SDS Bonding question

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benaround

Senior Member
Location
Arizona
For the record, I'll agree with pete m. on post #3, as the only compliant

way to answer the OP's question.

crossman, this Forum is great for making the light bulbs come on!!

smart$, we will have to disagree on this, imo, there is no need for the excpt.

if it can be used anytime.
 

crossman

Senior Member
Location
Southeast Texas
Smart $ said:
Interpretation of the defintion is not limited to the one which you have made. As stated previously, please note the use of the word source and originate (or grammatical forms thereof).

A premises wiring system whose power is derived from a source... other than a service. Such systems have no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.

I'm just not seeing it the way you are. Hopefully we can get some comments from other members and their thoughts on the idea.


Concerning my : "Note that these exceptions do not relieve one of the requirements in 250.104(D)."

Smart $ said:
I did not state otherwise. The OP concerns instances where these grounding electrodes are not available in the immediate area.

Sorry about the implication that you stated otherwise. It wasn't intended and I definitely wasn't being rude! I was just pointing out 250.104(D) for the benefit of anyone else who happened to read this thread. And I agree, the OP didn't have building steel or waterpipe.
 

Smart $

Esteemed Member
Location
Ohio
crossman said:
Hopefully we can get some comments from other members and their thoughts on the idea.
Hmm... had an outside-the-box thought.

Is there any code which restricts running a solidly grounded circuit conductor from the primary system to X0 of the transformer?

If not, one could run such a conductor, and thus the xfmr would no longer be an SDS...???!!!
 

Smart $

Esteemed Member
Location
Ohio
automate0042 said:
I am time constrained and cant reference the above to the code. What's the concensus- is this application an SDS?
Is your initial post in this thread an actual installation that you are inquiring about?
automate0042 said:
I dont have much experience w/ SDS systems, but i am curious. If the 480v supply was a grounded B phase (say), and the GEC was routed to the xfmr and connected to case w/ X0, would that change the xmrs SDS status?
 
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RB1

Senior Member
I agree with Benaround. 250.30(A)(3) Exception No. 2 is intended to apply to unit substations or switchboards that contain transformers. In cases like these the separately derived system originates in the same equipment where the service or feeder is grounded. This exception first appeared in the 1999 Code. The language relating to feeders was added to the 2002 Code for multibuilding complexes.
 

RB1

Senior Member
I would also add that Don's proposal was spot on and should have been accepted. Looking at the performance requirements of system grounding found in 250.4(A)(1) you find concerns relating to lightning strikes, line surges, and unintentional contact with higher voltage lines. It seems to me that these concerns are unfounded for systems located inside of a building envelope, especially when that building supplied by a grounded AC service of less than 600-volts.
 

crossman

Senior Member
Location
Southeast Texas
Smart $ said:
Hmm... had an outside-the-box thought.

Is there any code which restricts running a solidly grounded circuit conductor from the primary system to X0 of the transformer?

If not, one could run such a conductor, and thus the xfmr would no longer be an SDS...???!!!

250.24(A)(5) prohibits a grounded conductor form being connected to ground or to the equipment ground on the load side of the service. Since X0 is typically required to have a SBJ to the EGC by 250.30(A)(1) and also typically must have bonding jumpers to the building steel and waterpipe as in 250.104, it seems that the primary side grounded conductor would be prohibited from being connected to X0.
 

crossman

Senior Member
Location
Southeast Texas
RB1 said:
I would also add that Don's proposal was spot on and should have been accepted.

And I agree also. The only concern is local ground faults to the building steel or to waterpipe, and that is taken care of by 250.104 in the parts concerning bonding of seperately derived systems to local building steel and waterpiping.

Example: Xfmr located on 20th floor should be bonded to building steel and metal waterpiping on the 20th floor if it is present.
 

Smart $

Esteemed Member
Location
Ohio
crossman said:
250.24(A)(5) prohibits a grounded conductor form being connected to ground or to the equipment ground on the load side of the service. Since X0 is typically required to have a SBJ to the EGC by 250.30(A)(1) and also typically must have bonding jumpers to the building steel and waterpipe as in 250.104, it seems that the primary side grounded conductor would be prohibited from being connected to X0.
...but those requirements, AFAICT, are for an SDS transformer. If a solidly grounded circuit conductor from the primary side is connected to X0, it is not an SDS. Therefore, no local electrodes required, no SBJ. Just an EGC which is not bonded to X0 (i.e. bonded only to xfmr non-ccc parts and continues on to disconnect, where it is not bonded to N terminal).
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I never really caught the fact that 250.30(A)(3) Ex 2 only applies when the transformer is an integral part of the service equipment, however that does not change my view that a correctly sized conductor run with the primary conductors to and through the switchgear to grounding electrode can be both the primary EGC and the secondary GEC. A tap from the conductor, within the switchgear, run to the equipment grounding terminal would be required and the rules in 250.64(C) and (E) would apply.
Don
 

ronaldrc

Senior Member
Location
Tennessee
Smart $ said:
Hmm... had an outside-the-box thought.

Is there any code which restricts running a solidly grounded circuit conductor from the primary system to X0 of the transformer?

If not, one could run such a conductor, and thus the xfmr would no longer be an SDS...???!!!

No as a matter of fact the NESC requires a jumper between your low voltage neutral that feeds your house and their high voltage primary neutral or grounded conductor. Same for commercial their same logic of fault clearing applies to residential and commercial.
 

crossman

Senior Member
Location
Southeast Texas
Smart $ said:
...but those requirements, AFAICT, are for an SDS transformer. If a solidly grounded circuit conductor from the primary side is connected to X0, it is not an SDS. Therefore, no local electrodes required, no SBJ. Just an EGC which is not bonded to X0 (i.e. bonded only to xfmr non-ccc parts and continues on to disconnect, where it is not bonded to N terminal).

Smart, you made me jump there. You may be on to something. If the solidly grounded circuit conductor of the primary is connected to X0 and feeds through to the secondary loads, essentially we have an autotransformer and it is not an SDS and X0 wouldn't need a SBJ or EGC or bonding to the steel or waterpipe.

Okay, I am gonna have to do some thinking on this one. Offhand, I can't think it would be proper, it just doesn't seem correct, ya know? But, I can't think of any Code sections which would prevent it, and I can't think of any theoretical reasons why it wouldn't work. Especially when we consider that a SDS xfmr X0 is actually bonded to the feeder grounded conductor through the SBJ and equipment grounds and MBJ at the service.

As I said, you may be on to something. Now, convincing the AHJ that the secondary is not an SDS may be another issue.

Anyway, good catch! Now let me think....
 
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TO SMART $,
Due to time constraints and what not, you guys are way ahead of me in your postings, and i am new to this forum and haven't figured out the cutting and pasting but, you asked if I had a particular installation question and the answer is no, other than referencing the original posting, which seemed to lead to SDS. I was wondering, if, in the example of a grounded B phase supply, whether or not the xfmr would still be considered a seperately derived system if any type of grounding conductor (connected to B phase) from the 480v supply was run to the xfmr and tied to the case w/ x0, hence a direct electrical connection between primary and secondary.
 

Smart $

Esteemed Member
Location
Ohio
ronaldrc said:
No as a matter of fact the NESC requires a jumper between your low voltage neutral that feeds your house and their high voltage primary neutral or grounded conductor. Same for commercial their same logic of fault clearing applies to residential and commercial.
We're not talking about a service transformer, aka primary transformer. We are discussing an on premises, consumer-owned and operated secondary transformer supplied by service power.
 

Smart $

Esteemed Member
Location
Ohio
automate0042 said:
TO SMART $,
Due to time constraints and what not, you guys are way ahead of me in your postings, and i am new to this forum and haven't figured out the cutting and pasting but, you asked if I had a particular installation question and the answer is no, other than referencing the original posting, which seemed to lead to SDS. I was wondering, if, in the example of a grounded B phase supply, whether or not the xfmr would still be considered a seperately derived system if any type of grounding conductor (connected to B phase) from the 480v supply was run to the xfmr and tied to the case w/ x0, hence a direct electrical connection between primary and secondary.
The problem is, whether it be that of the original posting or the case that you bring up, the NEC does not consider grounding conductors (as opposed to grounded conductors) as a direct electrical connection even though any one with minimal electrical knowledge knows this to be a universally false concept when the X0 terminal is bonded, as required, to the EGC of both primary and secondary systems, regardless of any other grounding or grounded conductor.

We are currently debating a loophole, so to speak, where the load side of secondary transfomer is not considered to be a separately derived system when X0 is intentionally connected to a supply side grounded [circuit] conductor.
 

quogueelectric

Senior Member
Location
new york
alternate theory

alternate theory

Use the pipe as the gec therefore and quantumly eliminating the choke effect that is in argumentum ad neauseum of the code change proposal.
 

Smart $

Esteemed Member
Location
Ohio
don_resqcapt19 said:
I never really caught the fact that 250.30(A)(3) Ex 2 only applies when the transformer is an integral part of the service equipment, however that does not change my view that a correctly sized conductor run with the primary conductors to and through the switchgear to grounding electrode can be both the primary EGC and the secondary GEC. A tap from the conductor, within the switchgear, run to the equipment grounding terminal would be required and the rules in 250.64(C) and (E) would apply.
Don
While I understand what you mean, I believe your proposal was rejected mostly because it was misleading... essentially the part where you wrote "...a grounding electrode shall not be required." You should have stated something to the effect of extending the primary GEC to the SDS system within the exception wording. Without that, the cmp probably looked at your proposal as not requiring any connection to grounding electrodes.

Another thing is that the combo GEC/EGC needs to be sized by GEC requirements.
 
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don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
quoqueelectric,
Use the pipe as the gec therefore and quantumly eliminating the choke effect that is in argumentum ad neauseum of the code change proposal.
What code section pemits you to use conduit as a GEC?
Don
 

ronaldrc

Senior Member
Location
Tennessee
I understood you where not talking about a utility transformer.

But the NEC treats any SDS the same way just because the transformer is in the building doesn't mean you don't have to hook it to the earth grounding electrode on that buildings electrical system.

And even if the primary and secondary grounded conductors are bonded as the NESC requires doesn't mean it is not a SDS.
 
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