Bonding ground to Neutral

K

Kershawrobotics

Member
Location
League City, Tx
Occupation
Master Electrician
The drawing below covers a ground to neutral bonding application. The question is "Can/should the earth ground be connected to the breaker panel neutral bar? What NEC code section has the answer?"

https://drive.google.com/file/d/1K8IxzwcTbN3NBCgziyqvUiI-HLlSK2i6/view?usp=sharing

If the drawing cannot be accessed, I will try to explain the issue. Grid power (480VAC 3Φ) feeds a UPS, then UPS power feeds a 480VAC 1Φ to 240/120VAC 1Φ transformer. The earth ground wire is connected to the center tapped neutral at the transformer. The transformer feeds a 240/120VAC 1Φ breaker panel. Breakers (120VAC 1Φ) feed 20A receptacles that power a crane control system. Earth ground is connected to the neutral bus bar inside the breaker panel. There is no ground rod at the transformer. Earth ground originates at the grid power connection.
 
Not sure what you mean by "earth ground originates at the power grid connections".

The secondary of the transformer requires a connection to a grounding electrode system using a grounding electrode conductor.

If this connection was made at the transformer, you cannot not bond the neutral again at the panel.
 
Earth ground starts at a grounding ring system at the building electrical distribution room, which is 100 feet from the 240/120VAC transformer. Everything, including the crane is inside the same building.

Referencing my statement: "There is no ground rod at the transformer." Your comment means a ground rod must be located at the transformer?
NEC code section?
 
To "Don_resqcapt19": Your answer means the ground wire cannot be connected to the neutral bar in the breaker panel. Which is what I suspected.
To "jim dungar": Thanks for clarification on grounding electrode. Everything is bonded to ground at multiple points including building frame.

I need to research applicable NEC articles for ammunition to discuss the issue with the electrical engineers. Any help is appreciated.
 
Were confused by the term earth ground. Isn't it just a grounding electrode? Your drawing might be helpful but it cannot be viewed without a sign in.
 
I think the op is saying the drawing is showing the neutral/ground bond is at the panel, not the transformer, though common practice is at the transformer, it can be in either place.
 
Background: I have a master electrician license but I have not worked in construction for 40 years. I work at a government site where electrical engineers design complex systems, yet they are not NEC experts. It falls to me to solve code issues on projects I install.

Problem: The panel/neutral grounding issue is similar to a subpanel installation, if this was fed straight from a utility source. My confusion is how to categorize the panel when it is derived from a transformer through a UPS. The concern is ensuring electrical safety in the event of a short to ground. The 120VAC receptacles are fed from AFCI/GFCI breakers. I think the breaker panel neutral bar is isolated from the breaker box.
 
Kershawrobotics said:
Earth ground starts at a grounding ring system at the building electrical distribution room, which is 100 feet from the 240/120VAC transformer. Everything, including the crane is inside the same building.

Referencing my statement: "There is no ground rod at the transformer." Your comment means a ground rod must be located at the transformer?
NEC code section?
Click to expand...
The rules are found in 250.30 that has references to other rules.
Not that the grounding electrode has to be at the transformer, but the grounded conductor must be connected to a grounding electrode via a grounding electrode conductor.
 
To "jim dungar": That was my confusion. Subpanel versus separately derived system. Thank you, now I know where to search.
To "Don_resqcapt19": Thank you for the code section.
To "Little Bill": No, it is not a dwelling. This is not about meeting code requirements. We will have people suspended from an artificial gravity crane, in suits that could accidently become energized, so human safety is paramount.
 
Kershawrobotics said:
To "Little Bill": No, it is not a dwelling. This is not about meeting code requirements. We will have people suspended from an artificial gravity crane, in suits that could accidently become energized, so human safety is paramount.
Click to expand...
AFCI is not really about protecting people, it's more about protecting hidden wiring whereas GFCI is about protecting people.
 
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