bphgravity
Senior Member
- Location
- Florida
This is a thought experiment.
I have a 300-ampere service with 350-kcmil service entrance conductors. Table 250.166 requires a 1/0 copper grounding electrode conductor.
If I have no electrodes present, I can drive a ground rod. A mximum #6 AWG is required. It is understood that conductor sizes larger than #6 to a single rod or rods is ineffective due to total surface area of a ground rod its high contact resistance to the soil.
If a concrete-encased electrode is present, I am only required to install a #4 AWG electrode conductor. But wait... Hasn't it been established that the Ufer ground provides the least overall impedance of all permitted electrodes.
If I have a 10-ft metal frame member in direct contact with the earth or encased in concrete, this electrode would have to be connected with a 1/0? How is this electrode any more effective as compared to the concrete encased electrode? The same for the water pipe, it needs supplementing, yet still requires the full sized electrode. Makes no sense to me.
Any ideas or thoughts on the subject?
I have a 300-ampere service with 350-kcmil service entrance conductors. Table 250.166 requires a 1/0 copper grounding electrode conductor.
If I have no electrodes present, I can drive a ground rod. A mximum #6 AWG is required. It is understood that conductor sizes larger than #6 to a single rod or rods is ineffective due to total surface area of a ground rod its high contact resistance to the soil.
If a concrete-encased electrode is present, I am only required to install a #4 AWG electrode conductor. But wait... Hasn't it been established that the Ufer ground provides the least overall impedance of all permitted electrodes.
If I have a 10-ft metal frame member in direct contact with the earth or encased in concrete, this electrode would have to be connected with a 1/0? How is this electrode any more effective as compared to the concrete encased electrode? The same for the water pipe, it needs supplementing, yet still requires the full sized electrode. Makes no sense to me.
Any ideas or thoughts on the subject?