A lot of thinking went into how electrical systems are grounded - and our homes involve a protective earth, AKA equipment grounding conductor - an Ufer ground.
My Oxford Dictionary defines ground as: an electrical connection to the earth.
Typically, and traditionally, grounding in houses has been done outside, with a rod or some system buried into the earth. An electrode would then carry any fault or short outside to it rather than electrifying things inside the house.
If a "hot" (meaning not grounded) fault was instead diverted inside the home to an exposed conductive surface, like a metal fixture or sink, anyone touching it would close the circuit back to the "earthed" supply conductor and receive an electric shock.
The National Electric Code avoids this hazard, calling for a protective earth, or equipment grounding conductor. Doing so avoids any potential electrification of surface conductors inside the home.
Requirements for the rod thickness and length are defined in the 2006 International Residency Code:
- Electrodes of pipe or conduit shall be not smaller than trade size ¾ (metric designator 21) and, where of iron or steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.
- Electrodes of rods of iron or steel shall be at least 5/8 inch (15.9 mm) in diameter. Stainless steel rods less than 5/8 inch (15.9mm) in diameter, nonferrous rods or their equivalent shall be listed and shall be not less than 1⁄2 inch (12.7mm) in diameter.
Then, during WWII, Herbert G. Ufer, a consultant to the US Army, was working on finding a cheap way to ground buildings used for bomb storage, better protecting them from lightening strikes. He discovered that concrete was more conductive than soil. Concrete has a high pH content - it is very base. As such its ions more readily provide an electrical ground than most types of soils. He also found that copper was damaged by the concrete, so he found steel was better to use used instead.
In 1968 the NEC recognized and required this type of grounding connection unless there was other grounding provided in a home, like copper piping or a ground rod. And they called it "Concrete Encased Electrode," or CEE. Poor Mr. Ufer's name and recognition got dropped!
More and more on new construction I am seeing the whole system inside the house. Essentially an Ufer ground system is being used.
In this house there are two 200amp panel boxes. Each is equipped with a large, black conductor, exiting the box at the top and making its way toward a ground.
Combining the two conductors, they continue together to another area of the basement. They travel together to the Ufer ground rod, where they are both attached and secured. They are circled in red.
The supervisor told me the rod is buried 10' deep.
This builder's electrician does something very interesting.
He bends the top of the rod!
I have not seen this technique before this inspection.
Certainly that is safer and to my mind seems a BEST PRACTICE.
My recommendation: the next time you are in new construction with a client, ask the supervisor if they are using the more traditional ground rod outside the house, or the Ufer ground inside. His eyes will open in surprise at your question, and your client will think you really on top of the latest greatest! When they act surprised, just raise your hands and say, "What? Just asking the question..."
Comments(37)