service bonding

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paul renshaw

paul renshaw

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Cordova, Maryland
We have a facility nearing completion wired by an outside contractor that we are doing some inspections on. There is a 25kv loop that feeds a xfmr at each bldg, that is 480/277wye secondary. There is a ground rod system for each building that is bonded to the XO of the xfmr. There are five wires run from the service panel to the xfmr, with the neutral and ground split at the service panel. Normally you bond the N/G at the service. In this case, would the 25kv originating switchgear from the utility be considered the service and the lines into the building considered feeders? Should there be another seperate GEC run to the panel, or since the one coming to the panel is connected to the GEC in the xfmr, would it be redundant. The GEC from the ground rods runs straight to the xfmr and terminates in the same place as the Neutral and Grounding conductor that runs to the panel in the building. Also, the secondary that comes into the building panel is unfused, and where they enter into a trough, branch circuit wires join them in the same raceway, I know that is a violation if these are considered service conductors, but are they considered service conductors? Sorry so long, just wanted to get info correct.
 
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The xfmrs and 25kv feeders are owned by the facility, and installed by the GC on the job. The grounding situation seems the same, but the ownership is different. They pick up the 25kv from the poco and go to a seperate xfmr at each of the five buildings.
 
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Oh! I re-read your post.:roll:

That is somewhat out of the scope of my knowledge. Industrial is a whole different animal, maybe some of the other guys could help?
 
Paul,
I don't think any of the conductors are service conductors. It appears that they are all after the service point and would all be feeders. If the transformer is remote from the buildings served, then I think that 250.32 will require a grounding electrode connection at the building to the EGC from the transformer. Other wires are permitted to be in the same raceway or wireway as the feeder conductors. Don't forget that 225.32 requires that the feeder have its disconnect "nearest the point of entrance" of the feeder conductors to the building. This is also the where the feeder OCPD must be installed, assuming that there is not one at the secondary of the transformer, per 240.21(C)(5).
Don
 
The xfmr sits right outside of the building, and the EGC from the xfmr to the building is connected to the GEC, that goes to the rods. The GEC for the building system, that goes to the rods, physically runs from the rods direct to the xfmr, and is tied to XO, neutral wire to building, and EGC to building. The rods are located outside of the building between the building and the outdoor xfmr. Running another wire would have to go from the equipment ground bus in the panel, to the xfmr, of which there is already one in place(EGC). Also, there are some step down xfmrs in the service room, what do they use for their connection to the grounding electrode? Do they need to run out to GEC in the outside xfmr?
 
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250.32(B)1 states "An equipment grounding conductor as described in 250.118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). In this case it is connected to the grounding electrode conductor in the xfmr. Will that satisfy it or does it also need to go directly to the rods, which would be very difficult to do. I also noticed a 2 1/2 inch copper water line comes into the building and does not have a conductor run to it. Could they install one and meet the requirement? That would take it to a grounding electrode and comply with 250.50, which in my opinion it does not now by excluding the water pipe.
 
Paul,
In my opinion you have to run a GEC to the building disconnet. The water pipe would have to be used as one of the building grounding electrode and would have to have supplemental electrode(s) per 250.53(D)(2).
Don
 
So if they tie into the water line, and connect it to the bldg disc. means, they should be okay? That will tie the water pipe, footer ground, and rods all together. I found out today that a 4/0 cu runs between the rods, taps to the footer, and goes into the xfmr. They did leave out the water pipe though.
 
I have set many 15 KV transformers here in Central Fla and pulled the secondaries to the buildings MDP No grounds are pulled in these conduits only a neutral and 3 phase conductors. XO in the Utility Transformer is tied to the ground ring installed inside the throat of the transformer pad. The seondary neutral is bonded to the ground in the MDP as required.
 
Sam.
XO in the Utility Transformer is tied to the ground ring installed inside the throat of the transformer pad. The seondary neutral is bonded to the ground in the MDP as required.
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The key here is that you have an utility company transformer and in the case of this thread, we have a customer owned transformer, and while they are electrically identical, the code rules are not the same. However, in both cases a grounding electrode connection is required at the building. The only real difference is that in the case of the customer owned (SDS) transformer, you can't always bond the grounded conductor at both the building disconnect and the transformer.
Don
 
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Paul,
So if they tie into the water line, and connect it to the bldg disc. means, they should be okay? That will tie the water pipe, footer ground, and rods all together. I found out today that a 4/0 cu runs between the rods, taps to the footer, and goes into the xfmr.
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As long as you do not make a grounded to grounding bond at the building disconnect, you will be in compliance with the code. The fact that the rebar is used for the transformer grounding electrode triggers an installation per 250.32(B)(1).
Don
 
Sam,

The difference here is that the conductors you reference are considered service conductors, whereas these are considered feeders because of the location of the service point. The service point is the switch that picks up the 25kv from the poco, thus the lines to the buildings and xfmrs are defined as feeders.
 
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