Transformer Grounding

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A large manufacturing property.
There was an existing delta-delta transformer, that was just replaced with another delta-delta transformer.
The transformer is just outside, but is supplying loads inside of the building. The reason for its location outside, is the lack of room for installation inside.
As per 250.30(7), the grounding should be steel or water within 5 feet of the water entrance.
The installer did not install the GEC for the transformer to either the steel or the water, he used ground rods.

Would this satisfy A(7) and exceptions?

P.S. the premises wiring is not grounded to the water in the building, I do not know where it grounded.
The heavy loads in this building are all delta, 3-phase, 3-wire.
 

quogueelectric

Senior Member
Location
new york
A large manufacturing property.
There was an existing delta-delta transformer, that was just replaced with another delta-delta transformer.
The transformer is just outside, but is supplying loads inside of the building. The reason for its location outside, is the lack of room for installation inside.
As per 250.30(7), the grounding should be steel or water within 5 feet of the water entrance.
The installer did not install the GEC for the transformer to either the steel or the water, he used ground rods.

Would this satisfy A(7) and exceptions?

P.S. the premises wiring is not grounded to the water in the building, I do not know where it grounded.
The heavy loads in this building are all delta, 3-phase, 3-wire.

I say no if there is a copper water main it must be used and groundrods secondary.
 

Smart $

Esteemed Member
Location
Ohio
You are leaving out some pertinent information:
  • Service or SDS transformer?
  • Grounded or ungrounded secondary system?
  • If a grounded system, is there a system bonding jumper and GEC connected at the secondary disconnect?
  • If an ungrounded system, is there a grounding conductor which bonds the transformer frame/enclosure to the balance of electrical equipment?
 
You are leaving out some pertinent information:
  • Service or SDS transformer?
  • Grounded or ungrounded secondary system?
  • If a grounded system, is there a system bonding jumper and GEC connected at the secondary disconnect?
  • If an ungrounded system, is there a grounding conductor which bonds the transformer frame/enclosure to the balance of electrical equipment?


Good questions

1. This is an SDS. The service (I am taking a stab at this), is 480Y/277.

2 & 3. The SDS is not grounded, and there is a poor attempt made at grounding the metallic parts.


I am not the inspector of this job, as a matter of fact, this is an area that requires no license, even though 2 experienced companies did work on this mess. I know from the one who brought me in that neither of them have ever worked on a delta-delta, non-grounded system before.
I am pretty sure that no officials of any kind have been in this facility for a long time.
 

pete m.

Senior Member
Location
Ohio
It would seem that to meet exception 1 to 250.30(A)(7) it would have to be determined that the electrodes specified by 250.30(A)(7) are "not available".

That would be the question to answer in my mind.

Pete
 
It would seem that to meet exception 1 to 250.30(A)(7) it would have to be determined that the electrodes specified by 250.30(A)(7) are "not available".

That would be the question to answer in my mind.

Pete


Pete the water pipe electrode is definitely available. I am curious how others than myself may address the particular situation as I have described.
 

pete m.

Senior Member
Location
Ohio
Pete the water pipe electrode is definitely available. I am curious how others than myself may address the particular situation as I have described.

Given that bit of information I see no way that they can use exception 1 to 250.30(A)(7). The ground rods that have already been installed could obviously remain but a connection to the water line is required IMHO.

Pete
 

Smart $

Esteemed Member
Location
Ohio
Good questions

1. This is an SDS. The service (I am taking a stab at this), is 480Y/277.

2 & 3. The SDS is not grounded, and there is a poor attempt made at grounding the metallic parts.

Hmmm... I'm not sure if we are on the same page.

First, by your judgement the secondary of this transformer is an SDS... the latter "S" standing for "system". The service configuration has no bearing on this System. If the secondary is ungrounded, meaning it has no grounded conductor, or no grounded secondary terminal, then it is an ungrounded system and 250.30(B) would apply, which says (1) the size of the GEC is per 250.66 and permits it to be connected anywhere from source to disconnect and (2) also requires the GEC to be in compliance with 250.30(A)(7).

One difference is there will be no System Bonding Jumper. The other is the transformer, being electrical equipment associated with this SDS, is required to be bonded, but there is no grounded conductor or terminal in the transformer. So if the GEC is connected at the disconnect, an EGC/EBJ must be run and connected to the transformer frame/enclosure. Not being a service transformer, an outside ground rod(s) at or near the transformer is not required, nor can such serve as a substitute for the EGC/EBJ.

To answer your original question, a GEC connection to only one of the two electrodes mentioned in 250.30(A)(7) is required, provided either is avaialble. The likely connection point will be at the disconnect.
 
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Hmmm... I'm not sure if we are on the same page.

First, by your judgement the secondary of this transformer is an SDS... the latter "S" standing for "system". The service configuration has no bearing on this System. If the secondary is ungrounded, meaning it has no grounded conductor, or no grounded secondary terminal, then it is an ungrounded system and 250.30(B) would apply, which says (1) the size of the GEC is per 250.66 and permits it to be connected anywhere from source to disconnect and (2) also requires the GEC to be in compliance with 250.30(A)(7).

One difference is there will be no System Bonding Jumper. The other is the transformer, being electrical equipment associated with this SDS, is required to be bonded, but there is no grounded conductor or terminal in the transformer. So if the GEC is connected at the disconnect, an EGC/EBJ must be run and connected to the transformer frame/enclosure. Not being a service transformer, an outside ground rod(s) at or near the transformer is not required, nor can such serve as a substitute for the EGC/EBJ.

To answer your original question, a GEC connection to only one of the two electrodes mentioned in 250.30(A)(7) is required, provided either is avaialble. The likely connection point will be at the disconnect.


Yes, this is an ungrounded SDS. 3-phase conductors and an EGC installed from the transformer secondary to the first means of disconnect.


This is what I was looking to hear from others. I was curious if others agreed that although the transformer is just outside the building, it still requires a connection to the water electrode (there is no steel electrode).

Thanks
 

Smart $

Esteemed Member
Location
Ohio
... it still requires a connection to the water electrode (there is no steel electrode).
Yes... but, I have questions before I can agree completely in the sense that this SDS needs a GEC run directly to the water electrode.

Is the service run to this same building/structure?
Is the service GES connected to the water electrode?
Does this SDS have a GEC connected to the service GES?

If yes to all three questions, and assuming other coincidental requirements are met, I'm of the opinion the SDS is grounded properly. See 250.50 and 250.58.

An example is a grounding conductor is run with primary to and through transformer to the secondary disconnect. Of course this conductor has to meet the 250.66 size requirement the entire way in addition to irreversible connections if spliced/tapped.

It would be rather obvious violation if there were no GEC at all connected to the water electrode ;)
 
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skeshesh

Senior Member
Location
Los Angeles, Ca
Interesting

Interesting

I pretty much think that you need to comply with 250.30(A)(7). One thing though is from my understanding the point is to keep the grounding as equipotential as possible, but if the premise wiring is not grounded to the piping then that doesn't really make a difference right? so I don't know what would be the technical purpose of doing this, other than code compliance, since you have a grounding rod. And also a quick question: why dont you corner ground the secondary? From what I understand its been shown to reduce arc flash incidents (I guess continuous operation is absolutely essential?)
 
Yes... but, I have questions before I can agree completely in the sense that this SDS needs a GEC run directly to the water electrode.

Is the service run to this same building/structure?
Is the service GES connected to the water electrode?
Does this SDS have a GEC connected to the service GES?

If yes to all three questions, and assuming other coincidental requirements are met, I'm of the opinion the SDS is grounded properly. See 250.50 and 250.58.

An example is a grounding conductor is run with primary to and through transformer to the secondary disconnect. Of course this conductor has to meet the 250.66 size requirement the entire way in addition to irreversible connections if spliced/tapped.

It would be rather obvious violation if there were no GEC at all connected to the water electrode ;)


Yes to question #1, No to questions 2&3.
I cannot tell how the existing 480V service is grounded, as I cannot see inside the enclosure, and there is no connection to the water where it enters the building.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
My 'lil brain has become fuddled..... I don't deal with may situations where the SDS is "outside" the building. 99% of my buildings are "service" supplied by POCO. In terms of grounded systems (POCO supplied) , 250.24(A)(2) would allow us to have a ground rod at the transformer, and the grounded conductor brought to the service and grounding electrodes. connected there. In a ungrounded POCO supplied system it appears that
250.24(E) requires that the electrode system be connected at a point from the service lateral (or overhead) to the service. POCO would be responsible for their transformer bonding.
Where the transformer is not POCO, but the "service" is a point ahead of that transformer, it appears we have to reply solely on 250.30.
On an ungrounded system, when the transformer is located outside the building, could we not have grounding electrodes there and bond the transformer to those per 250.30(B)(1) and consider that a structure ?? Then bond the building electrodes back to the building disconnect per 250.32 ?
This seems like it would mirror what is done with a POCO supplied building service.
 

Smart $

Esteemed Member
Location
Ohio
...and consider that a structure ??
While it may meet the definition, I think calling a transformer a structure is absurd. Regardless, I don't see how it would change much. You'd still have to have a GES at the building served as it would then fall under "additional building or structure" requirements, and an EGC/EBJ between transformer and building equipment would still have to be run. So calling the transformer a structure seems to require more grounding electrodes than it not being a structure.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
250.32 (B) doesn't mention installing a grounding conductor between the two structures on an ungrounded system.
I'm just trying to get it clear in my head why, on a POCO service, the transformer only needs to have a ground rod at the transformer, but if it's not a service transformer it needs to be connected to the structure electrodes.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Am I alone in that the NEC definition of "Service" (by referencing utility" and "Premises Wiring" causes confusion on systems where the customer owns and controls pad transformers, etc.
It seems the requirements to bond to "service equipment" is complicated when the point of connection to utility service is 2 miles away from the building in question.
It doesn't occur often in my area, and when it does I tend to treat the individual building as if the supply was utility. This may not be "proper" and I would appreciate input from engineers/inspectors who see this routinely.
 

Smart $

Esteemed Member
Location
Ohio
250.32 (B) doesn't mention installing a grounding conductor between the two structures on an ungrounded system.
I'm just trying to get it clear in my head why, on a POCO service, the transformer only needs to have a ground rod at the transformer, but if it's not a service transformer it needs to be connected to the structure electrodes.
Refer to 250.32(C) and (D), especially (D)(2)
 
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