Classifying and Sizing a Grounding Conductor

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KD8HE

KD8HE

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West Virginia
Checking an existing system and trying to decide whether to apply 250.66 or 250.122 to verify size of a grounding conductor?
Given, an industrial system, 1500 KVA pad mounted transformer, 480v, Y secondary, no neutral loads, no grounded conductor.This grounding conductor runs between two ground electrode systems, one ring at the transformer and one ring at the MCC. It is also connected to the grounding lug of the transformer and the MCC ground buss. Is it a grounding electrode conductor or an equipment grounding conductor? Here's the kicker...It is in the same conduit that encloses the transformer secondary conductors that feed the MCC main breaker (considered the service equipment in this case).
1. What do we call it?
2. if 250.122 applies to it's sizing and the transformer is not fused on the secondary, what do we use to size the conductor?
Appreciate any comments?
:?HE
 
As a clarification...the conductor runs from the transformer electrode system to the transformer grounding lug then through the MCC feeder raceway to the MCC ground buss and then to the MCC electrode system. It is not a continuous cable but lugged and bolted at each grounding connection point on the transformer and MCC.
 
Welcome to the Forum
You sure picked a doozey for your first post :D

As I read, I find I have more questions than answers.... :D

You state a 480Y secondary but you have no grounded conductors. Is the XO terminal connected or bonded to anything ?
(If not it seems it's being treated as a ungrounded system)

The ground rings do not appear they would comply with 250.30(A)(7)

The conductor you describe appears to be more the bonding means between the transformer and the MCC and would be the path of any fault current back to the transformer. As such, the supply conductors are ahead of any OCP device so it would need to be sized per 250.66.

Is there another ground path between the MCC and the transformer ?
 
augie47 said:
Welcome to the Forum
You sure picked a doozey for your first post :D <<work in the coal mining industry...see all sort of interesting applications of electrical equipment>>

As I read, I find I have more questions than answers.... :D <<expected>>

You state a 480Y secondary but you have no grounded conductors. Is the XO terminal connected or bonded to anything ?
(If not it seems it's being treated as a ungrounded system). <<resistance grounded XO>>

The ground rings do not appear they would comply with 250.30(A)(7) <<how does this apply to the "rings"? Leads to 250.64 (A)(B)(C) and (E) which relates to ground electrode conductor installation. As nooted this conductor is not continuous but does use listed connectors to make connection to the transformer and MCC ground connections>>

The conductor you describe appears to be more the bonding means between the transformer and the MCC and would be the path of any fault current back to the transformer. As such, the supply conductors are ahead of any OCP device so it would need to be sized per 250.66. <<my inclination also, supply conductors are 500s, grounding conductor is 2/0, adequately sized i think confusing as to application since it is in the same raceway as the supply conductors to the MCC>>

Is there another ground path between the MCC and the transformer ?
Click to expand...
<<no>>
 
augie47 said:
??

No...... XO is not connected to anything ?
No...... there is no ground path (other than the wire you question) between MCC and Transf. ?
Click to expand...

Given the OP's description, there is no fault current path without that bonding jumper. As you mentioned I believe we have an ungrounded system here.:(
 
Assuming we are correct, would 110.3(B) not dictate that a grounding method be a part of the phase conductor routing ?
In which case the conductor he questions would be an auxiliary grounding electrode conductor.
 
chris kennedy said:
Given the OP's description, there is no fault current path without that bonding jumper. As you mentioned I believe we have an ungrounded system here.:(
Click to expand...

X0 is high resistance grounded
No other ground path between tx and mcc except the conductor of interest.
Fault current path is to ground to X0 through resistor.
 
In that case I can only reference 250.36 and quietly bow out to those far more familiar with this type system. I have never had any experience installing or inspecting one.
 
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