EGC or EBJ?

[charlie b]

I had thought this was simple and basic. Then I was put into a position where I had to go back and read the book again. Imagine that, having to deal with Charlie's Rule!

Situation: At the secondary of a 480 ? 120/208V transformer, I run one wire from XO to a ground bar in the electrical room, and there is another wire going from there to (eventually) planet earth. Let?s ignore them.

From the secondary, I run 5 wires to an MCB panel in the same room, and the N-G bond takes place inside that panel. Four of the wires are Phases A, B, C, and the neutral. What is the 5th wire? Is it an Equipment Grounding Conductor, to be sized per 250.122? Or is it an Equipment Bonding Jumper, to be sized per 250.66?

I designed it as an EGC. The Inspector says it should have been sized as an EBJ.

 

[Jim Shorts]

250.30(A)(1) would not allow the neutral to ground connection in the panelboard if you pulled 5 wires on the secondary (parallel path). The system bonding jumper is installed in the transformer in the installation that you described and the 5th wire would be an equipment grounding conductor that must be sized per table 250.122

 

[hardworkingstiff]

I had thought this was simple and basic. Then I was put into a position where I had to go back and read the book again. Imagine that, having to deal with Charlie's Rule!

Situation: At the secondary of a 480 ? 120/208V transformer, I run one wire from XO to a ground bar in the electrical room, and there is another wire going from there to (eventually) planet earth. Let?s ignore them.

From the secondary, I run 5 wires to an MCB panel in the same room, and the N-G bond takes place inside that panel. Four of the wires are Phases A, B, C, and the neutral. What is the 5th wire? Is it an Equipment Grounding Conductor, to be sized per 250.122? Or is it an Equipment Bonding Jumper, to be sized per 250.66?

I designed it as an EGC. The Inspector says it should have been sized as an EBJ.

Sounds like parallel paths for neutral current?

Is the EGC/EBJ the only conductor going to ground from the panel or did you leave the panel neutral/ground connection and hit the building steel?

 

[infinity]

How would you size the 5th wire according to 250.122? Is there an OCPD in between the secondary and the MCB panel? Since the 5th wire is on the line side of the MCB I say you'll need to use 250.66 to size that wire based on the size of the secondary conductors.

 

[steve66]

My money is on a system bonding jumper and 250.66.

What line in table 250.122 would you use, since there isn't any overcurrent protection between the transformer and the panel?

I don't think the location of the N-G bond makes any difference.

Steve

 

[Smart $]

...I run one wire from XO to a ground bar in the electrical room, and there is another wire going from there to (eventually) planet earth. Let’s ignore them.

We can't for the question asked.

Could you please elaborate as to the purpose of this ground bar (bus?) in the electrical room. Is it the ground bus for the service equipment? Is the service GES connected to this bus, directly or indirectly, and if indirectly, what size and type conductor makes the indirect connection?

 

[Smart $]

Ignore my last post, if you must...

What is the 5th wire? Is it an Equipment Grounding Conductor, to be sized per 250.122? Or is it an Equipment Bonding Jumper, to be sized per 250.66?

I designed it as an EGC. The Inspector says it should have been sized as an EBJ.

Inspector is correct... start at 250.30(A)(2), which takes you to 250.102(C), taking you to Table 250.66.

 

[barclayd]

Ignore my last post, if you must...


Inspector is correct... start at 250.30(A)(2), which takes you to 250.102(C), taking you to Table 250.66.

I agree - if that 'ground bar' is part of the 'Common Grounding Electrode Conductor' for the separately derived system.
The tap would be sized per 250.66.

db

 

[ibew441dc]

Read Charlies Rules Again.....

Read Charlies Rules Again.....

Is it an Equipment Grounding Conductor, to be sized per 250.122?

No.

Or is it an Equipment Bonding Jumper, to be sized per 250.66?

Yes

I designed it as an EGC. The Inspector says it should have been sized as an EBJ.

The inspector is correct based upon...

250.30(A)(2) Equipment Bonding Jumper Size. Where an equipment bonding jumper of the wire type is run with the derived phase conductors from the source of a separately derived system to the first disconnecting means, it shall be sized in accordance with 250.102(C), based on the size of the derived phase conductors.

It has been my experience that many will find this code section, rush to 250.102, forget about the (C) and go straight to (D)....

250.102(C) Size ? Equipment Bonding Jumper on Supply Side of Service.
250.102(D) Size ? Equipment Bonding Jumper on Load Side of Service.

Easy mistake to make if we are not thorough.

 

[charlie b]

I was out of the office yesterday afternoon, so I am just now getting back to this. Many thanks for the information. Here are a few answers to your questions, and a few questions of my own.

This is a remote electric room, not the main. The transformer establishes a new SDS. The ground bar in the room (a copper bar bolted to the wall) is there as a common bonding point, and the means of getting the transformer’s XO point to planet Earth. From that bar, conductors run to every other such bar in all the other remote electric rooms, and to local building steel if available, and to the similar bar in the main electric room. The GEC runs from the bar in the main electric room to one or more grounding electrodes.

Our design drawings and specifications did not explicitly direct the installer whether to place the N-G bond at the transformer, and therefore to separate N and G bars within the MCB panel, or whether to place that bond at the panel, and to separate N and G within the transformer. It is not common for an engineering design to include that level of detail. But am I not right in saying that either installation is acceptable? Am I not right in saying that in either case, the “ground wire thingy” is serving as an EGC? That is, if the N-G bond is at the transformer, then the 5th wire serves as the EGC for the panel’s enclosure (and its ground bus), and if the N-G bond is at the panel, then the 5th wire serves as the EGC for the transformer’s enclosure.

How would you size the 5th wire according to 250.122? Is there an OCPD in between the secondary and the MCB panel? Since the 5th wire is on the line side of the MCB I say you'll need to use 250.66 to size that wire based on the size of the secondary conductors.

This is a new consideration for me. I had not noticed before that the words “ahead of” appear in the top of the left-hand column of Table 250.122. Back to Charlie’s Rule again, I suppose. But I am allowed to protect the transformer secondary conductors using a breaker at their load side, if I follow the transformer tap rule requirements. Does that not carry with it the right to use the downstream breaker rating as the basis for sizing the 5th wire (given that I am not yet convinced it is not an EGC)?

 

[charlie b]

Let me address one more point made by Daniel. I will quote your quote of 250.30(A)(2), but put the emphasis on a different word:

Where an equipment bonding jumper of the wire type is run with the derived phase conductors from the source of a separately derived system to the first disconnecting means, it shall be sized in accordance with 250.102(C), based on the size of the derived phase conductors.

That word “where” tells me that (1) I don’t have to run an equipment bonding jumper with the derived phase conductors, and (2) If I choose to, then I must follow the rule it gives me. So if I run an EGC as I ask about above, and if I therefore do not run an EBJ, then can I say that this article does not apply to my installation?

 

[augie47]

The drawing may help.
All Bonding should be at one location. The transformer or the panel.
If you run the 5th conductor it should be sized be 250.66 as others have pointed out.
N-G Bond at the panel should only take place where all bonding including the electrode is done at the panel.

 

[charlie b]

The drawing may help.

Thanks, but it doesn't quite address my question. This drawing shows a single phase system, so we would be talking about the 4th wire here. But this drawing does not show the ground bus within the panel. If it had, I suppose there would have been a wire between that bus and the panel enclosure. But my question is about the wire between the ground bus in the panel and the transformer.

If in the upper of the two drawings (System Bonding Jumper is located at the transformer) there were a ground bar in the panel, and if the panel’s N and G bars were separated, and if the green wire shown between panel enclosure and transformer enclosure were instead shown as going between the panel’s ground bar and the transformer enclosure, would that wire not be an EGC? If not, why not?

 

[iwire]

That word ?where? tells me that (1) I don?t have to run an equipment bonding jumper with the derived phase conductors,

I am sure there are times you would not have to, in your case (480 ? 120/208V transformer) you must. :smile:

There is no way to use 250.122 without an OCPD ahead of it and I think it is safe to assume they mean ahead of it on the same source, not the primary side of a transformer.

 

[Twoskinsoneman]

Thanks, but it doesn't quite address my question. This drawing shows a single phase system, so we would be talking about the 4th wire here. But this drawing does not show the ground bus within the panel. If it had, I suppose there would have been a wire between that bus and the panel enclosure. But my question is about the wire between the ground bus in the panel and the transformer.

If in the upper of the two drawings (System Bonding Jumper is located at the transformer) there were a ground bar in the panel, and if the panel?s N and G bars were separated, and if the green wire shown between panel enclosure and transformer enclosure were instead shown as going between the panel?s ground bar and the transformer enclosure, would that wire not be an EGC? If not, why not?

I think I agree with charlie. If I understand correctly your situation more resembles the bottom picture right? You SBJ is in the disconnect right? the 5th wire seems to be an EGC run from the ground bus in the disconnect to connect the trans case right?

 

[charlie b]

If I understand correctly your situation more resembles the bottom picture right? You SBJ is in the disconnect right? the 5th wire seems to be an EGC run from the ground bus in the disconnect to connect the trans case right?

As I mentioned earlier, the engineering design package does not tell the installer whether to use the top picture or the bottom picture.

For the sake of discussion, let us say it is the bottom picture. That puts the MCB panel's main breaker ahead of the wire (EGC) going out to the transformer's enclosure, does it not?

 

[charlie b]

I am sure there are times you would not have to, in your case (480 ? 120/208V transformer) you must. :smile:

I am not saying I disagree with you Bob (although I have done that from time to time :smile. I just don't understand the nature of an EBJ. The Article 100 definition of that term talks about connecting two or more portions (plural) of the EGC (singular). I just can't make any sense out of that. In particular, I can't see how the 5th wire serves to connect two or more portions of an EGC.

 

[augie47]

any short ahead of your OCP device (at the transformer can, in the supply to the OCP, etc) would require bonding to be sized per 250.66. Any falult ahead of the secondary has no OCP to trip so you would treat it just as you do a service.

In this situation, since you already have a ground bar connected to XO for your grounding electrode connection, IMHO, you need a 5th wire to the panel which would serve as the ahead of OCP bond for the panel, and the path for the EGC to return power to the source.

 

[Honyock]

City of Irvine, CA-Electrical Inspector

City of Irvine, CA-Electrical Inspector

Go with the Inspector_250.30(A)(2)_250.102(C)_Table 250.66.

 

[al hildenbrand]

Any short ahead of your OCP device (at the transformer can, in the supply to the OCP, etc) would require bonding to be sized per 250.66. Any falult ahead of the secondary has no OCP to trip so you would treat it just as you do a service.

I think that's the heart of the matter, Charlie. A fault of an ungrounded conductor, at the transformer, to the transformer can, goes to the MBJ, which, in your case in the OP, is at the MCB Panel, before getting into the neutral and then returning to the secondary windings. The “ground wire thingy” has to be strong enough for the transformer primary protection to clear before the “ground wire thingy” sustains damage.