Electrician says corroded ground electrode needs replacing

[redikillowatt]

It's been my observation that the worst corrosion always takes place within the first few inches of the rod entering the soil.

This is often true - when the only corrosion activity is oxidation. Where both moisture (in higher rainfall areas) & oxygen are plentiful.

SOME soils have higher corrosive effects on various metals, because of actual mineral composition.
In areas w/ high rainfall & layered soil types (different compositions), there can be one layer a few ft down that stays moist, while layers above & below don't retain moisture well. I've seen this many times digging deeper holes.

I've seen pictures of driven rod electrodes dug up in areas of diff layered soil types, that are almost rusted through, ONLY at one spot, well below ground level. That's likely due to higher corrosive action of that soil layer & possibly higher moisture content in that layer.

In my area, you'd have to dig up the entire rod to know if there was serious corrosion in one or more spots along entire 8 ft length, esp. on older rods. It'd be easier to put in a new rod, once the upper part shows significant corrosion.

Here's a link to a paper listing just some factors of various soils corrosive activity, where corrosion can occur well below ground level.
http://www.csun.edu/~bavarian/Courses/MSE 531/corrosion_class_notes/Corrosion_Chap_11.doc

 

[weressl]

This is often true - when the only corrosion activity is oxidation. Where both moisture (in higher rainfall areas) & oxygen are plentiful.

SOME soils have higher corrosive effects on various metals, because of actual mineral composition.
In areas w/ high rainfall & layered soil types (different compositions), there can be one layer a few ft down that stays moist, while layers above & below don't retain moisture well. I've seen this many times digging deeper holes.

I've seen pictures of driven rod electrodes dug up in areas of diff layered soil types, that are almost rusted through, ONLY at one spot, well below ground level. That's likely due to higher corrosive action of that soil layer & possibly higher moisture content in that layer.

In my area, you'd have to dig up the entire rod to know if there was serious corrosion in one or more spots along entire 8 ft length, esp. on older rods. It'd be easier to put in a new rod, once the upper part shows significant corrosion.

Here's a link to a paper listing just some factors of various soils corrosive activity, where corrosion can occur well below ground level.
http://www.csun.edu/~bavarian/Courses/MSE 531/corrosion_class_notes/Corrosion_Chap_11.doc

Let's not forget galvanic corrosion or electrochemical corrosion. Galvanic corrosion occuring between two dissimilar metals with the ground moisture acting as the electrolyte, simple electrochemical corrosion is by salts and metals.

 

[petersonra]

On a remodeling addon job, the electrical contractor says the single grounding electrode needs replacing because it has rust at the top where a brass acorn clamp is attached (rod is exposed above grade). It is rusted, but clamp looks good. He also wants to replace the short GEC from panel to driven rod.

Is it necessary to replace a ground electrode because it has rust? For grins, I cleaned a spot on the rod below the brass grounding clamp & shined a spot on outside of brass clamp a bit & also a spot on GEC ( above the ground clamp). Resistivity between clamp & rod, and the GEC (from above clamp) to rod - below clamp - then were each < 1 ohm. Seems to indicate conductivity between both GEC, brass clamp & rod are still good, in spite of corrosion.

Can't say about resistance between such rusty ground rods & earth in a high rainfall area like this. He didn't check that.
The rod & clamp above ground were dry at the time of testing, but it has rained w/in last week.

I've worked on hundreds of older homes w/ similar looking rods & electricians never give them a 2nd look. I wonder if inspectors would require replacing rusty, but otherwise solid driven ground rods or what the actual requirements are for deciding if a driven ground rod needs replacing?

If he is paying you to replace it, I would just do so. Easy money.