SDS bonding question

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derek22r

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I have recently started working at a new plant and have an issue with the way transformers are being grounded/bonded, but cannot find anything in the NEC stating it is wrong.

Basically for all transformers, the grounding electrode conductor connection is made at the transformer. Therefore the system bonding jumper is also installed at the transformer and routed with the phase conductors to the first disconnecting means. However once at the first disconnecting means, the system bonding jumper is terminated to the disconnect enclosure, and the ground bus is bonded to the enclosure.

I know (I think) that the system bonding jumper should terminate to the ground bus, but cannot find where this is stated in the NEC. Am I right, or is it OK to bond the system through the enclosure.
 

Smart $

Esteemed Member
Location
Ohio
You are mixing terms.

A system bonding jumper (SBJ) never leaves the equipment in which it is located. One end is connected to the grounded conductor( or its terminal) while the other end is connected to the grounding bar/bus/terminal. The GEC can be connected at either end of the SBJ. This is the only location where grounded and grounding conductors are connected together intentionally per each isolated-power system.

If this location is at the transformer, and if a grounding conductor (called an Equipment Bonding Jumper, or EBJ for short) is run to the disconnect, yes it has to be terminated to the grounding bar/bus/terminal. Connecting to the enclosure is fine if that is the grounding terminal. Yet as you suspect, it is likely not if the enclosure contains a grounding bar or bus. I'm not certain of the article number right now, or if there even is one that explicitly states this. It may fall back on the listing and manufacturers instructions. If I get a chance I'll try to find a directly applicable code...
 

Smart $

Esteemed Member
Location
Ohio
The sections which seem to directly apply are 250.102(B) which takes you to 250.8... yet there is no explicit requirement there.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Take a look at 250.30 for the grounding requirements of separately derived alternating current system. Specifically 250.30(A)(1) for the system bonding jumper, also look at the last sentence of 250.30(A)(3) for the grounding electrode conductor for a single separately derived system.

Chris
 

raider1

Senior Member
Staff member
Location
Logan, Utah
The sections which seem to directly apply are 250.102(B) which takes you to 250.8... yet there is no explicit requirement there.

If you are talking about the equipment bonding jumper start with 250.30(A)(2) which will direct you to 250.102(C) for sizing the equipment bonding jumper.

Chris
 

derek22r

Member
A system bonding jumper (SBJ) never leaves the equipment in which it is located. ...

I believe Exhibit 250.13 in the 2005 NEC shows the SBJ being routed from the Transformer to the disconnect. Am I interpreting this illustration wrong.
 

Smart $

Esteemed Member
Location
Ohio
I believe Exhibit 250.13 in the 2005 NEC shows the SBJ being routed from the Transformer to the disconnect. Am I interpreting this illustration wrong.
Since you say "Exhibit", I'm assuming that is from the NEC Handbook, which I do not have...
 

raider1

Senior Member
Staff member
Location
Logan, Utah
I believe Exhibit 250.13 in the 2005 NEC shows the SBJ being routed from the Transformer to the disconnect. Am I interpreting this illustration wrong.

Exhibits in the NEC handbook are not part of the code but just the opinion of the author of the book.

Chris
 

jcole

Senior Member
I believe Exhibit 250.13 in the 2005 NEC shows the SBJ being routed from the Transformer to the disconnect. Am I interpreting this illustration wrong.

Yes you are correct. But the code also allows the connection to be made at the first disconnecting means. Which would prevent you from having to run the sbj from the transformer to first disconnecting means. Therefore, not having to run 5 conductors. Per 250.30A(1).

Just think about what the sbj does. Connects the grounded conductor to equipment grounding conductors. According to code above, this can be done anywhere from source to first disconnecting means. So why would you run a fifth conductor instead of using a screw,strap,bar,etc. that comes with the panel?

Just remember the stuff in blue and exhibits are authors opinion of code like raider1 said. But IMO they are very useful.
 

derek22r

Member
This is the book I have always used (I'm very young). I'm getting the impression that you don't agree with some of it's writings.

I always thought that this book was put out by the NEC. Surely it would have to be approved by the NEC, right?

Do you agree with this statement "The location of the grounding electrode conductor connection to the grounded conductor must be at the same point as where the bonding jumper is connected to the grounded conductor". This is one of the comments from this book that it sounds like you don't agree with.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
I always thought that this book was put out by the NEC. Surely it would have to be approved by the NEC, right?

The NEC handbook is published by the NFPA, the same people who publish the NEC. The problem is that States adopt the NEC not the NEC handbook as code. The commentary is useful to help understand the intent and purpose of the code sections, but the commentary can't be cited as a legally binding requirement.

Do you agree with this statement "The location of the grounding electrode conductor connection to the grounded conductor must be at the same point as where the bonding jumper is connected to the grounded conductor". This is one of the comments from this book that it sounds like you don't agree with.

One of the problems with this statement is the term "bonding jumper". There are 2 distinct types of bonding jumpers in regards to a transformer secondary, a "System bonding jumper" and an "Equipment bonding jumper". Using the term "bonding jumper" in this instance is vague

Chris
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Yes you are correct. But the code also allows the connection to be made at the first disconnecting means. Which would prevent you from having to run the sbj from the transformer to first disconnecting means. Therefore, not having to run 5 conductors. Per 250.30A(1).
...
The number of conductors required by the code between the transformer and the first disconnect does not change based on where the bonding connection is made. The same number of conductors are required in either case.
 

Smart $

Esteemed Member
Location
Ohio
If you are talking about the equipment bonding jumper start with 250.30(A)(2) which will direct you to 250.102(C) for sizing the equipment bonding jumper.

Chris
Yes I was referring to the EBJ... but my reply was regarding my first post to the thread and the EBJ's termination to the enclosure itself rather than the grounding bus located within same enclosure. I could find no code section which explicitly says it has to be terminated to the ground bus. However, I believe this comes back to installing per manufacturers instructions and the ground bus being the specified grounding terminal for the enclosure.
 

derek22r

Member
Now I'm second guessing everything I thought I new. The attachment shows the exact configuration I have been trying to describe.

So you see any issues with it? What would you call the conductor (if anything) between the neutral and the transformer enclosure?
 

jcole

Senior Member
The number of conductors required by the code between the transformer and the first disconnect does not change based on where the bonding connection is made. The same number of conductors are required in either case.

Sorry I didnt know a conductor had to be used. I always used metal conduit as the bonding between the transformer and first disconnecting means enclosure. Never failed inspection on the few jobs I did this way. But that doesnt mean anything around here.

Could you give me the code that says a conductor had to be used?

Sorry for the bad info dereck22r.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Now I'm second guessing everything I thought I new. The attachment shows the exact configuration I have been trying to describe.

So you see any issues with it? What would you call the conductor (if anything) between the neutral and the transformer enclosure?

IMHO in the drawing that you provided the wire from the neutral bar in the transformer to the transformer enclosure would be the system bonding jumper, and the wire from the transformer enclosure to the first disconnecting means enclosure would be an equipment bonding jumper.

Chris
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Sorry I didnt know a conductor had to be used. I always used metal conduit as the bonding between the transformer and first disconnecting means enclosure. Never failed inspection on the few jobs I did this way. But that doesnt mean anything around here.

Could you give me the code that says a conductor had to be used?

Sorry for the bad info dereck22r.
Per 250.118 the conduit is an EGC.
 

jcole

Senior Member
Per 250.118 the conduit is an EGC.

Ok. I think I understand what your saying. Metal conduit can only be used as an egc not an ebj.

I also understand that egc's only exist after the sbj.

So what I am understanding is that the only difference between a egc and ebj is one is on the load side of sbj and the other on the line side. But they do the exact same thing: Form an effective ground fault current path. So I wonder why the rules are different for one and the other?

Thanks for clearing this up for me.
 

Smart $

Esteemed Member
Location
Ohio
So you see any issues with it?
Yeah... it's a piss poor example, even though it is to code. It doesn't even depict an SBJ because it uses one bus for all connections, and the depicted EBJ is actually only an EGC.

The following image is how the code actually dubs the jumpers and connections. Take note that I flopped the grounding block and the neutral block in the disconnecting means so as not to cross wires. As depicted, this is not the only code compliant way to make the connections. The GEC is permitted to be landed on the other end of the SBJ.

SDSBonding.gif
 
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