system bonding jumper

[AKsparky1]

I would like to know where in article 250 does it say that a panel enclosure can carry a ground fault current to the neutral so the fault current can get back to the source winding to trip the ocpd? Example: I have a separately derived system (transformer) where the case is connected to the gec. Only. The xo is floated. The panel which is the first disconnecting means has a neutral to case connection (a wire sized correctly). The egc is connected via bus bar to the gec. If there is a line side groundfault then it has to travel on the gec then travel on the can to get back to the source. It seams to me that the can is the system bonding jumper because it connects the system grounded conductor to the egc and the gec.

 

[GoldDigger]

If the X0 is floated, how can current get back to it via the case?
Or do you mean that the neutral is connected to the X0 but not bonded to EGC at the transformer?

 

[infinity]

The GEC should connect to the neutral at the same point as the system bonding jumper.

 

[Smart $]

The GEC should connect to the neutral at the same point as the system bonding jumper.

Ditto... GEC and SBJ connections are required to be in the same enclosure... but exception permits connecting GEC to grounding bus rather than neutral.

 

[AKsparky1]

If the X0 is floated, how can current get back to it via the case?
Or do you mean that the neutral is connected to the X0 but not bonded to EGC at the transformer?

The panel enclosure is connected to the same GEC that the xfmr is connected to. I was just wondering if the can is rated for use as service equipment then can it be used to carry the fault current or does the jumper from the neutral in the panel to the panel enclosure have to be landed at the ground bar (same point). When you read the definition of system bonding jumper it seems like in my case the can is part of that definition because it is the only thing connecting the GEC, EGC, and the grounded conductor together.

 

[ActionDave]

I would like to know where in article 250 does it say that a panel enclosure can carry a ground fault current to the neutral so the fault current can get back to the source winding to trip the ocpd?

If I understand your question the answer is; there is no where in art. 250 that really says as much, it is just accepted.

Example: I have a separately derived system (transformer) where the case is connected to the gec. Only. The xo is floated. The panel which is the first disconnecting means has a neutral to case connection (a wire sized correctly).

If the XO is floated at the transformer then the case of the transformer should be connected to an Equipment Grounding Conductor included with the primary feed.

The egc is connected via bus bar to the gec. If there is a line side groundfault then it has to travel on the gec then travel on the can to get back to the source. It seams to me that the can is the system bonding jumper because it connects the system grounded conductor to the egc and the gec.

Getting fuzzy here. The secondary GEC, usually a connection to the building steel, has to land wherever the XO is bonded. The XO of a transformer as an SDS can be bonded at the transformer or at the first disconnect. I learned to do it at the first disconnect and that is what I do.

 

[Smart $]

The panel enclosure is connected to the same GEC that the xfmr is connected to. I was just wondering if the can is rated for use as service equipment then can it be used to carry the fault current or does the jumper from the neutral in the panel to the panel enclosure have to be landed at the ground bar (same point). When you read the definition of system bonding jumper it seems like in my case the can is part of that definition because it is the only thing connecting the GEC, EGC, and the grounded conductor together.

If I understand your description correctly, the SBJ must be properly-sized wire or bus to connect the GEC to the EG in same enclosure as SBJ. If not, the GEC must connect to the grounded conductor at the same point as the SBJ. BTW, the "can" is not a bus under Code. See 250.3(A)(5) and Exception No. 1 thereto.

Are you certain what you are calling the GEC to transformer case is not instead the supply-side bonding jumper (SSBJ)???

 

[AKsparky1]

Potos

 

[AKsparky1]

The question is does the coductor from the neutral bar to the can meet code or does the connection have to be made at the same point the GECand EGC is connected?

 

[Smart $]

The question is does the coductor from the neutral bar to the can meet code or does the connection have to be made at the same point the GECand EGC is connected?

The wire jumper has to connect the grounded conductor to the EGB (i.e. busbar). The installation as pictured is non-compliant.

 

[AKsparky1]

The wire jumper has to connect the grounded conductor to the EGB (i.e. busbar). The installation as pictured is non-compliant.

Thank you for the feedback and I do appolagize for the photo not being right side up. I would like to tell you that the authority is allowing this to stay the same. I use this site for educational purposes only and will not push the isue with my employer. I hope that you did notice the black wire with 3 white stripes at the bottom of the neutral bar that lands at the top of the panel enclosure via bolt.

I am also aware that in residential when a service bond is made in a panel (first disconnecting means) rather then in the meter base or source, that the green screw is the system bonding jumper and a line side ground fault would have to travel on the panel enclosure to get to the neutral. I just cannot seem to find where this is permitted in 250 but I would only be comfortable doing this in a small pannel but not one this size. maybe when the panel is rated for use as service equipment then that means it has been tested to carry a large fault current on the enclosure. It should be bonded to building steel YES (oil feild specification all metal structure) but not serve as the only means for the fault current path. screws and the like would be fried! would you agree?

 

[ActionDave]

Thank you for the feedback and I do appolagize for the photo not being right side up. I would like to tell you that the authority is allowing this to stay the same. I use this site for educational purposes only and will not push the isue with my employer. I hope that you did notice the black wire with 3 white stripes at the bottom of the neutral bar that lands at the top of the panel enclosure via bolt.

I am also aware that in residential when a service bond is made in a panel (first disconnecting means) rather then in the meter base or source, that the green screw is the system bonding jumper and a line side ground fault would have to travel on the panel enclosure to get to the neutral. I just cannot seem to find where this is permitted in 250 but I would only be comfortable doing this in a small pannel but not one this size. maybe when the panel is rated for use as service equipment then that means it has been tested to carry a large fault current on the enclosure. It should be bonded to building steel YES (oil feild specification all metal structure) but not serve as the only means for the fault current path. screws and the like would be fried! would you agree?

The neutral is bonded to the panel with a screw at some point unless you want to cadweld it in there. Industrial panel or resi panel makes no matter.

The NEC does not directly say that you can use the panel/steel that it is made of, as way to land all your EGC's separate from the neutrals, but you are allowed. It has been done for seventy five years at least.