Detached new garage build with 60 amp subpanel from main house. Used UF 6/3 all the way. Neutral and equipment ground at the subpanel. Most of the threads discuss putting two grounding rods at the garage but we were told it wasn't necessary with this set up and since the house is already grounded. True or false? If it is necessary, how would we add those?
Grounding rod question
- Thread starter lqchar
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BillK
Well-known member
l,
The only person who can correctly answer the question for you is the person who will be doing the final inspection.
The only person who can correctly answer the question for you is the person who will be doing the final inspection.
sberry
Banned
Many accept 1 rod but I think 2 is the rule regardless of who inspects. 8 ft or so apart and connected with a continuous wire number 8 or better. We use a 6 just because we can and have it.
alfredeneuman
Well-known member
Unless YOU can prove to the inspector (with some very expensive test equipment) the the impedance to ground is 25 ohms or less with 1 rod, then by Code you need to drive an additional rod, and no more rods will be required.
The rods must be at least 6' apart.
The test equipment's cost is the reason why most electricians just choose to drive the 2nd rod as a matter of course.
Of course if you put a UFER (concrete encased electrode) ground in the footing and attach to it, no other electrode would be required.
The rods must be at least 6' apart.
The test equipment's cost is the reason why most electricians just choose to drive the 2nd rod as a matter of course.
Of course if you put a UFER (concrete encased electrode) ground in the footing and attach to it, no other electrode would be required.
This is rural and won't be inspected but we want it to be safe. Too late for a UFER, the garage is finished. Are one or two grounding rods needed for safety? And if so, could someone please explain why the house grounding is insufficient. Thanks so much.
Leaflessshadetree
Well-known member
Distance from the house to the garage might cause enough difference in voltage during an incedent to induce current through the wiring.
Expensive equipment is required to do the testing that would be necessary at your specific location and results can be affected by soil conditions.
Ground rods are easy to install, cheaper than testing and most likely to perform better.
Expensive equipment is required to do the testing that would be necessary at your specific location and results can be affected by soil conditions.
Ground rods are easy to install, cheaper than testing and most likely to perform better.
acer66
Well-known member
OP, where are you located?
aandpdan
Well-known member
Inspected or not, the NEC requires a ground rod for your detached garage. 2 are usually installed so as to not have to deal with the 25 ohm requirement.
sberry
Banned
I am not sure I understand this?
Falcon67
Well-known member
Two is the rule here, unless using a UFER.
toyotadriver
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My electrical utility only requires one ground rod for house service. I installed 2 anyway at the service entrance.
I installed an additional 1 rod per subpanel. Electrical utility didn't require it but it made me feel good.
I installed an additional 1 rod per subpanel. Electrical utility didn't require it but it made me feel good.
Leaflessshadetree
Well-known member
Ground, dirt, rocks etc. has resistance. It's the same reason for shuffling with your feet close together if you find yourself near a downed power line. Basically you are keeping both feet at the same potential. get them too far apart and your legs could be the path of least resistance.
If there is less than 25 Ohms resistance between the buildings then they will be close enough to the same potential that the separate ground is not required.
Ohms law I=V/R.
wyliesdiesels
Well-known member
Make sure that the neutral bus is isolated in the subpanel. U may need a seperate ground bar kit.
If lightning hits your detached structure and there is no rods there, then the lightning has no where to go but down the wires that connect to your house.
EVERY detached structure requires grounding electrodes regardless of what the feeding structure has.
U add 2 rods by connecting them with one continous piece of #6 bare solid cu wire (or u can use #8 cu but that requires conduit) making sure its not subject to damage and connecting it to the ground bar in the subpanel.
Actually the NEC already answers it. The inspector should just be saying what the NEC calls for.
Explained above.
Doesnt matter what the PoCo requires. They arent the authority that regulates inside wiring. The NEC requires 2 if 25 ohms or less of resistance to ground cant be proven.
The NEC still requires grounding electrodes regardless of the potential between buildings.
Luther Grimace
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What is the reason conduit is required for #8 cu but not for #6 bare solid cu wire?
Also to OP I read where you are using UF to feed from the main panel to the sub? Is that in conduit in the house and outside underground or is that not required?
toyotadriver
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Since there are no codes where I live, then we only have to make the power company happy. The power company supplied me with their engineer drawings that specified what had to be done to get service. I exceeded their requirements but they only require 1 ground rod at the service entrance.
sberry
Banned
The rod is there for some step potentials between anything grounded in the building and the earth you are standing on but mainly to shunt lightening strikes, rather it go to earth there vs being carried on the egc back to the first structure.
Power company vs. NEC?
NEC wins. Put another ground rod, it's $10 and some sweat FFS.
R.Anderson
Well-known member
That is where the NEC draws the line for the wire needing protection from getting damaged, #8 has smaller diameter than #6.
R.Anderson
Well-known member
So where do you live? What state?
wyliesdiesels
Well-known member
As to why they chose #8, U would have to look into the code making panels' notes, that came up with that came up with that. Im sure it has to with #8 being smaller diameter and thus easier to break.
Thats illogical and silly. Of course u have codes. Theyre just not enforced.
If u didnt have codes then why do u have #12 on a 20a breaker? Why not put it on a 30a breaker for a general use circuit? Or why are any of the other circuits in your house protected by the correct breaker size?
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toyotadriver
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What is so hard to understand? I could put 14 ga on a 20 amp breaker if I wanted to. Stupid to do so of course but there are no codes where I live. Yes there is a national code but there is NO enforcement so therefore it's a suggestion, not a requirement.
wyliesdiesels
Well-known member
Ok and where did u get that its stupid to put #14 on a 20amp breaker? The NEC table 310.15(b)(16) perhaps???? That would be a code...
Just because its not enforced doesnt mean u dont have codes
R.Anderson
Well-known member
Thank you for the explanation!
rburke65
Well-known member
Obviously he....she.....don't want to tell ya where they live........move on brother.
We were going to use MHF which would have had to switch to a different type of wire once in the house and would have needed conduit. We were told if we used UF 6/3 we could go all the way with no conduit so while it was a bit more expensive, it was much easier.
sberry
Banned
A small ground wire needs physical protection.
53Sparky
Well-known member
One of my best friends is a long time electrical engineer. He always jokes when an inspector asks for extra ground rods that "Ground Rods are the placebo of the electrical industry"
In certain areas here in the Rocky Mountains, the soil so poor that the resistance to ground is so HIGH (edited after WylieDiesels pointed out my mistake) that any conductivity is almost negligible and therefore the ground rod is not helpful.
UFER grounds have made a better solution here.
But to your question, a second ground rod might be required by code in your jurisdiction. If you are asked to do it, it's not worth arguing about it. It should cost you almost no time, $$ or effort.
In certain areas here in the Rocky Mountains, the soil so poor that the resistance to ground is so HIGH (edited after WylieDiesels pointed out my mistake) that any conductivity is almost negligible and therefore the ground rod is not helpful.
UFER grounds have made a better solution here.
But to your question, a second ground rod might be required by code in your jurisdiction. If you are asked to do it, it's not worth arguing about it. It should cost you almost no time, $$ or effort.
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wyliesdiesels
Well-known member
U mean the resistance to ground is high?
It should be the other way around.
If theres poor conductivity the resistance would be high.
53Sparky
Well-known member
right. you're totally right. I swapped the terms in my head. Good catch.