grounding panel boards

[jkpyke]

Here is a question about panel boards. 2 panelboards rated as suitable for use as service equipment make up a service for a building. One panelboard has a 200amp main circuit breaker and the other has a 100amp main circuit breaker. The ungrounded service conductors are size 350-kcmil copper. Ungrounded tap conductors to the 200 amp panelboard are size 3/0 awg copper to the 100A panelboard are size 3 awg copper. The grounded circuit conductor is run to each service enclosure. The grounding electrode conductor is run from the neutral in the wireway to the grounding electrode. Grounding electrode conductor taps are run from the grounding bus in the 100a panelboards to the grounding electrode conductor. The min. permitted size grounding electrode conductor tap for the 100A panelboard is?

If going by Table 250.122 it would be 8 awg? Since this is ungrounded this should be going under table 250.122 and not table 250.66? Would this be a big enough guage?

 

[raider1]

This question is asking about grounding electrode conductor sizing so you should be looking at 250.66.

By the way are these homework questions?

Chris

 

[Volta]

Here is a question about panel boards. 2 panelboards rated as suitable for use as service equipment make up a service for a building. One panelboard has a 200amp main circuit breaker and the other has a 100amp main circuit breaker. The ungrounded service conductors are size 350-kcmil copper. Ungrounded tap conductors to the 200 amp panelboard are size 3/0 awg copper to the 100A panelboard are size 3 awg copper. The grounded circuit conductor is run to each service enclosure. The grounding electrode conductor is run from the neutral in the wireway to the grounding electrode. Grounding electrode conductor taps are run from the grounding bus in the 100a panelboards to the grounding electrode conductor. The min. permitted size grounding electrode conductor tap for the 100A panelboard is?

If going by Table 250.122 it would be 8 awg? Since this is ungrounded this should be going under table 250.122 and not table 250.66? Would this be a big enough guage?

Are you sure this is what the original question asked?

 

[jkpyke]

Yes this is what the original question asked and to Chris this is an end of chapter question

 

[augie47]

Keep in mid what Volta told you in a previos thread:

As a rule of thumb, you can think of the two tables as 250.122 for circuits with overcurrent protection, and 250.66 for those without.

To use 250.122, you need to know the size of the OCP device on the line side. If there is none, you probably should be in the other table.

Grounding electrode conductors are associated with service (or SDS) condcutors ahead of any overcurrent so 250.66 will be your guide.

 

[erickench]

Just one question. Are both of these services tapped from a service lateral in the wireway? If they are then the size of the service lateral would be used to size the grounding electrode if it is taken from the neutral in the wireway.

 

[Volta]

Jkpyke: You probably want to look at 250.64(D).

 

[Smart $]

... The min. permitted size grounding electrode conductor tap for the 100A panelboard is?

...

The GEC taps to each panel are under the requirement of 250.64(D)(1), and sized per Table 250.66.

For a #3 Cu the minimum GEC tap size is #8 Cu or #6 Al.

 

[Volta]

But anytime you think of a GEC that is smaller than #6, think conduit- 250.64(B). Sometimes it's cheaper to use larger wire in practice.

 

[kwired]

If the grounding electrode is conductor is connected to the neutral in the wireway and you made taps from this point to the panelboards you have created a parallel path between the two points with the tap conductor and the neutral conductor.

You can make taps from each service enclosure to a common grounding electrode conductor or you can run the GEC to a common point as described in the OP or you can run separate GEC from each enclosure to grounding electrode system.

See 250.64(D) and following sections.

 

[Smart $]

If the grounding electrode is conductor is connected to the neutral in the wireway and you made taps from this point to the panelboards you have created a parallel path between the two points with the tap conductor and the neutral conductor.

It was not stated that neutral and ground are bonded together again in the panels. Bonding neutral to GEC in the wireway is permitted as long as there is no bonding elsewhere.

 

[kwired]

It was not stated that neutral and ground are bonded together again in the panels. Bonding neutral to GEC in the wireway is permitted as long as there is no bonding elsewhere.

The tap the op is trying to size is no longer a GEC because it is on the load side of the main bonding jumper. However the service conductors that it is run with have no overcurrent protection and therefore should be sized to 250.66 based on size of ungrounded conductors they are associated with.


quote from OP:

Grounding electrode conductor taps are run from the grounding bus in the 100a panelboards to the grounding electrode conductor.

If the neutral and ground are bonded together again at the panel(s) a parallel neutral is created. If the main bonding jumper is in the wireway the conductors in question are equipment grounding conductors and not grounding elecrode conductors.

 

[Smart $]

The tap the op is trying to size is no longer a GEC because it is on the load side of the main bonding jumper. However the service conductors that it is run with have no overcurrent protection and therefore should be sized to 250.66 based on size of ungrounded conductors they are associated with.

If the neutral and ground are bonded together again at the panel(s) a parallel neutral is created. If the main bonding jumper is in the wireway the conductors in question are equipment grounding conductors and not grounding elecrode conductors.

I'm okay with your interpretation... but please tell me where to find the requirement for sizing an EGC on the supply side of a service disconnecting means per Table 250.66.

 

[RUWired]

The OP has two seperate requirements to make this installation correct. The first one is the GEC. He chose 250.64(D)3 so no other taps or connections are required at the wireway or enclosures. The second requirement is bonding. 250.92(A) 1 and 2 require all wireways raceways and enclosures containing service conductors to be bonded together. A bonding jumper in the wireway to the raceways and to the wireway itself is needed and a bonding jumper in each panel is needed. This could be a wire or screw.

Rick

 

[Smart $]

The OP has two seperate requirements to make this installation correct. The first one is the GEC. He chose 250.64(D)3 so no other taps or connections are required at the wireway or enclosures. The second requirement is bonding. 250.92(A) 1 and 2 require all wireways raceways and enclosures containing service conductors to be bonded together. A bonding jumper in the wireway to the raceways and to the wireway itself is needed and a bonding jumper in each panel is needed. This could be a wire or screw.

Rick

Spot on.

Getting back to the OP, the question itself is misworded (perhaps intentionally), as it leads one to believe GEC taps to each panel are required. I wonder what answer the book provides...

 

[tommyrice]

grounding panelboards

grounding panelboards

if i understand the question correctly,you wouldnt need to run egc tap from wireway to each panel if nuetral was grounded to electrode in wireway.you would only run phase wires and nuetral to panels.panel enclosure would be bonded to nuetral because panel is still considered service equip.(pg 121 soares)

 

[kwired]

I'm okay with your interpretation... but please tell me where to find the requirement for sizing an EGC on the supply side of a service disconnecting means per Table 250.66.

After further review I withdraw calling the conductors in question equipment grounding conductors. I will not call them grounding elecrode conductors either.

250.92 requires service enclosures and raceways to be bonded together and gives us a few options on how we may do this. If the OP is doing it through the taps mentioned then I would say they need sized per 250.66. He is really sizing a bonding jumper and not a GEC or EGC. If he already has a bonding jumper (like the factory supplied screw in most cases)
then his taps are not needed and if installed create a parallel neutral.

Of course if he has a metal raceway between service enclosures the raceway is a parallel path for the neutral, but the NEC sees this as acceptable. It needs bonded but most of the time it will it will become a parallel neutral path also. I try to keep these paths as short as possible if I have them or try to use non metallic raceways if possible.

 

[Smart $]

...

Of course if he has a metal raceway between service enclosures the raceway is a parallel path for the neutral, but the NEC sees this as acceptable. It needs bonded but most of the time it will it will become a parallel neutral path also. I try to keep these paths as short as possible if I have them or try to use non metallic raceways if possible.

I agree. In this case the bonding screw should not be installed when using conductive conduit and fittings. An alternative would be to install with a PVC nipple between wireway and panel, then use the bonding screw or a bonding jumper. I prefer the bonding jumper be installed regardless of nipple type used.

 

[cripple]

grounding panel boards

Here is a question about panel boards.
1. 2 panelboards rated as suitable for use as service equipment make up a service for a building.
2. One panelboard has a 200amp main circuit breaker and the other has a 100amp main circuit breaker.
3. The ungrounded service conductors are size 350-kcmil copper.
4. Ungrounded tap conductors to the 200 amp panelboard are size 3/0 awg copper, to the 100A panelboard are size 3 awg copper.
5. The grounded circuit conductor is run to each service enclosure.
6. The grounding electrode conductor is run from the neutral in the wireway to the grounding electrode.
a. 250.64(D)(3) is only one way of meeting the requirements of 250.64, which requires the grounding electrode conductor to be terminated in the wireway.
b. Code requires the main bonding jumper to be located were the grounding electrode conductor is terminated.
7. Grounding electrode conductor taps are run from the grounding bus in the 100a panelboards to the grounding electrode conductor.
a. If you chose to use 250.64(D)(3) no grounding electrode or equipment grounding conductor is required from the wireway to ether panel,(service disconnecting means).
8. The min. permitted size grounding electrode conductor tap for the 100A panelboard is?
a. The grounded conductor is required form the wireway to each service disconnecting means.
b. Each service disconnect (the 200 and the 100) requires a main bounding jumper at each service disconnecting means enclosure.
c. The main bounding jumper is required to be sized per 250.66.
d. The 200 amp service main bounding jumper based on 3/0, would no less than 4 AWG copper or 2 AWG aluminum, the 100 amp service main bounding jumper based on 3 AWG would be not less than 6 AWG copper or 4 AWG aluminum.
9. If going by Table 250.122 it would be 8 awg?
a. Table 250.122 cannot be use since you have not overcurrent device.
10. Since this is ungrounded this should be going under table 250.122 and not table 250.66?
a. NO
11. Would this be a big enough gauge?
a. NO

 

[eprice]

The tap the op is trying to size is no longer a GEC because it is on the load side of the main bonding jumper. However the service conductors that it is run with have no overcurrent protection and therefore should be sized to 250.66 based on size of ungrounded conductors they are associated with.


quote from OP:



If the neutral and ground are bonded together again at the panel(s) a parallel neutral is created. If the main bonding jumper is in the wireway the conductors in question are equipment grounding conductors and not grounding elecrode conductors.

The main bonding jumper cannot be in the wireway, See 250.24(B). I think that section requires the main bonding jumper to be in the service enclosures. It is true that the GEC can be connected to the grounded conductor in the wireway, but that does not constitute the main bonding jumper. The main bonding jumper's purpose is to connect the grounded conductor to the equipment grounding conductors and the service enclosure.