance to ground of a single made electrode e g ground rod to be 25 ohms or less.
I do not know of an equivalent requirement in the british standards.
In areas where codes require two ground rods because of high electrical resistance in the soil the rods must be spaced at least 6 feet apart and interconnected by a buried jumper wire.
