Ground Rod Needed, Yes

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CCCI

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Orlando, Florida
I am a maintenance electrician and have been doing service and new constuction for over 20 years as an electrician. I just need some Back Up on a grounding problem. We have an electrical cotractor here because we have alot of electrical work right now.
The contractor put in a transformer/panel combo unit (15 KVA) and they did not put in a ground rod. I asked them about the ground rod and they said that it did not need one because the branch circuit had a ground and that bonded everything. I know that it needs a ground rod and would just like for someone to tell me that I am not stupid.
It needs a return path to its source and the source would be the new 15KVA transformer not the 150KVA over 1000' away.
Please tell me that I do not need to return my Master Electrician Card.
 
It is not a simple as that. I am not sure you do need a ground rod. I know that if you don?t install a ground rod, or otherwise connect the transformer secondary neutral point to some suitable grounding electrode, then you will not have a separately derived system. That will impact the manner in which equipment grounding conductors need to be connected. But I am not certain how to make that work properly. Someone else will have to address this part of your question.

I will say that a ground rod has nothing to do with a ?return path to its source.? That part you have wrong. The return path will be one of the other circuit wires (i.e., the grounded conductor for a single phase circuit, or another ungrounded conductor for a three phase circuit). You are right, however, in saying the source is the 15KVA transformer, not a component further upstream.

I will also say that the fact that a branch circuit (I presume this was referring to a load on the 15KVA transformer) has a ?ground? does not fulfill any requirements related to a ground rod. Your contractor is wrong about that.
 
The transformer needs to be grounded to the grounding electrode system of the building. A separate isolated ground rod would not be acceptable. Take a look at 250.30 for the grounding and bonding requirements for separately derived systems.

It needs a return path to its source and the source would be the new 15KVA transformer not the 150KVA over 1000' away.
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The grounding electrode system does not provide the low impedance fault current path back to the transformer. The system bonding jumper and the equipment grounding conductors form the effective ground fault current path.

Chris
 
Outside

Outside

The transformer is outside, about 2000' from any building. The branch circuit that I said had a grounding condutor in it is the feed for the transformer.
I see this as a SEPARATELY DERIVED SYSTEM and see it as needing a GROUNDING ELECTRODE SYSTEM. I have no building or metal to bond. The electrical contractor says that he is using the ground wire from the transformer feed to GROUND the transformer.
I believe that this is a SEPARATELY DERIVED SYSTEM and should have its own GROUNDING ELECTRODE SYSTEM and that a GROUND ROD would be the best way to provide the GROUNDING ELECTRODE SYSTEM. The GROUNDING conductor that the electrical contractor talked about is only a BONDING conductor. I believe that the GROUND ROD would help to stabilize the line-to-earth voltage during normal operation and is required by NEC 250.30 (a) (3) 2005.
Is this correct? I just wanted to make my first posting a little more clear.
Thank You
 
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CCCI said:
The transformer is outside, about 2000' from any building. The branch circuit that I said had a grounding condutor in it is the feed for the transformer.
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So just what is this transformer supplying?

At that distance and the size I am assuming it might be for some type of gate opener and or card reader.

If so then the pedestal that is installed would fit the description of a structure as outlined in Article 100 of the NEC.

Now Article 225 comes into play as the branch circuit or feeders are installed outside. This will require that a disconnect for the circuit supplying the primary of the transformer be installed at that structure and the disconnect be rated for service equipment. A grounding electrode system will be required to be installed at this structure as outlined in 250.32.
Should any type of conductor such as video or audio be mounted on the pedestal then an equipment grounding conductor will be required to be installed with the circuit supplying the transformer as outlined in 250.32(B).

The secondary of the transformer will be required to bond to this grounding electrode system as outlined in 250.30.
 
Gazebo

Gazebo

This transformer is going the power some receptacles and small lighting around a gazebo next to a small lake. It will also have some audio system on the post and time clocks for landscaping spriklers and the lights.
 
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CCCI: There are a variety of possible answers BUT to give you the best answer, which may or may not be the one you want to here, you really need to supply us with the COMPLETE details regarding the installation.
 
The primary on the transformer must have a EGC back to the source to clear a line to case fault.
The transformer, if seperatly derived must have a grounding electrode system per 250.30, and a system bonding jumper per 250.30(A)(1). The grounding electrode conductor terminates at the same point where the SBJ is installed 250.30(A)(3).
The grounding electrode system stablizes the secondary voltage on the transformer and protects against line surges/lightning.
Don't overthink this, but the primary EGC is bonded to the transformer case, the transformer case is bonded to the secondary EGC via the SBJ. But you still need a ground rod, a in a lighting strike the impedance of the primay EGC will be almost infinate.
 
CCCI said:
The transformer is outside, about 2000' from any building.
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CCCI said:
This transformer is going the power some receptacles and small lighting around a gazebo next to a small lake.
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See this post and replace the pedestal with gazebo.
This gazebo is a structure and will require a disconnect as outlined in 225.30 through 225.39 and a grounding electrode system as outlined in 250.32.

The secondary of the transformer will then bond to this electrode system as outlined in 250.30
 
jwelectric said:
This gazebo is a structure and will require a disconnect as outlined in 225.30 through 225.39 and a grounding electrode system as outlined in 250.32.

The secondary of the transformer will then bond to this electrode system as outlined in 250.30
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I agree with Mike entirly. :) :cool:
 
Gazebo - NO POWER

Gazebo - NO POWER

No power will be on the gazebo. The power and lights will be around the gazebo area and the transformer/panel combo unit will be on a post about 50' away from the gazebo.
 
CCCI said:
No power will be on the gazebo. The power and lights will be around the gazebo area and the transformer/panel combo unit will be on a post about 50' away from the gazebo.
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Unless that post grew there it is a structure and everything I have posted will apply.
 
CCCI said:
The transformer is outside, about 2000' from any building. The branch circuit that I said had a grounding condutor in it is the feed for the transformer.
I see this as a SEPARATELY DERIVED SYSTEM and see it as needing a GROUNDING ELECTRODE SYSTEM. I have no building or metal to bond. The electrical contractor says that he is using the ground wire from the transformer feed to GROUND the transformer.
I believe that this is a SEPARATELY DERIVED SYSTEM and should have its own GROUNDING ELECTRODE SYSTEM and that a GROUND ROD would be the best way to provide the GROUNDING ELECTRODE SYSTEM. The GROUNDING conductor that the electrical contractor talked about is only a BONDING conductor. I believe that the GROUND ROD would help to stabilize the line-to-earth voltage during normal operation and is required by NEC 250.30 (a) (3) 2005.
Is this correct? I just wanted to make my first posting a little more clear.
Thank You
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where does the code say an SDS has to have its own GES?
 
petersonra said:
where does the code say an SDS has to have its own GES?
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See 250.20(D) which will take you to 250.30.

Roger
 
roger said:
See 250.20(D) which will take you to 250.30.

Roger
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I see no where it actually says that. In fact what it does say is:

250.30A
7) Grounding Electrode. The grounding electrode shall be
as near as practicable to and preferably in the same area as the
grounding electrode conductor connection to the system. The
grounding electrode shall be the nearest one of the following:
(1) Metal water pipe grounding electrode as specified in
250.52(A)(1)
(2) Structural metal grounding electrode as specified in
250.52(A)(2)
Exception No. 1: Any of the other electrodes identified in
250.52(A) shall be used where the electrodes specified by
250.30(A)(7) are not available.
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That would imply pretty strongly to me that an existing GE is prefered, but that you can make one if you have to. Nothing that I see prohibits you from using an existing GE.
 
petersonra said:
I see no where it actually says that. In fact what it does say is:



That would imply pretty strongly to me that an existing GE is prefered, but that you can make one if you have to. Nothing that I see prohibits you from using an existing GE.
Click to expand...

I said that it is not close to any EXISTING GE. It is just a transformer on a post about 2000' from a building. A gazebo will be going about 50' from it and the gazebo will not have power on it.
 
No Existing Grounding Electrode

No Existing Grounding Electrode

raider1 said:
The transformer needs to be grounded to the grounding electrode system of the building. A separate isolated ground rod would not be acceptable. Take a look at 250.30 for the grounding and bonding requirements for separately derived systems.

Chris
Click to expand...

I'm not looking to add a GE, I do not have anything but a grounding conductor in the feed to the transformer itself.
It is a 480 volt single phase (two hots and a grounding conductor) to 240/120 volt single phase 15 KVA transformer/panel (a combo unit). The only grounds in the transformer is the grounding conductor from the feed to the transformer and the branch circuits that feed out of the panel to the lights and outlets.
 
CCCI,

I agree with you, the EGC run to the transformer is most likely not sized

large enough for the GES. The ground rod is the simplest method. All the EGC's and the GEC tie together anyway, don't

forget the SBJ.

edit: to add last comment.
 
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The simplest way to do this job is to use a Sq D Mini Power Zone, its a primary-transformer-secondary panel all in one.
Three wires on the primary, 2 ground rods and you are done.
 
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