Sizing system bonding jumper

[Shockedby277v]

I may have not worded it correctly but my gear came without a system bonding jumper between my neutral and grounding system busses. Typically it is a piece of bussing. My transformer is 12470 to 480/277 Indoors and all one section with the primary switch => transformer => service section => distribution. My secondaries are busses. How do I size my bonding jumpers on a 480/277 volt 2500 amp system?
I was told 250.102

 

[Shockedby277v]

250.28 looks like the article I need? Looks like a 3/0 copper would work?

 

[drcampbell]

Just a wild guess here, but if you're installing something that big, you're following a formal print prepared & sealed by a registered professional engineer? Ask the person who prepared it.

 

[infinity]

Are you saying that there is no secondary OCPD? Normally the SBJ is sized based on the secondary conductors and T250.102(C)(1). Since you have bus that's an interesting question. If you used an equivalent conductor size say 600 kcmil copper you would need 6 sets which is 3600 kcmil*12.5% =450 kcmil.

 

[texie]

There must be more to this story. Something like this should already have a factory bonding jumper that is bussed. Also this would have GFPE so it's not like just go and add a jumper of your own.

 

[jap]

I may have not worded it correctly but my gear came without a system bonding jumper between my neutral and grounding system busses. Typically it is a piece of bussing. My transformer is 12470 to 480/277 Indoors and all one section with the primary switch => transformer => service section => distribution. My secondaries are busses. How do I size my bonding jumpers on a 480/277 volt 2500 amp system?
I was told 250.102

Seems odd you don't have a factory bonding jumper located somewhere on the secondary buss bars in the service section.

I'd contact the gear provider before I'd make my own.

JAP>

 

[ActionDave]

Had the same thing happen to me last year. Went round and round with the sales rep. Finally got through to a factory rep. They sent me a foot long piece of wire and a lug.

 

[ActionDave]

250.102 is the table it would be sized sized with.

 

[Strathead]

I may have not worded it correctly but my gear came without a system bonding jumper between my neutral and grounding system busses. Typically it is a piece of bussing. My transformer is 12470 to 480/277 Indoors and all one section with the primary switch => transformer => service section => distribution. My secondaries are busses. How do I size my bonding jumpers on a 480/277 volt 2500 amp system?
I was told 250.102

So, the transformer is customer owned, that is why you used the term system bonding jumper correct? T250.102 is the correct table. As Infinity stated, you or the manufacturer sizes it per the conductor size. Note 1 tells you how it is sized. for the area of the bus it is the thickness times the width.

 

[jap]

I'm curious if the transformer has an XO strap to the frame.


JAP>

 

[Shockedby277v]

There must be more to this story. Something like this should already have a factory bonding jumper that is bussed. Also this would have GFPE so it's not like just go and add a jumper of your own.

I have been doing electrical for 22 years and running large work for 18 years and this is the absolute worse experience I have had with this manufacturer. It is slowly being resolved and if anything we will need to provide a temporary jumper until they come to complete this mess. They were missing bussing between the transformer to service as well as the neutral bussing between my 2 service distributions and center tie breaker section. I think we will have a solid plan by Tuesday when it is time to fire this up. I have never had to deal with installing a jumper before because the bussing handles it all, jumper included.

 

[Shockedby277v]

I'm curious if the transformer has an XO strap to the frame.


JAP>

Negative. There is no continuity between XO and ground currently.

 

[infinity]

It is slowly being resolved and if anything we will need to provide a temporary jumper until they come to complete this mess

I would fixure out the size conductors required for 2500 amps and use that to size the SBJ.

 

[ActionDave]

Was it from Eaton?

 

[Strathead]

I would fixure out the size conductors required for 2500 amps and use that to size the SBJ.

But as you wrote previously, T250.102 tells him how to figure the size and your suggestion isn't it. As I stated, bus width times bus height gives the area, then chapter nine tables to find a conductor/s that have the equivalent area. Conductor size is based on the size of the conductors, not the amperage of the overcurrent protection.

 

[jap]

But as you wrote previously, T250.102 tells him how to figure the size and your suggestion isn't it. As I stated, bus width times bus height gives the area, then chapter nine tables to find a conductor/s that have the equivalent area. Conductor size is based on the size of the conductors, not the amperage of the overcurrent protection.

So the thickness of the bussing makes no difference?
Only width times buss height?


JAP>

 

[jap]

But as you wrote previously, T250.102 tells him how to figure the size and your suggestion isn't it. As I stated, bus width times bus height gives the area, then chapter nine tables to find a conductor/s that have the equivalent area. Conductor size is based on the size of the conductors, not the amperage of the overcurrent protection.

In post #9 you said it was the "thickness times the width"
In post #15 you said it was the "width times the height".
See how easy it would be to size things off of miscommunication?

This is not up to him to figure this out.

This is a manufactured piece of equipment that should come with a factory bonding jumper.

You either get that factory bonding jumper from the manufacturer and install it, or, get documentation of what size and type of bonding jumper they suggest you install in their piece of equipment.

If not, you've needlessly assumed responsibility for their piece of equipment should something go south and your calculations happen to be incorrect.

JAP>

 

[LarryFine]

So the thickness of the bussing makes no difference?
Only width times buss height?

Cross-section area. Use whichever two terms you prefer.

Yes, if you're looking at one end of the bus, width x height.

 

[jap]

Cross-section area. Use whichever two terms you prefer.

Yes, if you're looking at one end of the bus, width x height.

And if I'm looking at the face of it, width x height is not going to tell me how thick it is.

Cross sectional has to be mentioned somehow.

JAP>

 

[Strathead]

Cross-section area. Use whichever two terms you prefer.

Yes, if you're looking at one end of the bus, width x height.

In post #9 you said it was the "thickness times the width"
In post #15 you said it was the "width times the height".

They both mean the same thing. This is splitting hairs, but also why I changed the term I used, since with a fresh brain I realized that width time height was a more accurate description. The only other dimension is length (unless you are smoking good ganja) and none of those terms can easily be confused as the length.