NEC 250.102(C)(1) question

[curious101]

Hello,

Can you please tell if in the attached snapshot, the red feeder sizes are correct and the bare minimum per code?
600A service, no single main service disconnect. Grounding electrode in wireway per NEC 250.64(D)(3).
Aluminum used. From wireway downstream into (1) 125A fused disconnect and (2) 225A fused disconnects.

Thank you!

 

[augie47]

I believe for your parallel 500s you could use a 4/0 AL

 

[curious101]

This is where I would need a bit of explanation. Note 3 under table 250.102(c)(1) says that for parallel sets the largest ungrounded supply conductors is determined by the the largest sum of the areas of the corresponding conductors of each set. That would be 4x500=2000 kcmil, right? So that puts me into the over 1750 kcmil Aluminum in size of largest ungrounded conductor in the table and that points me to notes 1 and 2 for the size of grounded conductor. Note 1 says that the grounded conductor shall have an area not less than 12.5% the largest ungrounded supply conductor (which is 2000 kcmil in my case). 12.5% of 2000 kcmil is 250 kcmil. Am I off or is there an exception that I'm missing? Thank you in advance for the explanation!

 

[wwhitney]

This is where I would need a bit of explanation. Note 3 under table 250.102(c)(1) says that for parallel sets the largest ungrounded supply conductors is determined by the the largest sum of the areas of the corresponding conductors of each set. That would be 4x500=2000 kcmil, right?

No, for 2 sets of 500 kcmil, that's 2x500 = 1000.

Cheers, Wayne

 

[infinity]

What is the SSBJ for are these metal raceways? If so they only require bonding at one end.

 

[curious101]

No, for 2 sets of 500 kcmil, that's 2x500 = 1000.

Cheers, Wayne

Thank you for your input! My question is, when I look at the 2014 NEC handbook on page 177, it lists this application example:

So, it's looking at the cross section of one of the (3) parallel phases. In my case, in one of the (2) sets, I have (4) 500 kcmil, so it's 4x500=2000.
12.5% of that is 250kcmil.
I guess, If I decide to use (3) 500kcmil and (1) 4/0 for the neutral, that would give me a total of 3x500+211.6=1711.6 kcmil, and that would actually put me (in Aluminum) into the Over 900 through 1750 category and qualify for the 4/0 supply side bonding jumper.
Do you see where I'm coming from?

 

[infinity]

So, it's looking at the cross section of one of the (3) parallel phases. In my case, in one of the (2) sets, I have (4) 500 kcmil, so it's 4x500=2000.
12.5% of that is 250kcmil.
I guess, If I decide to use (3) 500kcmil and (1) 4/0 for the neutral, that would give me a total of 3x500+211.6=1711.6 kcmil, and that would actually put me (in Aluminum) into the Over 900 through 1750 category and qualify for the 4/0 supply side bonding jumper.
Do you see where I'm coming from?

If you have two sets of 500's that's 1000 kcmil not 2000. If you have 3 sets of 500's that's 1500 kcmil. You do not add in the neutral into the mix.

 

[augie47]

The drawing only shows 2 sets of 500s..... it's figured on # of wires per phase....in your case = 2 X 500

 

[curious101]

What is the SSBJ for are these metal raceways? If so they only require bonding at one end.

Thank you! Sorry to bother!
In this handbook example picture (for practice), it shows bonding on supply side and on the load side too:

 

[curious101]

If you have two sets of 500's that's 1000 kcmil not 2000. If you have 3 sets of 500's that's 1500 kcmil. You do not add in the neutral into the mix.

Thank you!
Sorry, the previous handbook application example threw me off normal thinking because of my own fault.
Sorry to bother and take up your time!

 

[curious101]

The drawing only shows 2 sets of 500s..... it's figured on # of wires per phase....in your case = 2 X 500

Thank you!
Sorry, the previous handbook application example threw me off normal thinking because of my own fault.
Sorry to bother and take up your time!

 

[augie47]

No apology... that's why we are here

 

[infinity]

Thank you! Sorry to bother!

No need to apologize you're not bothering anyone. We're all here to learn and share knowledge so if you don't understand something feel free to ask.

 

[infinity]

In this handbook example picture (for practice), it shows bonding on supply side and on the load side too:

My question was regarding what kind of raceways are being used. All metal raceways that contain service conductors require bonding beyond standard locknuts. And all of the service raceways that require bonding only require it on one end as shown in your graphic in post #9.

 

[curious101]

My question was regarding what kind of raceways are being used. All metal raceways that contain service conductors require bonding beyond standard locknuts. And all of the service raceways that require bonding only require it on one end as shown in your graphic in post #9.

Thank you!
More questions from me (I can't believe I'm still trying to clarify stuff that is so obvious to all).
1. If we have metal raceway, what does the bonding beyond standard locknuts entail?
2. As far as the options how the service can be bonded: the service bonding size is always determined based upon the service supply side ungrounded conductors (as opposed to the individual load side disconnect ungrounded conductors)? And whatever we determined from the service supply side, can be shown either on the supply or the load side? In other words, which ones of the (3) below options are correct?
Thank you!

 

[augie47]

Option 2 comes closest.,
If you are using PVC conduits I would assure the CT cabinet was bonded to the neutral, bond my wireway to the neutral and connect m,y GEC to that terminal, install your 4/0 bonding jumper to bond the j box and bond my disconnects by the MBJ to the neutral.
With PVC no other bonding jumpers are needed,



250.92 states that metallic service raceways must be bonded and the "standard locknuts and bushings shall not be the only means"
The CT cabinet is normally bonded by connecting the cabinet to the neutral conductor.
The j box and wireway can be bonded by connection to the neutrals, or by connection to the bonding jumper you show, or my the use of grounding type lockouts (if no concentric or eccentric ko's are present).
Likewise the conduits can be bonded using bonding locknuts or bushings.

Were I to install it without specifications I would go PVC. If I had to use metal conduit, . I likely would not worry about bonding jumpers but would assure the CT cabinet is connected to the neutrals and I would use grounding locknuts or bushings on each conduit to bond them and bond my neutral in the wireway and connect my GEC to that terminal also (as shown).
Others might do it differently but the end result would be all metallic raceways, boxes, and wireways containing service conductors be bonded by proper locknuts or bushings or by proper sized jumpers.
Your disconnects would have MBJ (assuming there is no service disconnect ahead of these) so they would be bonded and the grounding locknut or bushing on the supply conduit would bond those conduits,.
If you had eccentric knockouts bond bushing would be required instead of locknuts and you would use jumpers sized as shown on your drawing tp connect those bushings to the neutral terminals.

 

[curious101]

Option 2 comes closest.,
If you are using PVC conduits I would assure the CT cabinet was bonded to the neutral, bond my wireway to the neutral and connect m,y GEC to that terminal, install your 4/0 bonding jumper to bond the j box and bond my disconnects by the MBJ to the neutral.
With PVC no other bonding jumpers are needed,



250.92 states that metallic service raceways must be bonded and the "standard locknuts and bushings shall not be the only means"
The CT cabinet is normally bonded by connecting the cabinet to the neutral conductor.
The j box and wireway can be bonded by connection to the neutrals, or by connection to the bonding jumper you show, or my the use of grounding type lockouts (if no concentric or eccentric ko's are present).
Likewise the conduits can be bonded using bonding locknuts or bushings.

Were I to install it without specifications I would go PVC. If I had to use metal conduit, . I likely would not worry about bonding jumpers but would assure the CT cabinet is connected to the neutrals and I would use grounding locknuts or bushings on each conduit to bond them and bond my neutral in the wireway and connect my GEC to that terminal also (as shown).
Others might do it differently but the end result would be all metallic raceways, boxes, and wireways containing service conductors be bonded by proper locknuts or bushings or by proper sized jumpers.
Your disconnects would have MBJ (assuming there is no service disconnect ahead of these) so they would be bonded and the grounding locknut or bushing on the supply conduit would bond those conduits,.
If you had eccentric knockouts bond bushing would be required instead of locknuts and you would use jumpers sized as shown on your drawing tp connect those bushings to the neutral terminals.

Thank you! I have to study this…. Will come back if I have questions….

 

[curious101]

Question regarding the diagram in post #9 above. Is there supposed to be an equipment grounding bus in the enclosed circuit breakers? Where are the equipment ground wires from downstream loads supposed to terminate? If there are isolated ground loads downstream one of the enclosed circuit breakers, where is the isolated ground supposed to terminate? Thank you!

 

[augie47]

Load side equipment grounding conductors can land on the neutral bar is any service equipment or on a ground bar attached to the enclosure or to the enclosure itself. The main bonding jumper connects the neutral to the enclosure and ground bars so you have a path back to the neutral and source.

 

[curious101]

Load side equipment grounding conductors can land on the neutral bar is any service equipment or on a ground bar attached to the enclosure or to the enclosure itself. The main bonding jumper connects the neutral to the enclosure and ground bars so you have a path back to the neutral and source.

Thank you!