Grounding Rod *and* Rebar for service grounds?

[boopus]

You may or may not have a good ground. It's hard to saty without seeing it. If that normal looking ground rod is not being used, you may as well hook it up. You can never have too much grounding, and for less than $5 you may have a better ground. Just buy 2 ground clamps and a length of #6 solid copper wire, as long as the distance between the rods, plus another foot or two for connections.. Did a trench 8 inches or more between the rods, put clamps on both rods, attach wires and fill hole. Pretty easy except for the digging. If the ebar is rusty, file it by the clamp, and apply some silicone caulk around your clamp. You should try to run the wire from the panel into your new clamp too.

[Vinnie Murdico]

Hi,

We have a nearly new home in FL (built in 2001) and I noticed recently that our cable TV coax comes into a box on the outside of the garage before coming into the house. I also noticed that in this box, the cable has a grounding block attached to it, but no ground wire. So I bought some #10 copper wire and ran a wire ground wire from the grounding block in the box down to what I thought was the grounding rod where the electrical service and the phone were grounded. But instead it looks more like rebar instead of a "smooth" grounding rod looks. It comes out of the ground at about a

15-30 degree angle off vertical (i.e. almost vertical).

I can see a #4 or #6 bare copper wire (which I assume is the electrical service ground) coming out of the house and clamping to this rebar, as well as following the grounding wire from the phone demarc box to this rod (actually, the phone grounding wire is clamped to the electrical ground wire about 2 inches from where the electrical ground wire clamps to the rebar. I bought a 5/8" grounding clamp, stripped about 2 inches of insulation from my cable TV coax ground wire, and clamped it directly to the rebar with the rest of them.

Then, I noticed about 16 inches away was what looked like a regular grounding rod sticking out of the ground about 2 inches. This rod is smoother and does not appear to be rebar, but more of a regular grounding rod (or at least what I thought a regular grounding rod looked like). Both the rebar and the grounding rod are less than 6 feet from the AC service panel in the garage. I dug down about 6 inches, but couldn't find anything attached to this smooth grounding rod.

So my questions are: (a) Why is everything grounded to the rebar when there's a grounding rod right next to it? (b) Should the rod and the rebar be bonded together somehow? (c) I can't determine if the rebar is part of the foundation rebar or a piece of rebar driven straight down into the ground. Is it ok as the house's ground if it's part of the foundation rebar and not an 8' stake going down into the ground?

Thanks in advance! -- Vinnie

[Art Begun]

It's because everyone working on your house was an idiot.

Sorry for the sarcasm but the same people were working on my house. Example, screened doors installed upside down. Missing flashing, french drain full of concrete (no joke).

The rebar was probably put in by mistake and everyone thought it was the grounding rod before it got super rusty.

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[Ron Hardin]

Measure the (AC) voltage difference before you measure the resistance. If it's not zero, don't measure the resistance. Two ground rods some distance apart typically have a voltage difference between them even if not attached to anything, but especially if one is in use and the other isn't.

[John Gilmer]

Well, with a high input impedance voltmeter (like your typical digital model) it would be unusualy to NOT detect a fraction of a volt difference.

If such things make you nervous, "load" the circuit by putting a 1000 ohm resistor across the DVM input leads for all measurements. The resistor should provide enough "load" to significantly reduce the voltage reading to your comform level. If you have some stray current leakage inside your house, pull the main breaker during your testing.

The 1000 ohm resistor will change your resistance measurements but your expected value should be less that 100 ohms (much less with "good" grounds).

But checking the voltage before measuring resistance is, indeed, a good practice.