Bonding junction

[Dbronx]

I want to bond a branch circuit junction box that is shared by two 225 amp sub panels fed from a 800 amp MDP, tied to 2 ground rods. The MDP it 5 wire from Transformer, are sub panels are a 5 wire from MDP, the sub panels are tied to a common ground electrode and 2 ground rods. I want to bond the ground bars from sub panels to junction box with #4 wire.

Question 1 Is it code to bond both sub panels to 1 junction?

Question 2 will I create a ground loop.

 

[Dbronx]

This is a drawing of system

View attachment gorond rods.pdf

 

[Dennis Alwon]

What is the box at the top of the drawing? Meter? Also the grounding electrode conductor seem to be spliced- are they irreversible. Why not just go directly to the rods?

Edit
Now I see that these are sub panels- they don't get connected to the grounding electrode.

 

[petersonra]

I am not entirely sure based on the information you have presented but I think that the GEC should go back to the xfmr and not the subpanels or MDP.

I am not sure what you mean by 5 wire. 3 hots, N, and G?

 

[Dbronx]

What is the box at the top of the drawing? Meter? Also the grounding electrode conductor seem to be spliced- are they irreversible. Why not just go directly to the rods?

The junction box is for the branch circuits of the two sub panels

The ground electrodes from the sub panels is a #6 are connected at a ground bar, from the ground bar is a 1/0 size common ground electrode art 250.58

Edit
Now I see that these are sub panels- they don't get connected to the grounding electrode.

The MDP is outside and sub panels are in building

 

[Dbronx]

I am not entirely sure based on the information you have presented but I think that the GEC should go back to the xfmr and not the subpanels or MDP.

I am not sure what you mean by 5 wire. 3 hots, N, and G?

5 wire is three phase conductors, neutral and EGC

 

[Dennis Alwon]

Yiou need the grounding electrode conductor at the mdp not the sub panels. I am assuming the mdp is attached to the building

 

[david]

I am not entirely sure based on the information you have presented but I think that the GEC should go back to the xfmr and not the subpanels or MDP.

I am not sure what you mean by 5 wire. 3 hots, N, and G?

250.24(2)
Bob I do not see a problem grounding at the transformer and also at the MDP (service). I would ask why the 5th wire from the transformer to the MDP and what is it connected to at both places. I would be concerned that, what was intended to be an equipment ground, is actually a parallel neutral from the transformer to the MDP

 

[david]

Yiou need the grounding electrode conductor at the mdp not the sub panels. I am assuming the mdp is attached to the building

From the OP 5 wires from the MDP to the sub panels. If that was run correctly then the Neutral buses are isolated from the equipment grounds. Assuming that is correct, then we have some unnecessary re-earthling but no violation. If the ?sub-panels? are correct even if the equipment grounds are re-earthed then bonding the ground rods to the junction enclosure will not create a violation.

I agree with Dennis in trying to explaining how this should have looked.

 

[petersonra]

Yiou need the grounding electrode conductor at the mdp not the sub panels. I am assuming the mdp is attached to the building

The OP says 5 wire from xfmr to MDP.

 

[david]

I want to bond the ground bars from sub panels to junction box with #4 wire.

Question 1 Is it code to bond both sub panels to 1 junction?

Question 2 will I create a ground loop.

Why not just bond the equipment grounds in the Jbox to the enclosure you are trying to ground

 

[Smart $]

The OP says 5 wire from xfmr to MDP.

Need clarification whether transformer is service or separately derived system (SDS). 5-wire would be required if SDS.

 

[david]

Need clarification whether transformer is service or separately derived system (SDS). 5-wire would be required if SDS.

Assuming that the neutral at the MDP (building) is bonded to a grounding electrode system (i.e. ground rods, building steel, footer) and the SDS is outside 250.24(2) because it is not a transformer supplying a service then the neutral is no longer required to be earthed at the transformer. Is a system bonding jumper still required to be run from the SDS to the MDP at the building?

 

[Smart $]

Assuming that the neutral at the MDP (building) is bonded to a grounding electrode system (i.e. ground rods, building steel, footer) and the SDS is outside 250.24(2) because it is not a transformer supplying a service then the neutral is no longer required to be earthed at the transformer. Is a system bonding jumper still required to be run from the SDS to the MDP at the building?

For an SDS, it does not matter where it is located, a Supply-Side Bonding Jumper (SSBJ) is required [250.30(A)(2)]

 

[david]

Need clarification whether transformer is service or separately derived system (SDS). 5-wire would be required if SDS.

Sorry I should have been more clear with the question. I agree that a equipment bonding jumper is required to bond the system neutral to the equipment grounds. My question is if that eguipment bonding jumper is a the point of the first disconnect (MDP)at the building is the 5th wire still required to be run from the SDS when it is outside to the MDP at he building. 250.30 says where an equipment bonding jumper not that it shall be run. Is the 5th wire required when the SDS is outside?

 

[Smart $]

Sorry I should have been more clear with the question. I agree that a equipment bonding jumper is required to bond the system neutral to the equipment grounds. My question is if that eguipment bonding jumper is a the point of the first disconnect (MDP)at the building is the 5th wire still required to be run from the SDS when it is outside to the MDP at he building. 250.30 says where an equipment bonding jumper not that it shall be run. Is the 5th wire required when the SDS is outside?

I answered your question in Post #15. It doesn't matter where the System Bonding Jumper (SBJ) is located, a Supply-Side Bonding Jumper (SSBJ) is always required for an SDS. It is essentially an "equipment grounding conductor" (EGC)... it is called an SSBJ because EGC's only exist on the load side of a system disconnecting means (and use different sizing rules).

 

[david]

I answered your question in Post #15. It doesn't matter where the System Bonding Jumper (SBJ) is located, a Supply-Side Bonding Jumper (SSBJ) is always required for an SDS. It is essentially an "equipment grounding conductor" (EGC)... it is called an SSBJ because EGC's only exist on the load side of a system disconnecting means (and use different sizing rules).

sorry it is my understanding that the 5th wire is not required from the transformer (SDS) to the MDP

It was my understanding that when you have an SDS outside you could still earth the neutral at the outside SDS similar to how 250.24 (2) would require a service transformers neutral to be earthed at the transformer.
You could then size the neutral 250.30(8)

you could if you wanted earthed the neutral at both the SDS and the MDP (building main disconnect) use 250.30 (1) exception no. 2;.

You would not need an equipment bonding jumper in accordance with 250.30 (2) since you where bonding the neutral (250.30(8) neutral / equipment bonding jumper )again at the MDP using a System Bonding Jumper250.30(1) at the MDP

 

[Smart $]

sorry it is my understanding that the 5th wire is not required from the transformer (SDS) to the MDP

It was my understanding that when you have an SDS outside you could still earth the neutral at the outside SDS similar to how 250.24 (2) would require a service transformers neutral to be earthed at the transformer.
You could then size the neutral 250.30(8)

you could if you wanted earthed the neutral at both the SDS and the MDP (building main disconnect) use 250.30 (1) exception no. 2;.

You would not need an equipment bonding jumper in accordance with 250.30 (2) since you where bonding the neutral (250.30(8) neutral / equipment bonding jumper )again at the MDP using a System Bonding Jumper250.30(1) at the MDP

No disrespect intended, but your prior understanding was incorrect.

FWIW, 250.30(C) was added to the 2011 NEC requiring a grounding electrode connection for outdoor sources. It seems to be interpretted in two different ways: 1) a grounding electrode must be installed at the outdoor SDS and connection made thereto, or 2) a grounding electrode conductor must be run in addition to the derived conductors and the SSBJ. I disagree with the latter interpretation, but for those that do, a sixth wire would be required.

 

[david]

No disrespect intended,

As you have eluted to we have not adopted the 2011 NEC still on 2008.

I may be to simplistic in my thinking and I have learned to give your experience and knowledge of the code a second or third look. I don?t take for granted what you say when you express your thoughts.

I would have thought after looking at 250.30 (A)(2) Supply-Side Bonding Jumper and 250.30(A)(3)Grounded Conductor would be coupled together in that 250.30(A)(2) would apply when no Grounded conductor is present, and 250.30(A) (3) would apply when a grounded conductor is present on SDS systems. Especially when you consider that the outside transformer must now be earthed and you must comply with 250.30(1) exception NO. 2 eliminating parallel paths for neutral current.

It seems to me the purpose for requiring the Supply side bonding jumper was in establishing a fault clearing path back to the source. The supply side bonding jumper would take away any guess work as to the fault clearing path for a system that is 480V verses a system that is 480/277V.
The fault clearing path between the 480V. system really couldn?t be called a neutral and calling it a grounded conductor was confusing. Calling it a supply side bonding jumper seems to take away the confusion that a path must be established back to the source.

Looking at 250.4(3) Bonding of electrical Equipment and 250.6 Objectionable Current.
Why would two parallel paths be required back to a SDS source in a case when the source is outside and required to be earthed and bonded to the transformers enclosure?

 

[Smart $]

... 250.6 Objectionable Current.
Why would two parallel paths be required back to a SDS source in a case when the source is outside and required to be earthed and bonded to the transformers enclosure?

Per 250.6, you wouldn't have, or would eliminate a parallel path with regard to any grounded conductor. If the SBJ is at the source, then you wouldn't have a second at the disconnect, and vice versa. In other words, you'd keep grounded and grounding conductors isolated at all but the location of the SBJ. As for the redundancy compared to a service transformer, I can only surmise the CMP has there own idea on what grounding is necessary.