Bonding jumper at first disconnect

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Davebones

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Have a 400 amp disconnect that has small bus bar that jumpers to the frame with a green ground screw from the neutral terminal . ( System Bonding Jumper ) The grounding electrode conductor to building steel is also tied to the neutral lug . There is a ground lug on the bottom of the cabinet that the equipment grounding conductors tie-in to . Engineer says that because drawings show what looks like a wiring that goes directly to the ground bar ( System Bonding Jumper ) there needs to be a wire to the ground bar . Its already grounded thru the cabinet and the existing system bonding jumper . Is this not correct as it is ?
 
I believe he is mistaken. Ground bars don't need a conductor to the neutral bar. If it was a neutral bar it would be a different story.
 
The engineer has one of the drawing's that show's how to ground a separately derived system . When you look at it it shows the system bonding jumper going to a ground terminal . I told him as long as the jumper is there it doesn't have to go directly to the ground bar .It's jumpered to the cabinet and the ground bar is attached to the cabinet .
 
Maybe he is refering to a "supply-side bonding jumper" (250.30 (A) (2) which you need if you flexed (likely) from the transformer to the disconnect. This is different than a "system bonding jumper".
Hopefully someone can post a good graphic.
 
texie said:
Maybe he is refering to a "supply-side bonding jumper" (250.30 (A) (2) which you need if you flexed (likely) from the transformer to the disconnect. This is different than a "system bonding jumper".
Hopefully someone can post a good graphic.
Click to expand...

Would you need a supply side bonding jumper if the neutral is grounded at the disconnect and not the transformer?
 
See 250.24.4 (2008)

At the service disconnect panel, if the GEC (Grounding Electrode Conductor) is connected to the ground bar, then a wire or busbar must be run to the neutral bus to complete the bonding. On larger installations, switchgear manufacturers provide a termination lug on the ground bar for terminating the UFER conductor. These panels will also usually have a neutral disconnect link and a busbar to the neutral bus. The idea is that you may not rely on the enclosure alone to bond the GEC and EGC conductors to the neutral bus. 250.24.B covers bonding of the EGC's, grounded conductor and enclosure.

In your case, the GEC being connected to the neutral bar with a green bonding screw installed meets code as is.
 
infinity said:
Would you need a supply side bonding jumper if the neutral is grounded at the disconnect and not the transformer?
Click to expand...

The way I'm reading the OP, I'm assuming the system bonding is being done at the disconnect, not the xformer, which creates the need for a supply-side bonding jumper.
 
meternerd said:
See 250.24.4 (2008)

At the service disconnect panel, if the GEC (Grounding Electrode Conductor) is connected to the ground bar, then a wire or busbar must be run to the neutral bus to complete the bonding. On larger installations, switchgear manufacturers provide a termination lug on the ground bar for terminating the UFER conductor. These panels will also usually have a neutral disconnect link and a busbar to the neutral bus. The idea is that you may not rely on the enclosure alone to bond the GEC and EGC conductors to the neutral bus. 250.24.B covers bonding of the EGC's, grounded conductor and enclosure.

In your case, the GEC being connected to the neutral bar with a green bonding screw installed meets code as is.
Click to expand...

Agreed, assuming there is a supply-side bonding jumper.
 
Too slow to edit...

Too slow to edit...

I found out there's a 15 minute limit on edits, so I'll post a new reply.

I think I was in error. According to 250.24 B the main bonding jumper must be unspliced and bond the neutral bus, enclosure and EGC's together. Looks to me like the solution is leave the green screw installed and to install a jumper from the ground bus where the EGC's are to the neutral bus. The other option is to move the EGC's to the neutral bus. If this isn't a service, then I'll leave the ansewr to others. I'm just a lowly utility electrician.
 
This is a transformer 75 kva 480V to 120-208v system added in plant . The bonding of the neutral is being done at the first disconnect . The green ground screw bonds the neutral to the cabinet in the center of the disconnect . The ground lug is at the bottom of the cabinet . The drawing he's got shows a connection between neutral bar and ground bar . I'm saying the bonding jumper ( green ground screw ) is that connection . He's saying there should be a wire from neurtal lug terminal to ground lug terminal .
 
Davebones said:
This is a transformer 75 kva 480V to 120-208v system added in plant . The bonding of the neutral is being done at the first disconnect . The green ground screw bonds the neutral to the cabinet in the center of the disconnect . The ground lug is at the bottom of the cabinet . The drawing he's got shows a connection between neutral bar and ground bar . I'm saying the bonding jumper ( green ground screw ) is that connection . He's saying there should be a wire from neurtal lug terminal to ground lug terminal .
Click to expand...

This is one of those situations where politics maybe should rule over technically right.
  1. If the engineer designed the installation, he is technically an Authority having jurisdiction and has the ability to demand the jumper wire.
  2. The wire offers a better ground than the screw, and in the situation that you describe, I would probably want a to install a jumper wire too.
  3. Why would you want to alienate him?
 
Not trying to aleniate the engineer will install the jumper . Just have not had a problem with this type of grounding setup before . The drawing he's showing is out of the 2011 NFPA Handbook ( Exhibit 250.14 ) . He points to " System Bonding Jumper " which show's it going to " G " lug .
 
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