Resistance of Rod

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Dennis Alwon

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I suspect not or at least not much if the grounding electrode conductor stays the same

BTW, welcome to the forum
 

Smart $

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Ohio
If you were to drive a larger rod in the same location as a previously installed smaller rod you'd find it has a lower resistance to ground. How much, I do not know... but I doubt it will be significant.
 

infinity

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Does the size of the rod affect the resistance from the rod to the ground?

I would think that it would make some difference. For example a 1" rod would have 2X the surface area of a 1/2" rod for the same length therefore you would have 2X the amount of metal in contact with the earth.
 
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Dennis Alwon

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I would think that it would make some difference. For example a 1" rod would have 4X the surface area of a 1/2" rod for the same length therefore you would have 4X the amount of metal in contact with the earth.

Yes but isn't the soil resistivity a factor? A larger rod may help but connected to a #8 wire will probably not help much.
 

gar

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Ann Arbor, Michigan
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171003-2356 EDT

Dennis:

In my area an 8 ft rod fully driven in the ground might be as low as 15 ohms to remote earth. #8 copper of any likely length will be substantially below 1 ohm.

What is wrong with either of these is skin resistance at high frequencies. Much better would be the same cross sectional area of copper, but in a thin copper sheet. Lightning is a high frequency currernt.

.
 

Carultch

Senior Member
Location
Massachusetts
Does the size of the rod affect the resistance from the rod to the ground?

A little bit, but not nearly as much as the length. The electrical resistance is as follows, assuming the rod's internal resistance can be neglected:
R = rho*ln(4*L/D)/(2*pi*L)

where:
rho is resistivity of the semi-infinite solid (i.e. soil)
L is the length buried
D is the diameter

Compare the following:
A: 1/2" rod at 8 ft - base case
B: 3/4" rod at 8 ft
C: 1" rod at 8 ft
D: 1/2" rod at 10 ft

Resistance of B is 6.1% less resistance than the base case. 125% more rod material.
Resistance of C is 10.4% less resistance than the base case. 300% more rod material.
Resistance of D is 17.3% less resistance than the base case. 25% more rod material.
 
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