I'm Brazilian and I need to ground my house, especially because of some expensive equipment I don't want to use without proper protection.

By "grounding my house" I mean: provide an alternative path for current to flow to, in case of an electrical discharge or if the neutral provided by the power company breaks, for example. Here all power outlets have a third terminal for that purpose, and it's done by driving metal rods into the ground and connecting those terminals to these rods.

The thing is, I live in as small town and all the electricians around seem not to care for appropriately measuring grounding systems appropriately, by using a ground resistance meter. None of them even had one, and when I expressed my concerns about it (even though I'm admittedly a layman) they all dismissed it as something unimportant.

One of them told me ground resistance meters are expensive and that he'd test using a multimeter. If the voltage between ground and phase was the same as the one between phase and neutral, then it was ok.

Other would said he'd test it with a lamp. If the ground and phase could turn the lamp on, the grounding was good.

The other one (one whom I briefly worked with and the one I trust the most) was the only one who had a different attitude. He first asked me what kind of load I'd have on my system, what I planned to have connected. Then he told me I should have a separate electrical system for each of my showers (or other potent devices), each with individual grounding, and then all the least potent equipment could be connected to the main system, with one grounding for them all. But he also said he didn't have a ground resistance meter, but he'd tackle that by having 'three rods 3 to 5 meters away from each other providing the grounding' and that it should suffice.

So I tried looking into some other info in the internet and everything seems conflicting. The one guy who made the most sense for me was an electrician who told it is indispensable to have a proper meter, but that if you're an electrician and don't have one, there are some tests that are somewhat reliable you could make to make sure the grounding is good.

Basically he said one should disconnect all equipment from the outlets in the house, then do the multimeter test I mentioned before. After that, if the voltages were the same between phase/ground and phase/neutral, he'd connect some potent equipment (he used a drill machine) to phase/neutral and measure the current with an amperimeter. After that he's do the same test while connecting it to the phase/ground and see if the current matches. If those matched, the grounding was good.

I'm now left wondering, I absolutely need good grounding in my house, but the way it seems, I will either have to buy the ground meter - and they're expensive, especially considering ill use it only once - myself or go for one those fishy 'solutions' above.

What are your thoughts on it?

  • You have two concerns here: one is "how well is the fault-current path in your house's electrical system connected together to send wayward utility electricity back to the utility?", and the other is "how well is your house's electrical system connected to earth so that it can send wayward natural electricity back to nature?" Also, what sort of sensitive equipment are we talking about here? Computing equipment? Audio gear? Some sort of instrumentation? – ThreePhaseEel May 11 '20 at 0:15
  • My thought is that you should get hold of a competent and qualified electrician - some countries have licensing for a reason. Some of us had to study and pass rating exams so that we could work on and test electrical systems. – Solar Mike May 11 '20 at 4:34

If the utility neutral breaks you're up against the ground (i.e earth, dirt, soil, water, rocks) being a relatively terrible conductor as compared to a metal wire, so the various tests involving testing the ground with a heavy load between hot and ground are highly dubious.

In the USA, the NEC (our local code, presumably not what applies in Brazil) requires either a ground test (time consuming, expensive meter) or two ground rods 8 feet or more apart, minimum. Many places have also implemented code requiring that in new construction the concrete foundation should include a "Ufer" ground or basically have the reinforcing steel tied into the grounding system, which is a far more effective connection to earth ground than ground rods in almost all soil conditions.

As a result, few electricians here bother to own the expensive meter, and most services have two (or more) ground rods 8 (or more) feet apart; Or one foundation ground (concrete encased electrode) and one ground rod.

  • The heavy load between hot and ground is a very good test of the equipment grounding system, it just doesn't do anything to test the grounding electrode system XD – ThreePhaseEel May 11 '20 at 0:27
  • @ThreePhaseEel Sorry, what you mean in this comment. As English is not my native language, I didn't really get all you said. – Ezequiel Barbosa May 11 '20 at 1:19
  • 1
    @EzequielBarbosa -- grounding is really a two-part exercise: you need a grounding electrode system to connect your house's electrical system to the Earth so that errant natural electricity doesn't cause it to float off to some crazy voltage and damage a bunch of wire insulation in the process and you need an equipment grounding system to connect all the appliances and such back to the service bonding point (US electrical is TN, in IEC earthing terms) so that errant utility electricity (say from a faulty appliance) can be returned to the utility, tripping the bad circuit's breaker. – ThreePhaseEel May 11 '20 at 1:25
  • @ThrerPhaseEel I for sure didn't know that and has never seen anyone saying anything about this. TBH the more I research about grounding systems the more it pulls me down. It's so central and yet I can't get a conclusive stance on it without feeling I'd have to hire and electrical engineer to tell me how should I proceed (not nuking your affirmations here. It's just that everyone says something different I'm already becoming confused about it) – Ezequiel Barbosa May 11 '20 at 1:51
  • 2
    @EzequielBarbosa, part of the reason you're getting conflicting answers is that most countries have their own code for how to do this (or not; in some less developed countries). But most all of the codes are good, so if your country doesn't have one, or it doesn't include good grounding provisions you need, your best bet is to pick a code from a similar country (i.e. US if 120V, somewhere in Europe for 240V) and follow that code to the letter -- that way it'll definitely be safe and effective. – Nate S. May 11 '20 at 15:57

Ezequiel, most electricians do not have earth/ ground resistance meters. For example in the U.S. if you drive 2 each 8 foot rods 6’ apart no measurement is required. A single rod must be below 25 ohms but drive a second rod and who cares.

I have a multi point tester and can tell you that I have seen up to 6 each rods driven and the resistance was still in the 30 ohm range, I have driven multi segment rods in the same area 30’ deep, my plant has a single point tester and it’s measurements are very close to my multi point ( single point used where the ground is covered with concrete or asphalt And the multi point won’t work) What good is a tester unless you specify a value Is 25 ohms a good value because the National electric code uses it and quite a few countries adopt the NEC. Well it is not it is two high to do the job of providing a path to trip a circuit breaker of 15 or 20 amps. Infact for a direct fault to ground would require the resistance to be below 6 ohms so for me a low resistance path to protect sensitive equipment would be 1/2 of that or 3 ohms based on us residential voltage of 120v to ground.

This got long but first you need to specify what value you need, there are other ways to measure by injecting voltage at the ground and measuring amperage but this should be done by a qualified electrician as it can be dangerous. Added per OP request;

To expand on the resistance needed to clear a fault to ground it is a ohms law calculation. amps= voltage/ resistance so a resistance above 6 ohms will not be low enough to trip a 20 amp breaker at 120v or 8 ohms for a 15 amp breaker , you can be electrocuted by less than an amp and when combined with water that lowers skin resistance I have read values below 50 ma can be fatal.

The National Electric Code used by most of the U.S. and some other countries requires any receptacle in a bathroom be protected by a ground fault circuit interrupter (GFCI) these are set to trip at 5ma (milli amps) also protection is required at any receptacle within 6’ from a sink or basin You may be able to get a really good ground at 3 ohms or even less and that will clear the breaker but breakers are inverse time devices and at there rated current they may take minutes or hours to trip. This is why the NEC requires the 5 ma ground fault protection. On your side of the pond RCD is common on your main these trip at 30ma fault current but turn everything off so if you have an RCD you do have some protection. You may also have a different voltage you can plug that into the formula but from my examples you can see it may be difficult to get a low resistance ground path it all depends on soil conditions the best grounding electrode is the metal casing for a well, after a well a UFER ground (a grounding system using the metal reenforcement in a buildings foundation) developed in WW2 for grounding in desert conditions where rods just did not provide a low enough resistance I hope this additional information helps , a RCD or GFCI is usually much better protection from getting shocked in my experience as an electrician.

  • Well, you got some interesting information here. Especially when you say that using multiple rods still renders about 30 ohms of resistance, and the part of the 6 ohms needed for a direct fault also interested me. Could you please elaborate on that? – Ezequiel Barbosa May 12 '20 at 0:46
  • By the way, I don't know what resistance do I need. I just know that first I have a 5kw shower. It's installation is currently coupled with one of the dorm rooms's, but I'll make it individual and ground it. There's another of this shower in the other bathroom and it's installation is already independent from the rest of the house. Then there's that dorm room I mentioned, by taking the shower out, it will also remain independent. I'll be using a 650w PC and some home studio equipment there, that's what I want to protect the most, I intend to ground it and install a surge protector there. – Ezequiel Barbosa May 12 '20 at 0:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.