The biggest problem is finding a good earth ground to use as a reference.
If you have copper water pripe feeding the house or if you have a drilled
well, you can probably be sure of a good earth ground. You use an ohmeter
between your box ground and an actual ground. The resistance should be as
close to zero as your meter can read. The higher the resistance, the more
problems you can run into. Your box ground can start to float above zero
I miss the good old days of copper tubing and metal pipe. If you had a 100
foot run of metal pipe going out to a drilled well with 60 feet of casing,
you were pretty darn sure of a good ground. Even having 30 or 40 feet of
copper tubing going out to the water main made a pretty sure round. Now
with polybutelyne and other plastics in the system, it is harder to FIND a
good ground to use as a test.
I am not sure what the NEC requires anymore but the 2 places I built had 2
10 foot ground rounds driven 18" below grade and tied to the box with good
dbchamber at hotmail spam dot com
Remove the spam to reach me
Click to see the full signature.