size, typed amount of grounding electrodes?

[ritelec]

hypothetical :

at 1200amp device is placed in a wood building on a cement pad with no water..

where does it state that all that is required is a single ground rod with a #6 cu (with resistance of 25 ohms or less) to ground that service? (like a temp service I would think)

is there or when is there the point when it is required to install rings or concrete encased electrodes...

It blows me away that I could have a 800 amp and over and have a single rod as the grounding electrode.

 

[Cow]

We do a lot of ag services out in the middle of nowhere.

We've done LOTS of big services with nothing more than rods for a grounding electrode.

 

[infinity]

hypothetical :

at 1200amp device is placed in a wood building on a cement pad with no water..

where does it state that all that is required is a single ground rod with a #6 cu (with resistance of 25 ohms or less) to ground that service? (like a temp service I would think)

is there or when is there the point when it is required to install rings or concrete encased electrodes...

It blows me away that I could have a 800 amp and over and have a single rod as the grounding electrode.

Look at 250.24(A). If no electrodes exist you're required to make one, sometimes called a made electrode. A single rod at 25 ohms or less would qualify as a made electrode and nothing else is required.

 

[kwired]

You are overthinking this, two rods (or one with resistance of no more than 25 ohms) is good for 30 amps or 3000 amps applications.

It it not for fault clearing, it is for dissipating transients into the earth, and creating a ground reference in general.

Requirements is in 250 part III. Starts off with 250.50 requiring all electrodes present in 250.52(A)(1) through (A)(7) to be used if present.

If none of those are present then you must add at least one of the electrodes in (A)(4) through (A)(8). Of those, rods are usually the chosen item because they are simple and least expensive.

250.53 requires rod, pipe or plate electrodes to have a supplemental electrode if the resistance is over 25 ohms, but only requires one supplemental electrode even if resistance is still over 25 ohms.

 

[Adamjamma]

OK, I know I am a student in all this stuff. No Expert. But, if your grounding setup which is supplied by the ground rod, gives you a low enough value that the breaker will trip, disconnecting the gear from the electricity, withing a given time and at a given voltage, that is what the government wants. It does not have to make sense from our standpoints, but has to work. I mean, here in the UK, if you have what they call a T-T system, which is what you would possibly have way out in the woods, where there is no ground supplied by the utility, and your ground voltage is too high, which is your Ze value, they allow you to add an RCD to the system to shut the system down when the touch voltage is exceeded... which is supposed to then make the system better as you will not have as many cases of the breaker not operating but a fault occuring, because if a fault occurs, the rcd wills sense the higher touch voltage and trip...

Or at least that is what the articles in the three books I am studying on UK electric codes is telling me.

Hopefully, I will now learn whether I am actually learning something from all this reading, now.

 

[ritelec]

Nice.............. thank you

 

[packersparky]

OK, I know I am a student in all this stuff. No Expert. But, if your grounding setup which is supplied by the ground rod, gives you a low enough value that the breaker will trip, disconnecting the gear from the electricity, withing a given time and at a given voltage, that is what the government wants. It does not have to make sense from our standpoints, but has to work. I mean, here in the UK, if you have what they call a T-T system, which is what you would possibly have way out in the woods, where there is no ground supplied by the utility, and your ground voltage is too high, which is your Ze value, they allow you to add an RCD to the system to shut the system down when the touch voltage is exceeded... which is supposed to then make the system better as you will not have as many cases of the breaker not operating but a fault occuring, because if a fault occurs, the rcd wills sense the higher touch voltage and trip...

Or at least that is what the articles in the three books I am studying on UK electric codes is telling me.

Hopefully, I will now learn whether I am actually learning something from all this reading, now.

A ground rod has nothing to do a breaker tripping. It plays no role in clearing faults. It is mainly for protection from lightning and transient voltages.

 

[kwired]

A ground rod has nothing to do a breaker tripping. It plays no role in clearing faults. It is mainly for protection from lightning and transient voltages.

Be careful with the "P" word. A ground rod is not a lightning protection system.

It's presence may be beneficial in some ways during a lightning event, but it won't prevent lightning events nor is it any guarantee that there won't be any damages during a lightning event.

 

[Adamjamma]

A ground rod has nothing to do a breaker tripping. It plays no role in clearing faults. It is mainly for protection from lightning and transient voltages.

actually, if it is deep enough it lowers the fault voltage... or Ze... if you cannot get it deep enough, extra ground rods bonded to eachother at a certain distance apart can help drop the voltages as well. Bonding is what helps keep the ground rods from introducing more problems into your residence or business due to nearby lightning strikes as well as helping clear faults a bit easier. But, ground rods do not get rid of lightning problems any more than surge protectors protect your home totally from lightning problems. A direct hit on your home is probably gonna do damage no matter what you have done to protect your home. But, proper bonding and grounding can protect your home from lightning that hits a tree two blocks away from your home.

you want the best, lowest ground values possible so that if a fault occurs in an electrical installation, sufficient current will flow to operate the fuse or circuit breaker protecting the faulty circuit within a predetermined time. The objective is to make sure that the circuit is disconnected fast enough to prevent overheating and possibly a fire.

 

[infinity]

you want the best, lowest ground values possible so that if a fault occurs in an electrical installation, sufficient current will flow to operate the fuse or circuit breaker protecting the faulty circuit within a predetermined time. The objective is to make sure that the circuit is disconnected fast enough to prevent overheating and possibly a fire.

Ground rods and electrodes in general don't have much to do with fault clearing.

 

[packersparky]

actually, if it is deep enough it lowers the fault voltage... or Ze... if you cannot get it deep enough, extra ground rods bonded to eachother at a certain distance apart can help drop the voltages as well.

I can install two ground rods connected to the grounded conductor with a 6 AWG wire and it is a compliant grounding electrode system. The resistance to ground could be 120 ohms and it would still be compliant. It would also not clear any faults. Only one amp of current would flow on a 120 volt fault and not trip a 15 or 20 amp breaker. The code only states that where a single ground rod is used, the resistance to ground must be 25 ohms or lower. Where other electrodes are used, there is no minimum resistance to ground requirement.

 

[Tony S]

actually, if it is deep enough it lowers the fault voltage... or Ze... if you cannot get it deep enough, extra ground rods bonded to eachother at a certain distance apart can help drop the voltages as well. Bonding is what helps keep the ground rods from introducing more problems into your residence or business due to nearby lightning strikes as well as helping clear faults a bit easier. But, ground rods do not get rid of lightning problems any more than surge protectors protect your home totally from lightning problems. A direct hit on your home is probably gonna do damage no matter what you have done to protect your home. But, proper bonding and grounding can protect your home from lightning that hits a tree two blocks away from your home.

you want the best, lowest ground values possible so that if a fault occurs in an electrical installation, sufficient current will flow to operate the fuse or circuit breaker protecting the faulty circuit within a predetermined time. The objective is to make sure that the circuit is disconnected fast enough to prevent overheating and possibly a fire.

You have to understand the difference between UK and US practices. The US is almost always PME, the UK has a ridiculous mix of TT, PME, TN-S, TN-C-S.

https://www.spenergynetworks.co.uk/userfiles/file/EART-01-002.pdf

 

[Adamjamma]

Actually, from what I was taught, most of USA and the Caribbean use a variation of the TN-C-S system, differing in that the UK has only one phase enter the home, on one voltage, on a two wire system for TT or TN-S or a three wire for TN-C-S and then the ground is pulled from right before the meter at the home supply point inside the home. This point, in my old home and in my daughters home, has a wire that goes outside to a second ground rod, outside, and has the main earthing terminal. Us people who work on systems are not allowed to touch the supply point but there is a disconnect there for if a meter needs serviced or changed. Then you get the meter, then you go to the single phase consumers unit which at my daughters home is separated into three sections of breakers, two of which are covered by a lead RCD...
My daughters home is a textbook of the TN-C-S system.. fairly low Ze into it.
Homes I have worked on in Jamaica differ only in where the main ground is applied and in the lack of a disconnect before the meter, along with the extra line coming in carrying power. The wires look different but do the same thing... as it is also a TN-C-S system.