Grounding rods and testing

grounding

I'm looking to install a couple of vertical grounding rods for a friend's property in the middle of nowhere (very country – The earth is mostly clay, rocks and sandstone)

From the limited research I've done I believe the grounding rods should be about 2.5 metres deep and 5 metres laterally separated.

My questions are:

  1. Have I got the depths and spacing correct?

  2. How far from the building/foundation should the rods be?

  3. If I'm to hire an auger that can exhume 2.5m depth, what diameter should the auger be? I intend to use a slurry of ground enhancement material <- still not quite sure what this stuff is but I guess it's a good conductor? How many KG's for a 2.5m deep hole of "x" diamater

  4. How can I test the efficacy of the finished job? Looking at ground resistance testers (clamp style) they run in to the hundreds of dollars. Also, do you need two grounding rods driven and connected in order to use these clamp style testers? Do you clamp it on the connecting wire or individual rods? Can the connecting wire be buried or is a that a big no-no?

  5. Is something like this a complete waste of money?
    https://www.ebay.com.au/itm/192390605919
    It seems a lot cheaper than the AUD$500 alternatives, probably for a reason.

  6. Any hot tips for what I assume will be an incredibly laborious task? I'm guessing an auger is a better choice than a jackhammer with a macgyver attachment to drive the rods, only because I'm using the ground enhancement material, otherwise a tighter drive from a jackhammer would yield better conductivity I guess.

I know if I'm asking these questions it means I'm probably ill-equipped to be doing the job but I'm making the best of a bad/dangerous situation. I'm installing CB's, RCD's and grounding on an installation that is effectively just hardwired, online and unprotected from ground faults. I figure it's a step in the right direction that simply won't happen if I don't step in. It's a case of a friend thinking his electrical "just works" but he doesn't understand the need for further protection. I hope you guys (and gals) understand where I'm coming from. Many thanks.

Best Answer

This is what the generic "National Electrical Code" calls the Grounding Electrode System. It is USA-published but widely used, and widely subject to the sincerest form of flattery. My answer conforms with this Code

1) 2.5M depth is fine. 5m separation is fine, but more is better. On the other hand, copper wires aren't free so I understand if you don't put them on opposite corners. By using two rods, you are exempt from the need to test the conductance.

2) It's not critical to be close to the building. More important is to be far enough away not to strike its foundation or nick utilities. Closer to the building is somewhat better insofar as protecting the ground wires. You don't want to be on the far side of the property since you want to equipotential bond to the dirt near your house, on the off chance there is a significant voltage gradient across your property.

3) It's not a telephone pole. You don't need to auger it. Lots of people have found inventive ways to drive them. Code doesn't care how you drive it.

  • Often, a fence post driver and some patience will suffice.

  • Here's a guy working in clayish soil who does it tool-less, he adds a small amount of water to churn the dirt in the hole into mud. Works for him.

  • Some people connect a garden hose to a pipe to drive the hole hydraulically. That's kind of nice because it's less likely to damage to any utilities you might hit. A few people say this leaves excessive voids around the rod; I don't believe it. The ground does not like having voids in it, and they'll silt up after a few rains. You could accelerate this process.

4) 5) NEC rules say you only need to test if you are on one ground rod. If you use two ground rods, you are exempt from needing to test/prove the rods. Professionally around here, most installers just install two and don't look back. Simply because testing is so laborious and expensive.

All rods need to have a ground wire going back to the panel. The wire must be continuous without splices. It must be copper. It can be direct buried. I'm not sure if you can daisy chain from one ground rod to the next, but that creates a single point of failure, so I would not.

If you're that worried about it, install three.

6) Don't overthink it or assume it's laborious. Read up (i.e. watch youtube) on how others do it. It's not a highly technical project, you are sticking a copper rod in the ground. Success is when the copper rod is in the ground. Acceptance testing is "there are two rods in the ground".

Ground rods do several things for you.

  • return natural electricity (ESD and lightning) to their source, which is earth.
  • keep your electrical conductors within 250V of earth, which is useful if there is transformer miswiring or leakage that might pull it up to thousands of volts.
  • assure that you are not likely to be bitten getting in or out of the tub
  • help RCDs by providing an easier fault path

Here's what they do not do:

  • they do not return human-generated electricity to source. Quite often in the North American 3-phase system, people will wire an outbuilding and go "Hey, don't need a neutral, just drive a ground rod" -- nuh-uh. Dirt doesn't conduct electricity well enough.
  • they do not make RCDs work. RCDs don't use ground. They observe only current on hot and neutral, and want to see that current be equal. RCDs are a great option if you don't have grounding, so if there are circuits in the building that are ungrounded, slapping an RCD on them is your best bet.
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