Service equipment

[hhsting]

As main service disco I have 200A panelboard with 200 MCB. You are suppose to bond the non current carrying metallic service disconnect enclosure to which one of the following and where is it stated in code:

1. Neutral bar
2. Equipment grounding conductor bar


no its not a test question.

 

[Buck Parrish]

1 and 2 are the same until they leave the first disconnect.
They may look different in the disco. So you would want to connect closest to the utilities neutral. NEC. Art 250
Obviously at the 2nd panel they would be isolated and non current metal is bonded to the equipment ground.

 

[hhsting]

Where in code it says bond service disco enclosure with neutral is ok? Would 250.142(A)(1) do or some other code?

 

[infinity]

Look at 250.24(C).

250.24(C) Grounded Conductor Brought to Service Equipment.
Where an ac system operating at 1000 volts or less is grounded
at any point, the grounded conductor(s) shall be routed with
the ungrounded conductors to each service disconnecting
means and shall be connected to each disconnecting means
grounded conductor(s) terminal or bus. A main bonding
jumper shall connect the grounded conductor(s) to each serv‐
ice disconnecting means enclosure. The grounded conduc‐
tor(s) shall be installed in accordance with 250.24(C)(1)
through 250.24(C)(4).

 

[david]

look also at 250.80

 

[LarryFine]

As main service disco I have 200A panelboard with 200 MCB. You are suppose to bond the non current carrying metallic service disconnect enclosure to which one of the following and where is it stated in code:

1. Neutral bar
2. Equipment grounding conductor bar


no its not a test question.

As most panels are constructed/supplied, #2 would be redundant.

 

[hhsting]

Not sure as I am still confused.

Please see attached sketch shows Option A and Option B. Option A has bonding jumper to service disco from neutral bar. Option B has bonding jumper to service disco from equipment grounding conductor bar. Both options have GEC to grounding electrodes from neutral bar.

Which is code compliant Option A or Option B in attached sketch?

 

[suemarkp]

Note that in Service Equipment, the equipment grounding bar is not needed -- the neutral bar can serve both purposes. So I'd say A is more correct. Most Service Equipment comes with a green screw you insert to act as the main bonding jumper. Typically, this goes through the neutral bar or to a dog leg into the neutral bar. I've seen panels that have a bar connecting the grounding bar to the neutral and the green screw goes into it (hybrid of options A and B as main bonding jumper screw is in the connection between the two bars and the connection to the neutral bar can be removed if you don't want it as a service panel). Also note that accessory grounding bars typically screw into the panel and those screws should bond it to the panel chassis so you don't need an explicit jumper from a hard mounted ground bar to the chassis.

What I'm unsure of is whether Option B is not allowed. Electrically it works, and the only risk I see is if someone removes that ground bar you've lost the main bonding jumper. I would expect you need to follow the manufacturer's instructions as to where the main bonding jumper goes, and they'd probably want it in the neutral bar.

 

[hhsting]

What if post #7 attachment was meter stack with 6 service discos and all bonding jumpers are wires and has two bars one neutral and another equipment grounding bar then Option A or Option B in the attachment be code compliant?

 

[LarryFine]

Not sure as I am still confused.

Please see attached sketch shows Option A and Option B. Option A has bonding jumper to service disco from neutral bar. Option B has bonding jumper to service disco from equipment grounding conductor bar. Both options have GEC to grounding electrodes from neutral bar.

Which is code compliant Option A or Option B in attached sketch?

Now that I see the two drawings, I say either is compliant. The main bonding jumper is the conductor between the buses in both drawings. The enclosure jumper is to bond the cabinet to everything else.

The bond of the cabinet to the neutral can be through a conductor, a bus, or a combination. The EGC bus is usually mounted directly to the cabinet, which is why I called Option B a redundant connection.

In fact, I believe that one of the two jumpers in A could be eliminated. Also, I would say that, in either case, with the EGC bus attached to the cabinet, the jumper to the cabinet in both drawings is redundant.

 

[david]

What if post #7 attachment was meter stack with 6 service discos and all bonding jumpers are wires and has two bars one neutral and another equipment grounding bar then Option A or Option B in the attachment be code compliant?

If you attach to the "equipment ground Bus Bar", you would have to ensure that a main bonding jumper of a (wire or busbar) type bonding jumper bonds the two busbars together

 

[jaggedben]

The answer is the neutral, or both.

The service enclosure must be bonded to the neutral. See above. A lot of service equipment, but not all, comes with the neutral bonded to the enclosure by the factory. If it comes bonded by the factory it is typically allowed to be used only as service equipment.

If there is a separate equipment grounding bar, it must be bonded to the service enclosure or the neutral. Since those two options are already required to be bonded, you'll be bonding all three together regardless of how you go about it. You are not required to have an equipment grounding terminal bar in service equipment, although it's good practice. (It is not a code violation to bond all the equipment grounding to the service enclosure with separate terminations, provided they are proper terminations. It's just sloppy when you could use a bar.) Usually equipment grounding bars are attached to enclosures such that they are bonded by the attachment. You can also use an equipment grounding bar as the means to bond an isolated neutral and the enclosure together.

The only grounding item that you may not bond to the neutral through the service enclosure is a grounding electrode conductor.

 

[kwired]

Now that I see the two drawings, I say either is compliant. The main bonding jumper is the conductor between the buses in both drawings. The enclosure jumper is to bond the cabinet to everything else.

The bond of the cabinet to the neutral can be through a conductor, a bus, or a combination. The EGC bus is usually mounted directly to the cabinet, which is why I called Option B a redundant connection.

In fact, I believe that one of the two jumpers in A could be eliminated. Also, I would say that, in either case, with the EGC bus attached to the cabinet, the jumper to the cabinet in both drawings is redundant.

Agree with everything here and will add to the bold part - in option B the jumper between grounded conductor bus and EGC bar is your main bonding jumper and would need to be sized per 250.102, unless it were some factory supplied jumper and was listed as is.

 

[Buck Parrish]

Note that in Service Equipment, the equipment grounding bar is not needed -- the neutral bar can serve both purposes. So I'd say A is more correct. Most Service Equipment comes with a green screw you insert to act as the main bonding jumper. Typically, this goes through the neutral bar or to a dog leg into the neutral bar. I've seen panels that have a bar connecting the grounding bar to the neutral and the green screw goes into it (hybrid of options A and B as main bonding jumper screw is in the connection between the two bars and the connection to the neutral bar can be removed if you don't want it as a service panel). Also note that accessory grounding bars typically screw into the panel and those screws should bond it to the panel chassis so you don't need an explicit jumper from a hard mounted ground bar to the chassis.

What I'm unsure of is whether Option B is not allowed. Electrically it works, and the only risk I see is if someone removes that ground bar you've lost the main bonding jumper. I would expect you need to follow the manufacturer's instructions as to where the main bonding jumper goes, and they'd probably want it in the neutral bar.

I'm pretty sure you do need a jumper. It might depend on what's connected to the bar.

 

[suemarkp]

250.8 says a machine screw that engages with not less than 2 threads is a permissible way of bonding an enclosure. Mounting screws are usually 8-32 or 10-32, so 32 threads per in into 1/16 inch metal gives you two threads. Now if you're thinking the ground bar may need a connection to the neutral and can't rely on the metal chassis for that, I've never had a good answer for that. 250.28 says the main bonding jumper can be a green screw. It just never seemed all that good to me compared to a wire sized by 250.102.

 

[david]

250.8 says a machine screw that engages with not less than 2 threads is a permissible way of bonding an enclosure. Mounting screws are usually 8-32 or 10-32, so 32 threads per in into 1/16 inch metal gives you two threads. Now if you're thinking the ground bar may need a connection to the neutral and can't rely on the metal chassis for that, I've never had a good answer for that. 250.28 says the main bonding jumper can be a green screw. It just never seemed all that good to me compared to a wire sized by 250.102.

The code is clear about the type of main bonding jumpers that are acceptable as a bond between a grounding electrode conductor and the service ungrounded conductor

a screw type is not allowed for that purpose

 

[LarryFine]

Now if you're thinking the ground bar may need a connection to the neutral and can't rely on the metal chassis for that, I've never had a good answer for that. 250.28 says the main bonding jumper can be a green screw.

The premises EGCs may have the cabinet in the pathway; the cabinet-to-neutral bond itself, and GECs-to-neutral bond, may not.

Interesting that the cabinet bond must be via an approved method, yet the cabinet itself may be in the EGC-to-neutral pathway.

Unless I'm mistaken, of course.

 

[kwired]

The code is clear about the type of main bonding jumpers that are acceptable as a bond between a grounding electrode conductor and the service ungrounded conductor

a screw type is not allowed for that purpose

Most of us generally try to not have any connection at all between a grounding electrode conductor and a service ungrounded conductor - doing so typically results in high amount of current flow.

 

[kwired]

250.8 says a machine screw that engages with not less than 2 threads is a permissible way of bonding an enclosure. Mounting screws are usually 8-32 or 10-32, so 32 threads per in into 1/16 inch metal gives you two threads. Now if you're thinking the ground bar may need a connection to the neutral and can't rely on the metal chassis for that, I've never had a good answer for that. 250.28 says the main bonding jumper can be a green screw. It just never seemed all that good to me compared to a wire sized by 250.102.

you can't just use any screw that is green, you must use the one that the panel manufacturer tested and had included in listings and must also use it in the designated place they allowed for it.

Many 125 amp and less panels will use a 10-32 screw, they often also have machined area in the cabinet that has more thread contact area than what just the typical cabinet wall thickness would allow.

The GEC must also land on the grounded conductor bus and not on any EGC bus regardless of how they might be bonded in a service panel application. Structures supplied by a feeder however must have the GEC land on the EGC bus and not the grounded conductor bus, unless it is an application that does allow omitting the EGC and only running a grounded conductor with the feeder then the rules are same as for services.

 

[Buck Parrish]

What I was trying to say is. If you add a bar that you land neutrals on. A jumper is required. I think that was added to the NEC in 99