Bonding confusion for conduits and enclosures and utter disappointment.

[ChillSparky]

Details:
600A Service
500 MCM AL parallel

We have read read read, and re-read the handbook, two different study books and even looked online. We are still lost on how to properly bond all our conduit and enclosures on our this 600A service. We have a 600A CT on the main floor, the rest of our service is in the basement directly below it. We have installed the MBJ in our 600A Main Disconnect. Directly to the left of that service disconnect we have a gutter that feeds 1 200A fused disconnect for 1-200A panelboard, 1-200A fused at 150A to feed an RTU and 1-100A disconnect to feed an air handler. These all are fed from the feeders that are in the gutter. We have ground bushings on every side of every conduit.
Questions:
? Do we have to use one wire to bond all these bushings, and does that wire go back to the 600A disconnect?
? Can we use #1 CU to set a terminal bar inside the gutter to tap off for each disconnect after the 600A, using #6 CU? If so does this have to be a floating bar?
? Can we just jumper/bond each conduit to the respecting enclosure and call it good? Or does the bonding wire have to run through each conduit?
? Should we plan to set a grounding terminal inside the 600A, use a separate conduit and send our bonds and grounds each separately for their respective disconnects and enclosures?
I feel like I should know this without incident and feel really stupid for getting so confused and lost on this particular issue. Any help and guidance would be greatly appreciated. Sometimes one can think they understand something, then they look in the code book and then find out that they don?t and end up in a loop, searching for the correct answer. Thanks again!

 

[texie]

Details:
600A Service
500 MCM AL parallel

We have read read read, and re-read the handbook, two different study books and even looked online. We are still lost on how to properly bond all our conduit and enclosures on our this 600A service. We have a 600A CT on the main floor, the rest of our service is in the basement directly below it. We have installed the MBJ in our 600A Main Disconnect. Directly to the left of that service disconnect we have a gutter that feeds 1 200A fused disconnect for 1-200A panelboard, 1-200A fused at 150A to feed an RTU and 1-100A disconnect to feed an air handler. These all are fed from the feeders that are in the gutter. We have ground bushings on every side of every conduit.
Questions:
? Do we have to use one wire to bond all these bushings, and does that wire go back to the 600A disconnect?
? Can we use #1 CU to set a terminal bar inside the gutter to tap off for each disconnect after the 600A, using #6 CU? If so does this have to be a floating bar?
? Can we just jumper/bond each conduit to the respecting enclosure and call it good? Or does the bonding wire have to run through each conduit?
? Should we plan to set a grounding terminal inside the 600A, use a separate conduit and send our bonds and grounds each separately for their respective disconnects and enclosures?
I feel like I should know this without incident and feel really stupid for getting so confused and lost on this particular issue. Any help and guidance would be greatly appreciated. Sometimes one can think they understand something, then they look in the code book and then find out that they don’t and end up in a loop, searching for the correct answer. Thanks again!

You bond the neutral in the 600 amp disco as you did. The other 3 discos are not service equipment as they are down stream of the main disco so you leave those neutrals unbonded. The grounding bushings are optional downstream of the main in your case. If you want you can use them and just jumper them at one end to the enclosure with a jumper sized per Table 250.122 (see also 250.122- but it won't apply in this case I don't think). Make sure the neutral is bonded in the CT can (not all are factory bonded). You didn't mention the type of raceway for the service conductors to the 600 amp switch -that may be another subject.

 

[augie47]

It appears your system is 240 (or 208) volt based on the loadcener (if not the answer below will vary somewhat)
With that in mind, barring any loose fitting wireways, your conduits handle the necessary bonding on the load side of your service disconnect without any bonding bushings, lockouts or jumpers.

That said, if you wish to use bonding bushings, since you are on the load side of your 600 amp disconnect, and bonding prior to a downstream over-current device would be based on the 600 amp fuse and be sized at #1.
Bonding can be accomplished with a single #1 to all bushings or separate #1s to each bushing back to a common point.

(typing as texie posted)

 

[texie]

I might add-did you do the calcs to be certain that gutter is large enough for all those conductors and splices? Hard to tell in the photo but it looks questionable. Is the POCO OK with the service disco inside the building (not all are, regardless of the NEC)?

 

[ChillSparky]

You bond the neutral in the 600 amp disco as you did. The other 3 discos are not service equipment as they are down stream of the main disco so you leave those neutrals unbonded. The grounding bushings are optional downstream of the main in your case. If you want you can use them and just jumper them at one end to the enclosure with a jumper sized per Table 250.122 (see also 250.122- but it won't apply in this case I don't think). Make sure the neutral is bonded in the CT can (not all are factory bonded). You didn't mention the type of raceway for the service conductors to the 600 amp switch -that may be another subject.

We have 3 1/2 inch EMT between the CT and the Main. GRC up from the CT. I realize I will have to provide supply side jumpers, but do I have to as well inside the CT?
Calcs were done and it is within.

 

[texie]

We have 3 1/2 inch EMT between the CT and the Main. GRC up from the CT. I realize I will have to provide supply side jumpers, but do I have to as well inside the CT?
Calcs were done and it is within.

Since you are using EMT you will need a bonding bushing at the CT end if the neutral is not bonded in the CT cabinet. Some CT cans do not have a bonded neutral. Other wise you could just use one bonding bushing on the other end. Of course the GRC from the POCO needs bonding as well.

 

[ChillSparky]

Thanks alot guys. I feel a little better now. I felt like I was over-analyzing this, I will post inspection results on Monday! I appreciate it tons! Hopefully one day I can answer some questions for people too!

 

[texie]

Thanks alot guys. I feel a little better now. I felt like I was over-analyzing this, I will post inspection results on Monday! I appreciate it tons! Hopefully one day I can answer some questions for people too!

Keep in mind that the bonding jumpers on the line side of the main must be sized per Table 250.66. If you use a separate jumper for each raceway you can size it for just the largest conductor in the raceway (500 AL). But if you daisy chain it from the enclosure to bushing to bushing you will need to size it for the total area of the conductors (1000 kcmil AL). In this case I would do separate jumpers so you can use #2 CU instead of 2/0 Cu. See Art. 250.102(C)(2).

 

[augie47]

If it was going to be inspected locally, as far as bonding, I would be looking for hubs, bonding bushings or grounding locknuts (if no eccentric/concentric knockouts) on the service conduits (if metallic) into the CT, a bonding jumper to the CT cabinet and bonding of one end of the service conduit from the CT to your main (same as supply side to CT) , and your main disconnect bind jumper.

 

[Strathead]

It appears your system is 240 (or 208) volt based on the loadcener (if not the answer below will vary somewhat)
With that in mind, barring any loose fitting wireways, your conduits handle the necessary bonding on the load side of your service disconnect without any bonding bushings, lockouts or jumpers.

That said, if you wish to use bonding bushings, since you are on the load side of your 600 amp disconnect, and bonding prior to a downstream over-current device would be based on the 600 amp fuse and be sized at #1.
Bonding can be accomplished with a single #1 to all bushings or separate #1s to each bushing back to a common point.

(typing as texie posted)

Augie, please correct me if I am reading this wrong. If I choose to put a ground bar inside the gutter and run grounds to separate ground bushings, I would only need to size each ground per 250.122 for the conductors in that raceway. So the 200A disconnect in this example would only need a #6 jumper and a #6 ground in the conduit also, and the only bushings that would require a #1 wire would be the bushings from the main disconnect. This is the way I always understood it so, either I am wrong, I am misreading what you wrote, or you miswrote. Please let me know?

 

[augie47]

Augie, please correct me if I am reading this wrong. If I choose to put a ground bar inside the gutter and run grounds to separate ground bushings, I would only need to size each ground per 250.122 for the conductors in that raceway. So the 200A disconnect in this example would only need a #6 jumper and a #6 ground in the conduit also, and the only bushings that would require a #1 wire would be the bushings from the main disconnect. This is the way I always understood it so, either I am wrong, I am misreading what you wrote, or you miswrote. Please let me know?

The way I see it, any bonding on the load side of an overcurrent device would need to be sized per 250.122 based on the OCP size protecting the conductors. If taps are made in the gutter the tap conductors are still protected by the main OCP so the bond jumper would have to be sized accordingly (#1 for 600 amp) unless the tap is smaller than a #1 in which case the jumper would not have to exceed the tap conductor size.
It's odd, for if they were service conductors you do size the individual jumpers based on the conductor size in the raceway,

Could be mistaken...been up for 3 hours it's overdue... but that's my outlook.,

 

[Strathead]

The way I see it, any bonding on the load side of an overcurrent device would need to be sized per 250.122 based on the OCP size protecting the conductors. If taps are made in the gutter the tap conductors are still protected by the main OCP so the bond jumper would have to be sized accordingly (#1 for 600 amp) unless the tap is smaller than a #1 in which case the jumper would not have to exceed the tap conductor size.
It's odd, for if they were service conductors you do size the individual jumpers based on the conductor size in the raceway,

Could be mistaken...been up for 3 hours it's overdue... but that's my outlook.,

Now we have a discussion! If you are correct, then the wire going in to the conduit can be a #6, but I can't pass it through the bond bushing because it wouldn't be large enough for the other conductors in the box? I hope that you are misinterpreting. I won't be surprised though, if you are reading it correctly and I am wrong. This is one of the sections of the code that I completely disagree with. I have done and seen others also do in the past. Take a #6 and run it through the bushings period. I don't do this any more, because I know it was not legal. However, when the intent of this code section is to allow sufficient current to trip the supplying breaker, this section over does it. I don't have to even run a ground, or put a bonding bushing on the conduit, but if I do, then it needs to be huge. This same issue I have a problem with the code regarding parallel feeds. I really think they should write these sections allowing smaller grounds.

BTW, I do still interpret the code to imply that a bond jumper the size of the feeders is all that is required for each load side conduit of a tap. Other please????

 

[ChillSparky]

One last question about the CT cabinet. Do we ground the cabinet and if so do i send the ground parallel? For 600 amps i think a #1 would do the trick. Just checking before i buy wire and double barrel lugs.

 

[texie]

One last question about the CT cabinet. Do we ground the cabinet and if so do i send the ground parallel? For 600 amps i think a #1 would do the trick. Just checking before i buy wire and double barrel lugs.

You mention "send" the ground as in a separate EGC? On the line side of the service you don't use an EGC. Anything metallic on the line side that needs grounding is done by bonding to the neutral. See my post #8.

 

[MarineTech]

Chill, I was wondering if you could please tell me the type of fuse selected?

Also, from the description I just wanted to confirm the setup:

600A 208V 3 Phase Y, grounded service, with disconnect remote.

Mains, feeders and taps use the same wire tray.

Main Bonding Jumper (MBJ) at disconnect.

Grounding Electrode Conductor at can.

EMT using knockouts between service and disconnect, bushing bonding per 250.66.

Thanks

 

[augie47]

Now we have a discussion! If you are correct, then the wire going in to the conduit can be a #6, but I can't pass it through the bond bushing because it wouldn't be large enough for the other conductors in the box? I hope that you are misinterpreting. I won't be surprised though, if you are reading it correctly and I am wrong. This is one of the sections of the code that I completely disagree with. I have done and seen others also do in the past. Take a #6 and run it through the bushings period. I don't do this any more, because I know it was not legal. However, when the intent of this code section is to allow sufficient current to trip the supplying breaker, this section over does it. I don't have to even run a ground, or put a bonding bushing on the conduit, but if I do, then it needs to be huge. This same issue I have a problem with the code regarding parallel feeds. I really think they should write these sections allowing smaller grounds.

BTW, I do still interpret the code to imply that a bond jumper the size of the feeders is all that is required for each load side conduit of a tap. Other please????

Note that I did say the bond jumper would not have to be larger than the phase conductor. I can find wording in 250.122 to support that, I can not find wording to support sizing it by the device at the end of the tap (ie: a #6 for a tap feeding a 200 amp switch).
In the case of a 100 amp panel, if we tap with a set of #3s and there is a line to conduit fault, the most current that could flow would be what the #3s could carry so a #3 bond jumper would be sufficient. If however the 3/0s to the 200 amp faulted in the supply conduit, the current flow, since it is on the line side of the 200 amp fuse, would not be limited to that covered by table 250.122 for a 200 amp feeder. 250.122 tells us a #1 bond is sufficient for the 600 amp
Without serious engineering data, we don't know how much current the 3/0s would deliver. 250.122 tells us on the LOAD side of a 200 amp OCP device the #6 will clear that current. It does not tell us a #6 would carry the necessary current delivered by a 3/0 on the LINE side of the 200 amp but on the load side of the 600.

 

[texie]

Note that I did say the bond jumper would not have to be larger than the phase conductor. I can find wording in 250.122 to support that, I can not find wording to support sizing it by the device at the end of the tap (ie: a #6 for a tap feeding a 200 amp switch).
In the case of a 100 amp panel, if we tap with a set of #3s and there is a line to conduit fault, the most current that could flow would be what the #3s could carry so a #3 bond jumper would be sufficient. If however the 3/0s to the 200 amp faulted in the supply conduit, the current flow, since it is on the line side of the 200 amp fuse, would not be limited to that covered by table 250.122 for a 200 amp feeder. 250.122 tells us a #1 bond is sufficient for the 600 amp
Without serious engineering data, we don't know how much current the 3/0s would deliver. 250.122 tells us on the LOAD side of a 200 amp OCP device the #6 will clear that current. It does not tell us a #6 would carry the necessary current delivered by a 3/0 on the LINE side of the 200 amp but on the load side of the 600.

I agree and with your post #11. The wording you are looking for is 250.122(G).