A 75kVA transformer is being installed in an old existing multi-story building. I am trying to figure the best way to establish the ground on the secondary side of the transformer. There is no building steel (all concrete building), we are unable to use the water pipe, we are three levels up and the path to the main electrical room is almost unattainable. Do I have any other options? Can I connect the ground to the ground bus bar of the distribution board feeding the transformer? If so, do I need to run a seperate conduit?
Transformer: Establishing ground on secondary side
- Thread starter Hop
- Start date
- Status
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Sounds as though you'll need to pipe down to where the water pipe enters the building, IMO.
fc
Senior Member
- Location
- New Jersey
You say a water pipe is not available on that floor? If there is a water pipe then maybe 250.52 (A) exception can help you out if not george is right you will have to go down.
And if your going to do that you may want to make provision for a tap on the GEC for the 2nd floor.
And if your going to do that you may want to make provision for a tap on the GEC for the 2nd floor.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Here is my answer to the duplicate post that you had on the NEC forum:
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The transformer secondary must be bonded to the metal water piping system. There is an exception that allows bonding to the structural metal of the bulding when it is bonded to the water pipe and is a grounding electode. Since you have no bonded steel in the vicinity of the seperately derived system you would need to bond directly to the metal water piping system. Look at 250.104(D):
Quote:
250.104(D) Separately Derived Systems. Metal water piping systems and structural metal that is interconnected to form a building frame shall be bonded to separately derived systems in accordance with (D)(1) through (D)(3).
(1) Metal Water Piping System(s). The grounded conductor of each separately derived system shall be bonded to the nearest available point of the metal water piping system(s) in the area served by each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.66 based on the largest ungrounded conductor of the separately derived system.
Exception No. 1: A separate bonding jumper to the metal water piping system shall not be required where the metal water piping system is used as the grounding electrode for the separately derived system.
Exception No. 2: A separate water piping bonding jumper shall not be required where the metal frame of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the metal water piping in the area served by the separately derived system.
(2) Structural Metal. Where exposed structural metal that is interconnected to form the building frame exists in the area served by the separately derived system, it shall be bonded to the grounded conductor of each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.66 based on the largest ungrounded conductor of the separately derived system.
Exception No. 1: A separate bonding jumper to the building structural metal shall not be required where the metal frame of a building or structure is used as the grounding electrode for the separately derived system.
Exception No. 2: A separate bonding jumper to the building structural metal shall not be required where the water piping of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the building structural metal in the area served by the separately derived system.
(3) Common Grounding Electrode Conductor. Where a common grounding electrode conductor is installed for multiple separately derived systems as permitted by 250.30(A)(4), and exposed structural metal that is interconnected to form the building frame or interior metal piping exists in the area served by the separately derived system, the metal piping and the structural metal member shall be bonded to the common grounding electrode conductor.
Exception: A separate bonding jumper from each derived system to metal water piping and to structural metal members shall not be required where the metal water piping and the structural metal members in the area served by the separately derived system are bonded to the common grounding electrode conductor.
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The transformer secondary must be bonded to the metal water piping system. There is an exception that allows bonding to the structural metal of the bulding when it is bonded to the water pipe and is a grounding electode. Since you have no bonded steel in the vicinity of the seperately derived system you would need to bond directly to the metal water piping system. Look at 250.104(D):
Quote:
250.104(D) Separately Derived Systems. Metal water piping systems and structural metal that is interconnected to form a building frame shall be bonded to separately derived systems in accordance with (D)(1) through (D)(3).
(1) Metal Water Piping System(s). The grounded conductor of each separately derived system shall be bonded to the nearest available point of the metal water piping system(s) in the area served by each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.66 based on the largest ungrounded conductor of the separately derived system.
Exception No. 1: A separate bonding jumper to the metal water piping system shall not be required where the metal water piping system is used as the grounding electrode for the separately derived system.
Exception No. 2: A separate water piping bonding jumper shall not be required where the metal frame of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the metal water piping in the area served by the separately derived system.
(2) Structural Metal. Where exposed structural metal that is interconnected to form the building frame exists in the area served by the separately derived system, it shall be bonded to the grounded conductor of each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.66 based on the largest ungrounded conductor of the separately derived system.
Exception No. 1: A separate bonding jumper to the building structural metal shall not be required where the metal frame of a building or structure is used as the grounding electrode for the separately derived system.
Exception No. 2: A separate bonding jumper to the building structural metal shall not be required where the water piping of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the building structural metal in the area served by the separately derived system.
(3) Common Grounding Electrode Conductor. Where a common grounding electrode conductor is installed for multiple separately derived systems as permitted by 250.30(A)(4), and exposed structural metal that is interconnected to form the building frame or interior metal piping exists in the area served by the separately derived system, the metal piping and the structural metal member shall be bonded to the common grounding electrode conductor.
Exception: A separate bonding jumper from each derived system to metal water piping and to structural metal members shall not be required where the metal water piping and the structural metal members in the area served by the separately derived system are bonded to the common grounding electrode conductor.
A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
Just for my information, if this scenario was on the ground floor, a ground rod could be driven to ground the secondary, right???
Tom, A seperate ground rod would not bond systems together.The requirement to bond systems together is due to the fact that this is a seperately derived system,Seperated by the coils of the xfrmr.If this system was'nt bonded to the existing systems,there would be a difference of potential and just driving a rod will not surfice by itself.
Rick
Rick
- Location
- Illinois
- Occupation
- retired electrician
Rick,
250.58 does not specify what is needed to bond electrodes together.
In my opinion, the primary EGC provides the required bonding between the SDS grounding electrode system and the building grounding electrode system.
Don
250.58 does not specify what is needed to bond electrodes together.
In my opinion, the primary EGC provides the required bonding between the SDS grounding electrode system and the building grounding electrode system.
Don
- Location
- Illinois
- Occupation
- retired electrician
Paul,
Don
The code requires that the SDS have a grounding electrode.
Don
bphgravity
Senior Member
- Location
- Florida
What section of the code requires the grounding electrode for the SDS be bonded to the grounding electrode for the service. 250.58 really applies?
- Location
- Illinois
- Occupation
- retired electrician
Bryan,
Don
Why wouldn't it apply? The SDS is an AC system that is connected to a grounding electrode. I don't think this is ever a real issue as this section does not specify the type of bonding. The required primary EGC will provide a bond back to the service grounding electrode. It might not be a direct path, but there will be a path.
Don
RUWired said:
250.30(A)7 requires this to be as near as practical.Also if the primary EGC to the SDS was used to bond,then it would'nt be continuous if it was fed from a sub panel .I don't think it would be of proper size as well.A typical 75kva primary ground @ 480 would be a #8,The secondary GEC @ 208 would be a # 4.
Rick
- Location
- Illinois
- Occupation
- retired electrician
Rick,
Don
What code section says that the bond between the building grounding electrode and the SDS grounding electrode must be continuous? What section specifies the size of the conductor that is used to bond these two grounding electrode systems together?
Don
pierre
Senior Member
- Location
- Westchester County, New York
I am not sure where 250.58 comes into play here???
250.64(C) requires an GEC to be continuous and unbroken.
250.30(7) requires the connection to the metal water pipe, or steel, if available.
250.30(5) Requires one to follow 250.64(A), (B), (C), and (E).
This would pretty much require one to install a GEC back to the metal water pipe within 5 ft of entrance.
250.64(C) requires an GEC to be continuous and unbroken.
250.30(7) requires the connection to the metal water pipe, or steel, if available.
250.30(5) Requires one to follow 250.64(A), (B), (C), and (E).
This would pretty much require one to install a GEC back to the metal water pipe within 5 ft of entrance.
- Location
- Illinois
- Occupation
- retired electrician
Pierre,
250.30(A)(5) requires that the SDS grounding electrode "shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system". If a grounding electrode is really needed for a SDS, then it makes no sense to connect to a remote grounding electrode. It appears to me that the there is somewhat of a conflict between the first and second sentences of this section. The first saying that the grounding electrode "shall be as near as practicable" and the second telling me to use the closest of the water pipe or building steel no matter how remote they are from the SDS.
Don
250.30(A)(5) requires that the SDS grounding electrode "shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system". If a grounding electrode is really needed for a SDS, then it makes no sense to connect to a remote grounding electrode. It appears to me that the there is somewhat of a conflict between the first and second sentences of this section. The first saying that the grounding electrode "shall be as near as practicable" and the second telling me to use the closest of the water pipe or building steel no matter how remote they are from the SDS.
Don
Don. Your calling this a bond wire, i am calling this a GEC per 250.30(A)3. If this was used to bond all the grounding electrodes together per 250.53(C) then no it does'nt need to be continuous.The path for me saying that it needs to be continuous is 250.30(A)7 exception #1 because in this case the electrodes are not in the area, so any of the other electrodes listed in 250.52 shall be used.And the conductor to this shall be 250.64(C) (continuous).And this GEC shall be sized per 250.66.
Rick
Rick
- Location
- Illinois
- Occupation
- retired electrician
Rick,
All of my comments are based on installing a grounding electrode at the SDS. The connection between this local grounding electrode and the buidling grounding electrode is a bonding conductor.
Don
All of my comments are based on installing a grounding electrode at the SDS. The connection between this local grounding electrode and the buidling grounding electrode is a bonding conductor.
Don
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