ECN Forum Forums General Topics of the Trade General Discussion Area Grounding Question

Technically if the rebar is sticking out of the footing, you can't use it. It is not a "concrete" encased electrode. It is just a piece of rebar. That was what I was told by the state.

Harold:
Yes, they (DCA) are not happy with rebar sticking out of the concrete to attach a #4 to. Reading various posts here, the rebar sticking out is acceptable in some locations!

The reasoning I got was that the rebar would corrode (rust) over time. That's understood, but where is that written??

Cu and Galv rods deteriorate over time.
Cu (metalic) water mains into structures are of unknown/undocumented lengths; deteriorate over time, and are replaced with plastic.

To the best of my knowledge, the above are not 'written' anywhere either.

The turned up rebar is pretty standard here. A piece of copper wire sticking up would never survive the building process. It would be broken off, probably by a copper pirate.

I've got a question along the same lines. I am getting ready to start an addition in December. I went and looked at it yesterday. Where the ground rods are along the wall is going to become footings for a new wall. the meter is ok where it is. Can they dig footers around the rods and I drive the rods all the way in below the footers. Or do I need to run a new ground to new rods or the footer?

I'd say that you really want to create a "Ufer" in the footer. Code or no, it's a MUCH better electrode than any rod.

I agree, Create a Ufer in your new footer and bond that to your existing rods. You can't have too much ground.

If you are doing an addition which requires removing and relocating the existing ground rods, and since it is an existing structure that will remain occupied, do you have to drive a temporary ground rod?

Yes but I would make it a supplemental electrode to whatever system you end up with.

Greg
We had some very interesting debate here in the great white North contemplating a code change for the Canadian Code. The 2012 edition of the CEC has 1 simple rule for grounding. Not smaller than #6. That is it for low voltage AC systems. No ampacity table, no various electrode types for different wire sizes etc. #6 from a 15 amp to a million amps under 750 volt service.
You can actually have way more ground than enough and when we examine the normal purpose of grounding and the normal fault path for OC protection that we discover the ground wire does very little beyond voltage stabilization and a real poor backup for a failed neutral or other bonded return path.
We looked at European rules, US rules and obviously our own rules and found many surprises in ground wire sizing but most of the larger ground wires (bigger than #6) were sized for fault current and not voltage stability. This is true for some NEC and CEC rules but the CEC was by far the most conservative wire size. In the NEC it seems only a UFER needs a bigger wire than #6.
Unlike the NEC we removed resistance and impedance requirements for grounding low voltage (<750 volts) many codes ago. We also treat water pipes a little differently as we may use then as a ground electrode or just bond it and add an artificial electrode. In the city I work we often only required a #6 to bond the water mains which was conductively connected to dozens of services and by far the lowest ground resistance to the supply. We were requiring 2/0 ground wires connected to a couple of 10 foot rods too as this was the electrode. It does not take much math to realize the bond wire was usually the lowest resistance between the ground and bonding yet even in very high faults the #6 was never damaged even in cases where the electrodes had long ago turned to rust. It was just that conflict that forced this issue. since 1 wire was called a bonding wire it could be smaller than the ground wire yet be 1/10 the resistance of the ground wire.
The upshot is fault current returns on the grounded system conductor (neutral) and rules to require such over sized ground wires just no longer made sense.
We did discuss the secondary open neutral condition but when this happens, the ground seldom takes over the role or does so poorly as to be useless anyway.
OK so it is my opinion that you can easily have too much ground but hardly too much grounded circuit conductor. Lightning strikes notwithstanding. Of course that is not low voltage either ;-)

It sounds like you're referring to a #6 bond and not a GEC (Grounding Electrode Conductor), they are entirely different and serve different purposes.