High Resistive Ground (HRG)

stephena

Member
Location
oregon
There is a utility Xformer and we have 8 sets of 500kcmil conductors to the service disconnect about 50' away. The HRG is located by the Xformer and it has a 8AWG neutral to the Xformer XO terminal and from the load side of the resister a green wire (factory sized) to a grounding bar. From the grounding bar we bonded the Xformer casing. We didn't pull any supply side bonding jumpers with the service conductors to the service equipment. Isn't this a violation? Doesn't there need to be a connection from the Xformer case to the service equipment enclosure? If a fault took place in the Xformer on one phase then the service equipment on another phase then the earth would be the only thing between the two enclosures conducting the fault current to trip the OCP. The 500s were installed in PVC by the way
 

Smart $

Esteemed Member
Location
Ohio
250.36
(E) Equipment Bonding Jumper. The equipment bonding
jumper (the connection between the equipment grounding
conductors and the grounding impedance) shall be an
unspliced conductor run from the first system disconnecting
means or overcurrent device to the grounded side of the
grounding impedance.
 

stephena

Member
Location
oregon
I understand that part but what about supply side bonding between the Xformer casing and Switchgear? 250.36 says high impedence grounding systems shall comply with 250.36 A-G. They don't mention anything about supplyside bonding jumpers and without those if a fault takes place in the Xformer on one phase and a second fault on another phase in the switchgear the ground is going to be carrying the phase to phase fault to trip the breaker
 

Smart $

Esteemed Member
Location
Ohio
I understand that part but what about supply side bonding between the Xformer casing and Switchgear?
That's what the EBJ does. It bonds the equipment ground at the service disconnect to the grounded side of the grounding impedance... which is bonded to the transformer case.

In this case EBJ = SSBJ. This particular Code section has not been "technically correlated" to 250.102 since Code started using the term Supply-Side Bonding Jumper in the 2011 edition.

250.36 says high impedence grounding systems shall comply with 250.36 A-G. They don't mention anything about supplyside bonding jumpers and without those if a fault takes place in the Xformer on one phase and a second fault on another phase in the switchgear the ground is going to be carrying the phase to phase fault to trip the breaker
I assume by ground, you meant the dirt kind. Installing the EBJ will remedy that... well at least the majority of it.

Where are your ground detector "sensors" located. Please be specific.
 

stephena

Member
Location
oregon
Yes ground as in earth. The HRG is in a separate enclosure about 5' away from the Xformer and the Switchgear is about 50' away from the Xformer. The conduits connecting everything is PVC there is no equipment or supplyside bonding jumper connecting the Xformer case to the Switchgear. The only bonding wire is the equipment bonding jumper from the HRG to the Switchgear. I think this is wrong because like I said what happens if there is a fault in Xformer on one phase and another in Switchgear on a second phase? Then the earth is going to carry the fault current and 250.4B4 or 5 says the earth can't conduct fault current. But reading over 250.36 I don't see anything stating that we must have supply side bonding jumpers and if so that parallel runs need to have the supply side bonding jumper paralleled as 250.102 requires.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Yes ground as in earth. The HRG is in a separate enclosure about 5' away from the Xformer and the Switchgear is about 50' away from the Xformer. The conduits connecting everything is PVC there is no equipment or supplyside bonding jumper connecting the Xformer case to the Switchgear. The only bonding wire is the equipment bonding jumper from the HRG to the Switchgear. I think this is wrong because like I said what happens if there is a fault in Xformer on one phase and another in Switchgear on a second phase? Then the earth is going to carry the fault current and 250.4B4 or 5 says the earth can't conduct fault current. But reading over 250.36 I don't see anything stating that we must have supply side bonding jumpers and if so that parallel runs need to have the supply side bonding jumper paralleled as 250.102 requires.
But I don't see anything in 250.36 that says you don't or that the other rules in 250 do not apply.
 
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