Bonding of Neutral bus and Ground bus at Main Panel.

[JPEE]

Good day engineers, I've read that, bonding of neutral bus and ground bus shall only be done at the MAIN PANEL. As graphically illustrated in Sir Mike Holt books, the main panel which contains the Main disconnecting device is separated from the branch circuit protective devices (which is technically, Sub-Panel). My inquiry is this,
1. What if the construction of the panelboard is "T-LINE PANELBOARD" wherein in this type of arrangement, the main disconnecting device and all the branch circuit protective device contained in one casing. Is bonding of neutral bus and ground bus mandated?
2. If bonding of neutral bus and ground bus are/will be mandated in 'T-LINE PANELBOARD", I believe it will energized the normally non-current equipment, because all the metal parts, like gas/water pipes are bonded in the ground bus. pls help me solve this.

 

[Dsg319]

Good day engineers, I've read that, bonding of neutral bus and ground bus shall only be done at the MAIN PANEL. As graphically illustrated in Sir Mike Holt books, the main panel which contains the Main disconnecting device is separated from the branch circuit protective devices (which is technically, Sub-Panel). My inquiry is this,
1. What if the construction of the panelboard is "T-LINE PANELBOARD" wherein in this type of arrangement, the main disconnecting device and all the branch circuit protective device contained in one casing. Is bonding of neutral bus and ground bus mandated?
2. If bonding of neutral bus and ground bus are/will be mandated in 'T-LINE PANELBOARD", I believe it will energized the normally non-current equipment, because all the metal parts, like gas/water pipes are bonded in the ground bus. pls help me solve this.

I don’t know what a T-Line panel board is. But if your concern is the Neutral energizing normally non current carrying parts, that is not a thing unless you have open neutral.

You have to have the neutral to egc bond or else you will have no hope in clearing ground faults.

I’m unsure exactly what your concern is. Feel free to enlighten me as I’m very capable of just plain out not understanding.

 

[Dsg319]

I don’t know what a T-Line panel board is. But if your concern is the Neutral energizing normally non current carrying parts, that is not a thing unless you have open neutral.

You have to have the neutral to egc bond or else you will have no hope in clearing ground faults.

I’m unsure exactly what your concern is. Feel free to enlighten me as I’m very capable of just plain out not understanding.

Main breaker up top and branch breakers below on both sides?

 

[JPEE]

I don’t know what a T-Line panel board is. But if your concern is the Neutral energizing normally non current carrying parts, that is not a thing unless you have open neutral.

You have to have the neutral to egc bond or else you will have no hope in clearing ground faults.

I’m unsure exactly what your concern is. Feel free to enlighten me as I’m very capable of just plain out not understanding.

 

[JPEE]

I don’t know what a T-Line panel board is. But if your concern is the Neutral energizing normally non current carrying parts, that is not a thing unless you have open neutral.

You have to have the neutral to egc bond or else you will have no hope in clearing ground faults.

I’m unsure exactly what your concern is. Feel free to enlighten me as I’m very capable of just plain out not understanding.

good day sir, I sent the photo above of what is a "T-Line panelboard". Clearly, you can see that the main disconnect are in the same casing with all the branch circuit OCPD. If neutral bus and ground bus will be bonded on that arrangement, the EGC which bonded to all non-current carry equipment like gas pipe will be energize. I hope you can imagine what I am trying to say.

 

[Dsg319]

good day sir, I sent the photo above of what is a "T-Line panelboard". Clearly, you can see that the main disconnect are in the same casing with all the branch circuit OCPD. If neutral bus and ground bus will be bonded on that arrangement, the EGC which bonded to all non-current carry equipment like gas pipe will be energize. I hope you can imagine what I am trying to say.

If that is your service disconnect, you must have your bond there. How will doing so energize anything?

 

[Dsg319]

If your on 2020 NEC i doubt if that panel is Suitable for a Service disconnect As there’s no barrier between service disconnecting means.

 

[ActionDave]

good day sir, I sent the photo above of what is a "T-Line panelboard". Clearly, you can see that the main disconnect are in the same casing with all the branch circuit OCPD. If neutral bus and ground bus will be bonded on that arrangement, the EGC which bonded to all non-current carry equipment like gas pipe will be energize. I hope you can imagine what I am trying to say.

Not true. If you don't bond the neutral to the ground you have no way to clear a ground fault. The presence of a main breaker has no effect on this.

 

[kwired]

First this is a 230/400 VAC panel used in places where NEC usually doesn't apply.

But as others have said, you have to bond neutral and grounding conductors at some point. NEC permits (more like requires) at the service disconnect. Ignore codes a moment, if it were done before that point you would need to supply it with separate neutral and grounding conductors that are bonded together at some upstream point for the grounding/bonding features to work as intended.

 

[LarryFine]

If neutral bus and ground bus will be bonded on that arrangement, the EGC which bonded to all non-current carry equipment like gas pipe will be energize. I hope you can imagine what I am trying to say.

We can, but here's why you're wrong: The incoming service neutral (grounded conductor) "defines" the zero-volts-to-earth point for the premises, and bonding the metallic normally-non-current-carrying parts (panel enclosure, etc.) and electrodes (pipes, etc.) to the neutral makes sure there will be (almost) no voltage differences between them.

We know that an accidental contact between a non-grounded (hot) conductor and the neutral will trip a breaker or blow a fuse. The non-current-carrying parts must be solidly connected to the neutral at some point to assure that an accidental contact between a hot conductor and a grounded metallic surface will have the same result.

Now, an accidental break in the incoming service neutral can allow all of those bonded items (neutrals, grounding conductors, electrodes, etc.) to attempt to rise above zero volts to earth, but, by bonding of everything that is expected to be zero volts to earth together, we at least minimize any voltage differences, minimizing shocks.

Your theory does indeed point out why we only bond the normally-grounded parts to the neutral at the service, and maintain the equipment-grounding system separate from grounded conductors beyond that point. We can expect the grounding conductor to be at zero volts to earth, even if the grounded conductor rises from it.

Note that everything ahead of the service is bonded directly to the neutral; there is no EGC ahead of that point. The enclosures and other metallic parts are effectively considered part of the neutral conductor itself. The premises grounding system originates at the service neutral, where electrode conductors normally terminate.

In your panel, the neutral bus is insulated from the enclosure, while the grounding bus is attached to it. If this is the service, the cabinet (and EGCs) will be bonded to the neutral here. If this is not the service, the enclosure will not be bonded to the neutral here, but the enclosure must be solidly connected to the enclosure where the bond is made.

 

[kwired]

We can, but here's why you're wrong: The incoming service neutral (grounded conductor) "defines" the zero-volts-to-earth point for the premises, and bonding the metallic normally-non-current-carrying parts (panel enclosure, etc.) and electrodes (pipes, etc.) to the neutral makes sure there will be (almost) no voltage differences between them.

We know that an accidental contact between a non-grounded (hot) conductor and the neutral will trip a breaker or blow a fuse. The non-current-carrying parts must be solidly connected to the neutral at some point to assure that an accidental contact between a hot conductor and a grounded metallic surface will have the same result.

Now, an accidental break in the incoming service neutral can allow all of those bonded items (neutrals, grounding conductors, electrodes, etc.) to attempt to rise above zero volts to earth, but, by bonding of everything that is expected to be zero volts to earth together, we at least minimize any voltage differences, minimizing shocks.

Your theory does indeed point out why we only bond the normally-grounded parts to the neutral at the service, and maintain the equipment-grounding system separate from grounded conductors beyond that point. We can expect the grounding conductor to be at zero volts to earth, even if the grounded conductor rises from it.

Note that everything ahead of the service is bonded directly to the neutral; there is no EGC ahead of that point. The enclosures and other metallic parts are effectively considered part of the neutral conductor itself. The premises grounding system originates at the service neutral, where electrode conductors normally terminate.

In your panel, the neutral bus is insulated from the enclosure, while the grounding bus is attached to it. If this is the service, the cabinet (and EGCs) will be bonded to the neutral here. If this is not the service, the enclosure will not be bonded to the neutral here, but the enclosure must be solidly connected to the enclosure where the bond is made.

I think that is something that is misunderstood throughout the trade though. If you lose the service neutral and have a water pipe electrode that also is bonded to neighboring services it is low enough resistance path that you may never know the neutral was lost. Most other electrode types you will see rise in volts on bonded objects to local earth. Even simple voltage drop on the neutral will cause a small rise, and is a reason equipotential bonding is required in art 547 and 680 applications.

As far as equalizing voltage grounded conductor to earth, that is really only effective in the immediate vicinity of the electrode, and that potential can change within pretty short distance of the electrode.

The incoming service neutral however is fairly good reference to earth because of the large network on the grid with multiple electrodes everywhere on the grid, and your electrode at your service is just one more of those electrodes. That electrode benefits the entire network more so than it benefits your individual service. Like I said simple voltage drop on the service neutral will give it potential to true earth.