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Grounding rod at the observatory?

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#1 Taylor

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Posted 04 September 2021 - 08:33 PM

Backstory: I have 2 separate contractors bidding on running electrical to my ROR observatory. Keep in mind both are licensed/bonded/insured. 

 

Contractor A stated this in an email in response to my inquiry about a grounding rod "No, you won’t need a grounding rod because Ron is only running individual circuits out there (enough for you to run all your stuff)". 

 

Contractor B stated yes, he is only running one set of wire to the building, will install a 4 circuit break panel, and ground it out there. 

 

Now I'm not an electrician, but Contractor A seems a little crazy to me. 

We get lightning here near Tulsa, OK with our crazy spring thunderstorms. A house less than 1/2 mile away from me burned down due to lightning hitting the peak of the roof and starting a fire in the attic. 

By my thinking, if lightning strikes the observatory (odds are low, due to it being much shorter than surrounding trees and huge houses, but the odds aren't zero) I would much rather the electricity travel back to earth through a ground rod at the building than taking the path back to my house, through the panel, and down the rod at the house. 

 

Thoughts? 

 

Also, do you guys get your local building dept to do inspections? Technically I'm not required to as the building is a "portable" building and is less than 100 square feet, and the electrical only needs to be inspected on something that would be included in the value of the property if its sold. 



#2 Jim45157

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Posted 04 September 2021 - 09:08 PM

but remember its grounded at the main panel to start with  thats why a is saying no ground rod 


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#3 TOMDEY

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Posted 04 September 2021 - 10:24 PM

You could just call the local inspector and ask. Each of my observatories has double grounding stakes and a breaker box. It's perfectly OK to do that and feel safer, even if code doesn't require it! Here's two of them >>>

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#4 Couder

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Posted 04 September 2021 - 10:32 PM

Consider: you can't go wrong adding protection, whether required or not. My lines are grounded at the pole, the house, but I also put a 6' copper ground rod in for each building. (garage, shop(s) Observatory, and yard building.)

 

There are no building codes here whatsoever. Even in town, anybody can open a restaurant with no inspection or anything, as long as you buy a permit. But then I'm not in town. Needless to say, we don't eat in town either.



#5 diceless

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Posted 04 September 2021 - 10:48 PM

The primary purpose of a ground rod is not for lightning protection, it is to reduce the risk of a shock. It does this in two ways, first it will lower the potential voltage difference between ground and the equipment. And the ground provides a way for a short to trip the breaker.

Personally, I would go with the second option as not only it is grounded, it will give you the flexibility to expand your electrical in the future.

#6 GrandadCast

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Posted 04 September 2021 - 10:57 PM

My run was 250 feet, 240 volts, with proper AC panel, ground faults and a ground rod is installed.

 

Jess



#7 Stickman

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Posted 04 September 2021 - 11:17 PM

  I’m retired now, but the last National Electrical Code required a ground rod be driven if you install a sub panel, which is what Contractor B is proposing.
 It sounds like Contractor A is proposing to run multiple circuits to your observatory instead of installing a sub panel.  In this case, you would not need the ground rod.  This method would require all 20 and 30 amp, 120 volt circuits be protected by a GFI breaker. Plus, depending on the distance from your power source, larger wire may be needed to prevent voltage drop (hopefully, the contractor takes this into consideration).  I would note, overall this would be a more expensive installation than Option B.
  A ground rod is not for lightning protection, a separate dedicated system is required.  The ground rod’s function is to provide a path for fault currents and to insure your protective devices (breakers) will operate properly.

  My two cents is Contractor B sounds like he has a better design and concept of how the power should be installed to your observatory.  


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#8 HunterofPhotons

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Posted 05 September 2021 - 11:13 AM

This subject comes up on a regular basis.

As noted in the above posts a grounding rod is not a protection against lightning.

The use of a second grounding rod for an exterior building does not elicit unanimous advice from electricians or regulators.  I would be wary of two different ground potentials in the case with a second grounding rod.  Ground loops should be avoided with delicate electronics.

The most basic way to supply power to an outbuilding is to run a feed of sufficient capacity to a subpanel and separate into the various circuits in the panel.

 

dan k.


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#9 John Fitzgerald

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Posted 05 September 2021 - 11:20 AM

If you run a branch circuit from a panel or other circuit that already has a ground rod at its origin, then you should not put a ground rod at the outbuilding.   Multiple grounds at different locations cause what is known as step potential.   Some locations have multiple ground rods, but they are driven only inches apart, tied together, and used to increase ground contact in dry soils with poor conductivity. 



#10 Stickman

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Posted 05 September 2021 - 02:17 PM

Specific grounding and bonding rules apply to separate buildings or structures supplied by a feeder(s) or branch circuit(s). A grounding electrode is generally required at such buildings or structures, unless the building or structure is supplied by a single branch circuit and meets the requirements in the exception to NEC 250.32(A).  If a sub panel is installed and served by a feeder, a ground rod or other approved grounding electrode is required.  If a branch circuit with approved grounding conductor is used, a ground rod is not required.


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#11 csrlice12

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Posted 05 September 2021 - 02:24 PM

Hook up ectrodes to neck bolts, Open the observatory roof, release the metal kites with wire strings, wait for the free electricity.


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#12 diceless

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Posted 05 September 2021 - 03:50 PM

If you run a branch circuit from a panel or other circuit that already has a ground rod at its origin, then you should not put a ground rod at the outbuilding. Multiple grounds at different locations cause what is known as step potential. Some locations have multiple ground rods, but they are driven only inches apart, tied together, and used to increase ground contact in dry soils with poor conductivity.


The grounding of a sub panel has different rules in different parts of the country. It is best to know what the code is in your area.

#13 Taylor

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Posted 05 September 2021 - 07:36 PM

  I’m retired now, but the last National Electrical Code required a ground rod be driven if you install a sub panel, which is what Contractor B is proposing.
 It sounds like Contractor A is proposing to run multiple circuits to your observatory instead of installing a sub panel.  In this case, you would not need the ground rod.  This method would require all 20 and 30 amp, 120 volt circuits be protected by a GFI breaker. Plus, depending on the distance from your power source, larger wire may be needed to prevent voltage drop (hopefully, the contractor takes this into consideration).  I would note, overall this would be a more expensive installation than Option B.
  A ground rod is not for lightning protection, a separate dedicated system is required.  The ground rod’s function is to provide a path for fault currents and to insure your protective devices (breakers) will operate properly.

  My two cents is Contractor B sounds like he has a better design and concept of how the power should be installed to your observatory.  

 

 

This subject comes up on a regular basis.

As noted in the above posts a grounding rod is not a protection against lightning.

The use of a second grounding rod for an exterior building does not elicit unanimous advice from electricians or regulators.  I would be wary of two different ground potentials in the case with a second grounding rod.  Ground loops should be avoided with delicate electronics.

The most basic way to supply power to an outbuilding is to run a feed of sufficient capacity to a subpanel and separate into the various circuits in the panel.

 

dan k.

 

 

If you run a branch circuit from a panel or other circuit that already has a ground rod at its origin, then you should not put a ground rod at the outbuilding.   Multiple grounds at different locations cause what is known as step potential.   Some locations have multiple ground rods, but they are driven only inches apart, tied together, and used to increase ground contact in dry soils with poor conductivity. 

 

So it sounds like with the electronics that will be in the observatory, a ground rod could potentially be worse. 

 

So if electrician A runs separate wiring runs for 3 separate circuits (yes, he did upgrade the wiring in the quote to account for the voltage drop over the length), that sounds like a lot of big, expensive wire to run through conduit. 

 

Thanks all! I'm learning a lot about from all of your feedback, appreciate it. 



#14 mark77

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Posted 07 September 2021 - 08:03 PM

I would go with B, put in the grounding rod and a circuit box out there, you will be glad you did.

 

When I built my observatory, the building inspector made me put in 2 grounding rods at least 6 feet apart.  I checked the code and that is what it said.

 

I am an electrical engineer and do all of my own electrical work.  Grounding rods are your friend smile.gif



#15 GoFish

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Posted 07 September 2021 - 08:40 PM

FWIW, the electrical inspector here (WI) told me I was required to install 2 ground rods for my detached garage when I install a new subpanel.

 

I didn’t ask, but my understanding is that it is OK (code-wise) without the ground rods now since the garage is served by a single branch circuit from the main house panel.

 

But I need more power than can be provided by the present single 20A branch from the house. So I will be trenching, laying conduit, pulling wires, and installing ground rods. 
 

I am sizing the feed wires for a tolerable voltage drop.  This results in #4 wire for the 150’ run. This, in turn, means I need a 40A breaker in the house panel.

 

The lugs on a 30A breaker, which would have otherwise been fine for the power needs, can’t accept #4 wire. Moral of the story for the OP is “look closely at the details!”



#16 outofdark

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Posted 07 September 2021 - 09:24 PM

At that distance and  guage You should be good for 70A.  I calculated for 240v.

 

 

 

http://www.paigewire...mpWireCalc.aspx

 

 

FWIW, the electrical inspector here (WI) told me I was required to install 2 ground rods for my detached garage when I install a new subpanel.

 

I didn’t ask, but my understanding is that it is OK (code-wise) without the ground rods now since the garage is served by a single branch circuit from the main house panel.

 

But I need more power than can be provided by the present single 20A branch from the house. So I will be trenching, laying conduit, pulling wires, and installing ground rods. 
 

I am sizing the feed wires for a tolerable voltage drop.  This results in #4 wire for the 150’ run. This, in turn, means I need a 40A breaker in the house panel.

 

The lugs on a 30A breaker, which would have otherwise been fine for the power needs, can’t accept #4 wire. Moral of the story for the OP is “look closely at the details!”

 


Edited by outofdark, 07 September 2021 - 09:26 PM.

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#17 rexowner

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Posted 08 September 2021 - 10:18 AM

but remember its grounded at the main panel to start with  thats why a is saying no ground rod 

Wrong.

 

NEC 250.32 calls for a grounding electrode, with an exception for a single branch circuit.


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#18 rexowner

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Posted 08 September 2021 - 10:27 AM

The primary purpose of a ground rod is not for lightning protection, it is to reduce the risk of a shock. It does this in two ways, first it will lower the potential voltage difference between ground and the equipment. And the ground provides a way for a short to trip the breaker.

Personally, I would go with the second option as not only it is grounded, it will give you the flexibility to expand your electrical in the future.

Yes, a grounding electrode is not for lightning protection.

 

Not sure what is meant by "lower the potential voltage difference."  It will help maintain the same voltage potential at

the grounding conductors in both structures.

 

The grounding CONDUCTOR provides a path for fault current (tripping the breaker).  The reality is this fault current will generally travel

via the grounding CONDUCTOR, back to the service where the grounding conductor and grounded conductor are bonded --

it will then travel back over the utility "neutral" as this is a much lower resistance path than just about any ground rod or

other grounding electrode.



#19 rexowner

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Posted 08 September 2021 - 10:33 AM

...

There are no building codes here whatsoever. Even in town, anybody can open a restaurant with no inspection or anything, as long as you buy a permit. But then I'm not in town. Needless to say, we don't eat in town either.

Yes.  Per this map:

https://www.nema.org...doption-map.pdf

your state of Missouri is one of 4 that have not adopted the National Electrical Code state-wide.

 

The OP is in OK, which has adopted the NEC, but it is "also subject to local adoption."   Hopefully

the local officials are sane enough to just adopt the NEC.

 

While a statement like "local codes may differ" is technically true, the overwhelming majority of the US

has adopted some version of the NEC, where Article 250 is enforced.  It is actually extremely

rare that the NEC does not apply.



#20 rexowner

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Posted 08 September 2021 - 10:36 AM

  I’m retired now, but the last National Electrical Code required a ground rod be driven if you install a sub panel, which is what Contractor B is proposing.
 It sounds like Contractor A is proposing to run multiple circuits to your observatory instead of installing a sub panel.  In this case, you would not need the ground rod.  This method would require all 20 and 30 amp, 120 volt circuits be protected by a GFI breaker. Plus, depending on the distance from your power source, larger wire may be needed to prevent voltage drop (hopefully, the contractor takes this into consideration).  I would note, overall this would be a more expensive installation than Option B.
  A ground rod is not for lightning protection, a separate dedicated system is required.  The ground rod’s function is to provide a path for fault currents and to insure your protective devices (breakers) will operate properly.

  My two cents is Contractor B sounds like he has a better design and concept of how the power should be installed to your observatory.  

Despite several likes, your reply is incorrect.  NEC 250.32 clearly allows an exception only for a SINGLE branch circuit,

which could be a MWBC.

 

Once again, the ground rod is not there for the breakers to trip -- the grounding CONDUCTOR is there for that purpose, and

the fault current will flow back through the service to the utility conductors.



#21 rexowner

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Posted 08 September 2021 - 10:40 AM

This subject comes up on a regular basis.

As noted in the above posts a grounding rod is not a protection against lightning.

The use of a second grounding rod for an exterior building does not elicit unanimous advice from electricians or regulators.  I would be wary of two different ground potentials in the case with a second grounding rod.  Ground loops should be avoided with delicate electronics.

The most basic way to supply power to an outbuilding is to run a feed of sufficient capacity to a subpanel and separate into the various circuits in the panel.

 

dan k.

FYI, the reason a second grounding electrode comes up is NEC 250.53(A)(2) which requires a supplemental

electrode for rod, pipe or plate electrodes unless that path to ground is 25 ohms or less.

 

There is no confusion among people who understand the Electrical Code.



#22 rexowner

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Posted 08 September 2021 - 10:43 AM

If you run a branch circuit from a panel or other circuit that already has a ground rod at its origin, then you should not put a ground rod at the outbuilding.   Multiple grounds at different locations cause what is known as step potential.   Some locations have multiple ground rods, but they are driven only inches apart, tied together, and used to increase ground contact in dry soils with poor conductivity. 

Except what you are proposing violates the electrical code.

 

BTW, in general, NEC 250.53(A)(3) requires supplemental electrodes to be not less than 6 feet apart.



#23 rexowner

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Posted 08 September 2021 - 10:45 AM

The grounding of a sub panel has different rules in different parts of the country. It is best to know what the code is in your area.

Unlikely to apply.  See post #19



#24 rexowner

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Posted 08 September 2021 - 10:51 AM

I would go with B, put in the grounding rod and a circuit box out there, you will be glad you did.

 

When I built my observatory, the building inspector made me put in 2 grounding rods at least 6 feet apart.  I checked the code and that is what it said.

 

I am an electrical engineer and do all of my own electrical work.  Grounding rods are your friend smile.gif

I agree.  Short answer is go with B because unless A is talking about a single circuit, A is wrong.

Licensure (of A) does not guarantee competence.  I deal with construction, and there are so

many people, including inspectors, who don't understand code requirements, it's not funny.

 

In the big picture, driving a couple of ground rods is probably not a big deal.

 

HTH :-)



#25 spacemunkee

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Posted 08 September 2021 - 11:09 AM

The grounding of a sub panel has different rules in different parts of the country. It is best to know what the code is in your area.

This is what I don't care for. Electricity is the same no matter where you go, unless I'm missing something..tongue2.gif

And we're talking electricity, so from a safety standpoint, shouldn't the best way be confirmed and adopted across the board, no ifs, ands or buts?

 

As it reads, yes, one branch circuit to a detached structure, no need. Two or more, or sub panel yes. 

 

Do a lot of detached garages and county i live in says no need with a sub as your feed has its dedicated ground back to main panel. County i mostly work in says yes, and must be a rebar, footer, ufer bond, what ever you want to call it(grounded to a 20' peice of rebar in or on the footer poured within wall).

Other inspection outfit up north says take your pick between a ground rod or rebar.

 

And have read arguments either way on the whole potential thing of one grounding point or multiple.

Just does what I told! 




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