Hello,

I'm having my foundation replaced here in California, and I'm
wondering about opportunities to improve my ground electrode system
before the concrete is poured. The foundation is engineered and has
alot of rebar, and the foundation contractor has installed a 20 foot
length of copper wire in the foundation. I assume this is tied to the
rebar and will double check.

Is this sufficient? The foundation consists of about 100' of stem
wall with a footing about 3' deep, about 100' of retaining wall with a
footing 6' deep, and a concrete slab of 450 square feet about 4' below
grade. The surrounding soil is clay. I assume that I should insure
that the rebar of the various elements (stem wall, retaining wall and
slab) are electrically connected? Are there any other measures I
should take, like a grounding rod below the slab?

On a related question, if my main panel and my service disconnecting
means are separate, should the grounding electrode system tie in at
one or the other or both?

Thanks,
Wayne

"Wayne Whitney" wrote in message
...
Hello,

I'm having my foundation replaced here in California, and I'm
wondering about opportunities to improve my ground electrode system
before the concrete is poured. The foundation is engineered and has
alot of rebar, and the foundation contractor has installed a 20 foot
length of copper wire in the foundation. I assume this is tied to the
rebar and will double check.

Is this sufficient? The foundation consists of about 100' of stem
wall with a footing about 3' deep, about 100' of retaining wall with a
footing 6' deep, and a concrete slab of 450 square feet about 4' below
grade. The surrounding soil is clay. I assume that I should insure
that the rebar of the various elements (stem wall, retaining wall and
slab) are electrically connected? Are there any other measures I
should take, like a grounding rod below the slab?

On a related question, if my main panel and my service disconnecting
means are separate, should the grounding electrode system tie in at
one or the other or both?

Thanks,
Wayne

The 20 feet of usually #4 bare solid copper is the minimum for a ufer
ground. Used mostly in the western US. I have installed 40' of larger
conductor and gotten minimal improvement. It really depends on the soil
resistivitiy. There are meters that can provide the readings or you could
hire someone to do it for you.
I would suggest to you that you allow the installation as is and then after
the fact drive a ground rod more than 10 feet way from the foundation and
connect that as well to your service. Connect the ground rod with #4 buried
in the ground. Here in AZ your required to use a ufer. On a service change
you must drive 2 ground rods or provide documentation that you have achieved
25 ohms or less. Driving 2 rods is way cheaper than providing the
documentation. Amec makes a cool meter that measures grounds with out
taking them out of service. Check ww grainger about 2k.

If your interested performance grounding starts out at less than 10 ohms and
some specify less than 5.

The electrical service is where the neutral, grounded conductor is
established. A separate ground wire of the proper size should be run from
the service to the panel. Assuming your a typical residential service that
would mean 2 hots a neutral and a ground.

You had better get the electrical inspector to take a look before you pour
concrete otherwise he may not accept the ground as being suitable.

On one of the last buildings I worked on in Los Angeles the masonry
contractor showed up one day with a crew to lay down rebar and to pour
concrete with no advance warning. I had to scramble to get my grounding
electrode conductor attached to the rebar and run it back to where the
service entrance would eventually be. I had no time to get it inspected,
but the building owner had a camera on hand and I took pictures.

Because the electrical inspector knew me and was familiar with my work from
other jobs he approved the ground based on the pictures, but he told me if
it was someone else he would not have accepted the pictures and would have
demanded an additional ground or chop up the concrete.

The connection to the rebar should be made with connectors suitable and
approved for that purpose. I suggest at least a #4 bare copper wire, but if
it was me I would put in at least 40' of #1 with most of the wire in the
dirt and the end attached to the rebar. I'm not sure, but I don't think
clay is an ideal soil for grounding. If so, then the more copper in contact
with the soil the better.

I'm not sure if it is necessary to bond all of your footings, foundation,
and slab together. It would certainly improve your resistance to ground
though, if you did.

The grounding electrode conductor should only be connected at the service
entrance. If installing a subpanel, you would install a grounding conductor
along with your feeders to the subpanel and terminate it separately from the
neutral bar. Do not bond the neutral bar in the subpanel to the grounding
conductor. Install a separate ground bar in the subpanel instead. In your
case you would bring the grounding electrode conductor to the service
disconnect and treat your main panel as though it were a subpanel.


John Grabowski
http://www.mrelectrician.tv




"Wayne Whitney" wrote in message
...
Hello,

I'm having my foundation replaced here in California, and I'm
wondering about opportunities to improve my ground electrode system
before the concrete is poured. The foundation is engineered and has
alot of rebar, and the foundation contractor has installed a 20 foot
length of copper wire in the foundation. I assume this is tied to the
rebar and will double check.

Is this sufficient? The foundation consists of about 100' of stem
wall with a footing about 3' deep, about 100' of retaining wall with a
footing 6' deep, and a concrete slab of 450 square feet about 4' below
grade. The surrounding soil is clay. I assume that I should insure
that the rebar of the various elements (stem wall, retaining wall and
slab) are electrically connected? Are there any other measures I
should take, like a grounding rod below the slab?

On a related question, if my main panel and my service disconnecting
means are separate, should the grounding electrode system tie in at
one or the other or both?

Thanks,
Wayne

"Wayne Whitney" wrote in message
...
I'm having my foundation replaced here in California, and I'm
wondering about opportunities to improve my ground electrode system
before the concrete is poured. The foundation is engineered and has
alot of rebar, and the foundation contractor has installed a 20 foot
length of copper wire in the foundation. I assume this is tied to the
rebar and will double check.

Is this sufficient? The foundation consists of about 100' of stem
wall with a footing about 3' deep, about 100' of retaining wall with a
footing 6' deep, and a concrete slab of 450 square feet about 4' below
grade. The surrounding soil is clay. I assume that I should insure
that the rebar of the various elements (stem wall, retaining wall and
slab) are electrically connected? Are there any other measures I
should take, like a grounding rod below the slab?

On a related question, if my main panel and my service disconnecting
means are separate, should the grounding electrode system tie in at
one or the other or both?

I can't tell if they are trying to make a ground ring, or a concrete encased electrode. You could do
both by planting a #2 bare all around the base perimeter of your foundation (must be at 30" deep for
a ground ring) and clamp it to the rebar at a few places too. Code says that rebar ties done tight
are acceptable bonding from rebar to rebar. With this electrode, you shouldn't need any others. If
you want to put in more that would be OK, but you shouldn't need two rods since the Ufer/ring do not
require a supplemental ground.

Grounding electrode conductor must tie in to your disconnect, meter base, or service conduit/mast.

--
Mark
Kent, WA