GES for a transformer a long ways away

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Bjenks

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I need a little help on how electrical contractors handle the following:
A 480V 3 phase service is brought in to the middle of a field that has a service disconnect and a panel. A ground rod is driven and the panels neutral is bonded to the ground and then the rod for a separately derived system.

Now about 500 feet away a small motor control panel and convenience outlet is installed, however this motor controller requires 208/120 3 phase. The solution has been determined to install a transformer at the control panel that is over 2kVA to step the voltage down. This situation is set up only to ask a hypothetical question so the answer is not to do it differently.

My understanding of the code is that the neutral must be bonded to the ground that was fed from the service as the transformer is a separately derived source. Also a ground rod would be installed at the output of the transformer and bonded to derived neutral. Also the ground rod will need to be bonded to the services GEC 500 feet back.

1) Is this correct or is there an exception I missed on running the GEC all the way back?
2) Since the conduit coming from the service had 3 phases and a bonding conductor, do I also need to install a GEC too in the conduit or would it go outside the conduit?
3) Couldn't I just make the bonding conductor the same size as the GEC and only install one conductor?

I can't seem to find any code to explain this situation and haven't found anyone to answer it.
 
Bjenks said:
I need a little help on how electrical contractors handle the following:
A 480V 3 phase service is brought in to the middle of a field that has a service disconnect and a panel. A ground rod is driven and the panels neutral is bonded to the ground and then the rod for a separately derived system.

Now about 500 feet away a small motor control panel and convenience outlet is installed, however this motor controller requires 208/120 3 phase. The solution has been determined to install a transformer at the control panel that is over 2kVA to step the voltage down. This situation is set up only to ask a hypothetical question so the answer is not to do it differently.

My understanding of the code is that the neutral must be bonded to the ground that was fed from the service as the transformer is a separately derived source. Also a ground rod would be installed at the output of the transformer and bonded to derived neutral. Also the ground rod will need to be bonded to the services GEC 500 feet back.

1) Is this correct or is there an exception I missed on running the GEC all the way back?
2) Since the conduit coming from the service had 3 phases and a bonding conductor, do I also need to install a GEC too in the conduit or would it go outside the conduit?
3) Couldn't I just make the bonding conductor the same size as the GEC and only install one conductor?

I can't seem to find any code to explain this situation and haven't found anyone to answer it.
Click to expand...


Did you try reading 250.30(A)(3)Grounding Electrode Conductor, Single separately Derived Stystem?? Also, (A)(7)
 
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From the service to the SDS you only run an EGC, no GEC.

At the SDS another GES must be established a GEC run from that and tied into the EGC and XO of the SDS.
 
I think I must have made some assumptions and thus my misunderstanding. To confirm a new isolated GES is established at every separately derived source and they are not required to be connected except by equipment bonding?

My assumptions came because in a multi-story buildings with transformers we tie the GEC to building steel which is the same building steel as the service and thus they are all connected to the same GES. However, I now see that as a coincident as they are in the same building. I was thinking they were required to all be tied to the same GES and have the equipment bonding.

This make much more sense now, thanks for clarifying this for me.
 
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