Can AC neutral and ground wire share the same bus?
Hairfarm
Solar Expert Posts: 225 ✭✭✭
So, in the world of AC is it considered ok to share the neutral bus with ground wires too?
Like these examples:
Attachment not found.Attachment not found.Attachment not found.
If I wired both ground and neutral wires together on the same bus (and then grounded that bus) it would seem to match what I see in many other installations online. Or is it "proper" to wire the grounds to their own dedicated ground bus. I'm referring to the AC load center / breaker box.
I see many different wiring systems. Some group the neutrals and ground together on the same bus and others use dedicated busses for the neutral and the ground. Do they do that for neatness and orginization? I'm not sure what the "right" way is.
Btw, I looked in my own load panel and neighbors recently and both were wired with both ground and neutral wires on the same bus with the bus grounded in one place. So I assume this ok for my off-grid cabin too then(?)
* I realize that a sub panel must NOT share the same bus for neutral and ground, but since my ac panel is my main panel then this should be acceptable right?
thanks,
Like these examples:
Attachment not found.Attachment not found.Attachment not found.
If I wired both ground and neutral wires together on the same bus (and then grounded that bus) it would seem to match what I see in many other installations online. Or is it "proper" to wire the grounds to their own dedicated ground bus. I'm referring to the AC load center / breaker box.
I see many different wiring systems. Some group the neutrals and ground together on the same bus and others use dedicated busses for the neutral and the ground. Do they do that for neatness and orginization? I'm not sure what the "right" way is.
Btw, I looked in my own load panel and neighbors recently and both were wired with both ground and neutral wires on the same bus with the bus grounded in one place. So I assume this ok for my off-grid cabin too then(?)
* I realize that a sub panel must NOT share the same bus for neutral and ground, but since my ac panel is my main panel then this should be acceptable right?
thanks,
Comments
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Re: Can AC neutral and ground wire share the same bus?
Neutral and ground must be bonded together at one and only one point. That point must be solidly grounded to earth.So, in the world of AC is it considered ok to share the neutral bus with ground wires too?
Like these examples:
Attachment not found.Attachment not found.Attachment not found.
If I wired both ground and neutral wires together on the same bus (and then grounded that bus) it would seem to match what I see in many other installations online. Or is it "proper" to wire the grounds to their own dedicated ground bus. I'm referring to the AC load center / breaker box.
I see many different wiring systems. Some group the neutrals and ground together on the same bus and others use dedicated busses for the neutral and the ground. Do they do that for neatness and orginization? I'm not sure what the "right" way is.
Btw, I looked in my own load panel and neighbors recently and both were wired with both ground and neutral wires on the same bus with the bus grounded in one place. So I assume this ok for my off-grid cabin too then(?)
* I realize that a sub panel must NOT share the same bus for neutral and ground, but since my ac panel is my main panel then this should be acceptable right?
thanks, -
Re: Can AC neutral and ground wire share the same bus?Neutral and ground must be bonded together at one and only one point. That point must be solidly grounded to earth.
And that applies to the AC side in my load panel too? -
Re: Can AC neutral and ground wire share the same bus?
It is a good idea to have them bonded in a single place. Mostly because if you need to un-bond them for some reason you do not need to re-wire everything. -
Re: Can AC neutral and ground wire share the same bus?And that applies to the AC side in my load panel too?
That's the only place where you have "neutral" and "ground": AC
In practical terms having them all on the same busbar could be considered "one N-G grounding point" but somehow I suspect inspectors might frown on it.
I've never seen anything like what your pictures show: always all the neutrals come together on one busbar and all the grounds on another with one connection between them. Usually this is because there is a neutral feed from 240 VAC split phase input. The busbars should be large enough to accommodate all circuits. If not, you're trying to cram too much into the box and it should be larger. -
Re: Can AC neutral and ground wire share the same bus?Cariboocoot wrote: »The busbars should be large enough to accommodate all circuits. If not, you're trying to cram too much into the box and it should be larger.
I bought a Siemens panel which claims to be good for 64 circuits and there were only two relatively small ground buses. I wrote them, and they sent me free ground buses to accomodate everything. May be you need extra ground buses too? -
Re: Can AC neutral and ground wire share the same bus?I bought a Siemens panel which claims to be good for 64 circuits and there were only two relatively small ground buses. I wrote them, and they sent me free ground buses to accomodate everything. May be you need extra ground buses too?
So you're saying they're all going cheapskate on us and not putting in big enough bars? Man, we used to always have slots left over! -
Re: Can AC neutral and ground wire share the same bus?I bought a Siemens panel which claims to be good for 64 circuits and there were only two relatively small ground buses. I wrote them, and they sent me free ground buses to accomodate everything. May be you need extra ground buses too?
Yeah, there is a ground bus kit option with the panel that I have in mind. Based on everyone's input, I''l be ordering it and using it for my ground bus to keep them separate from the neutral.
thanks, -
Re: Can AC neutral and ground wire share the same bus?
Actually I have one more question:
What is the best way to make the neutral to ground bond in the panel? Is it to simply run a ground wire from the neutral bus to the panel's metal case and affix with a screw? Or should I just run a wire from the neutral bus to the ground bus, then ground the ground bus straight to my earth rod with 8awg bare copper?
does that make sense? -
Re: Can AC neutral and ground wire share the same bus?Actually I have one more question:
What is the best way to make the neutral to ground bond in the panel? Is it to simply run a ground wire from the neutral bus to the panel's metal case and affix with a screw? Or should I just run a wire from the neutral bus to the ground bus, then ground the ground bus straight to my earth rod with 8awg bare copper?
does that make sense?
First you should look for any instructions that came with the panel on how to make a neutral-to-ground bond. Most panels that are intended to be service panels come with a jumper or screw that is installed to ground the neutral. Lacking such instructions or parts, the methods you've described would be fine.It is a good idea to have them bonded in a single place. Mostly because if you need to un-bond them for some reason you do not need to re-wire everything.
It is mostly because one does not want current ordinarily flowing through metal conduit and equipment grounding conductors. -
Re: Can AC neutral and ground wire share the same bus?
The Service Entrance (Main) panel will usually have the ground conductors and neutral on one bus (neutral bus), as shown in your photo. That is completely normal. The neutral bus is then grounded to a ground rod or water pipe, and there is a green bonding screw in the neutral bus that bonds the bus to the panel itself.
All sub panels and circuits beyond the Service Entrance Main must have a separate ground bus and neutrals, and grounds are kept separate.
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Chris -
Re: Can AC neutral and ground wire share the same bus?It is mostly because one does not want current ordinarily flowing through metal conduit and equipment grounding conductors.
Power normally flows in the neutral of a split-phase power system with unbalanced loads on L1 or L2. The ground only carries power in the event of a Ground Fault. Since the neutral in a split-phase 4-wire power system is a grounded conductor, it is normally used as ground on split-phase 240V appliances and motors instead of running 4 wires to the appliance or motor.
120V loads on L1 or L2 of the split-phase service will also have three wires - the "hot" consisting of either L1 or L2, the neutral (provides the return current to the transformer or generator), and the ground (carries power to ground in the event of a Ground Fault). Some 120V appliances or tools are "two prong" - only a hot and neutral going to them. Again, the neutral is a grounded conductor so this is completely legal under NEC or CEC, however a two-prong appliance or tool will not protect you from electrical shock in the event the hot conductor comes into contact with the case, since you provide the path to ground in that instance. Only with systems with a "floating" (ungrounded) neutral, common with small generators and mobile inverters, will you be protected from electrical shock if you come into contact with a hot conductor, due to the fact that there is no path to the power source thru ground.
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Chris -
Re: Can AC neutral and ground wire share the same bus?
Things with 2 prong plugs tend to be "double insulated"; i.e. plastic case that can't be energized should a wire break loose inside.
In the old days there was no safety ground and the cases were metal. That's when life was exciting! Then they added grounding wires that either screw in to or under the outlet plate screw - relying on that to be grounded (ha!). Finally they got 'round to the 3-prong plug, then ... plastic cases and 2-prong plugs again.
Gee, we could have saved a lot of bother if we just went to plastic cases to begin with!
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Re: Can AC neutral and ground wire share the same bus?ChrisOlson wrote: »All sub panels and circuits beyond the Service Entrance Main must have a separate ground bus and neutrals, and grounds are kept separate.
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Chris
I don't mean to hijack your thread Hairfarm, but I have a related question that Chris reminded me of. I have an AC panel for making all the connections from the inverter (s) and auto transformer. It's actually a Fexware 500 panel that I'm using for that. From there, I plan (am not quite off grid yet) to send 3 wire, split 120/240 vac to my main service entrance panel. I've been trying to figure out the best (code compliant) grounding option. My current service entrance has a ground wire running to the neutral bus bar. I was thinking of making the inverter panel the new grounding point for the neutral and disconnecting the service ground (which happens to be on a different earth grounding point in any case). So essentially my AC inverter panel and DC connection panel will be grounded to the same point (I've put in a separate earth equipment grounding rods), and my service entrance will not have a neutral to ground connection. I also believe that my AC inverter panel must be located within a certain distance of the main service panel? I will look that up again, but do recall reading about it in the past. Is this the proper way to ground or should I look at keeping the ground at the entrance service panel? My inverter panel is also located inside the house.
I'm also thinking of grounding the frames of the solar panels using a separate earth ground. (ie the one that the grid ground is currently using) -
Re: Can AC neutral and ground wire share the same bus?ChrisOlson wrote: »Power normally flows in the neutral of a split-phase power system with unbalanced loads on L1 or L2. The ground only carries power in the event of a Ground Fault. Since the neutral in a split-phase 4-wire power system is a grounded conductor, it is normally used as ground on split-phase 240V appliances and motors instead of running 4 wires to the appliance or motor.
Chris
There is another case where ground can carry power and that is in the event that the neutral line is broken. I have actually seen this happen with someone's house recently, and not totally out of the ordinary. We measured over 5 amps going though a water pipe (which was grounded) and likely making the circuit through the neighbors house, where it competed the circuit back to the neutral there. -
Re: Can AC neutral and ground wire share the same bus?
ChrisOlsonSome 120V appliances or tools are "two prong" - only a hot and neutral going to them. Again, the neutral is a grounded conductor so this is completely legal under NEC or CEC, however a two-prong appliance or tool will not protect you from electrical shock in the event the hot conductor comes into contact with the case, since you provide the path to ground in that instance. Only with systems with a "floating" (ungrounded) neutral, common with small generators and mobile inverters, will you be protected from electrical shock if you come into contact with a hot conductor, due to the fact that there is no path to the power source thru ground.
That statement just opened up a major door of perception for me. I love it when that happens.
The Service Entrance (Main) panel will usually have the ground conductors and neutral on one bus (neutral bus), as shown in your photo. That is completely normal. The neutral bus is then grounded to a ground rod or water pipe, and there is a green bonding screw in the neutral bus that bonds the bus to the panel itself.
My inverter-side AC load panel IS my main service entrance for my off-grid system. I plan to use a separate ground bus (optional kit for my panel) for my ground runs and ground my neutral with a chassis screw.
thanks! -
Re: Can AC neutral and ground wire share the same bus?ChrisOlson
That statement just opened up a major door of perception for me. I love it when that happens.
Here is what may be another door opener:
A three wire grounded appliance connects the metal case to the ground wire so that an internal short to the case will draw enough current to trip a breaker rather than send a smaller but fatal amount of current through you.
A GFCI takes it one better by looking to see whether the current going out the hot lead is exactly the same as what is coming back through the neutral. If you become part of the circuit to ground somehow, the GFCI will sense the extra current in the hot wire (as little as a few milliamps) and open the circuit.
What a lot of people do not realize is that a GFCI wired onto a two wire circuit will still give you the same protection, and its own internal test button will work properly.
An external tester, such as a home inspector would use, cannot test it, since it relies on sending some current through the non-existent ground.
The NEC allow such use of a three-wire GFCI outlet, as long as you attach a label indicating that there is no ground present.
The other really nice demo is that you can drop a hair drier into a plastic bucket of water and a GFCI will not trip, since none of the arcing and sparking is going to ground!SMA SB 3000, old BP panels. -
Re: Can AC neutral and ground wire share the same bus?Cariboocoot wrote: »In the old days there was no safety ground and the cases were metal. That's when life was exciting!
When I was in college the first time back when dinosaurs walked the earth, it was before double insulated power tools and three prong plugs. There was a frat tradition called "South Seas Island Weekend" where the frat houses would all be decorated like what frat guys (I was one) thought Tahiti looked like, with a lot of bamboo and temporary pools made from 2X4's, plywood, and Visqueen. Anyway, a couple of houses down from us a guy was standing knee deep in one of these pools and noticed that someone had left a circular saw lying next to it. He leaned over and picked it up, with immediate, predictable, and tragic results. He never had a chance. -
Re: Can AC neutral and ground wire share the same bus?The other really nice demo is that you can drop a hair drier into a plastic bucket of water and a GFCI will not trip, since none of the arcing and sparking is going to ground!
And that would be lethal, right, if the GFCI didn't trip? -
Re: Can AC neutral and ground wire share the same bus?northerner wrote: »I was thinking of making the inverter panel the new grounding point for the neutral and disconnecting the service ground (which happens to be on a different earth grounding point in any case). So essentially my AC inverter panel and DC connection panel will be grounded to the same point (I've put in a separate earth equipment grounding rods), and my service entrance will not have a neutral to ground connection
To meet code, and make an inspector happy, the system neutral/ground bond should be made at the Service Entrance. The Service Entrance is defined as the place where the Main is that shuts off all the power.
In reality, that bond can be made anywhere as long as it's only made once. But where an inspector will have a problem with leaving the neutral/ground bond in your utility panel is if you have a switched neutral someplace (like in a generator transfer switch). So it's best to put it at the Main panel that shuts all the power off.
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Chris -
Re: Can AC neutral and ground wire share the same bus?What a lot of people do not realize is that a GFCI wired onto a two wire circuit will still give you the same protection ...
If the energy source is not grounded, there's no alternative route for the current. All current will always go through GFCI, so it'll never trip. In fact, if there's no ground, it's nothing that GFCI can protect you from. -
Re: Can AC neutral and ground wire share the same bus?
All a Ground Fault Interrupter does is measure the current difference between the hot conductor and neutral conductor. And it shuts the power if there's a difference. Contrary to what many people think a GFCI will NOT prevent you from getting an electrical shock. It simply shuts the power off before the shock can be fatal (in most cases).
You'll find some of the "double insulated" two-prong tools that have a small amount of leakage in the case or something, and they'll cause nuisance tripping of a GFCI.
NEC changes the book on GFCI every time the wind switches directions.
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Chris -
Re: Can AC neutral and ground wire share the same bus?ChrisOlson wrote: »And it shuts the power if there's a difference. Contrary to what many people think a GFCI will NOT prevent you from getting an electrical shock. It simply shuts the power off before the shock can be fatal (in most cases).
Few mA is enough to trip it. That's why they're expensive and prone to false trips. But if, as Bill says, 5mA through your heart is enough to kill you, GFCI may not trip and will not protect you at all. -
Re: Can AC neutral and ground wire share the same bus?ChrisOlson wrote: »To meet code, and make an inspector happy, the system neutral/ground bond should be made at the Service Entrance. The Service Entrance is defined as the place where the Main is that shuts off all the power.
In reality, that bond can be made anywhere as long as it's only made once. But where an inspector will have a problem with leaving the neutral/ground bond in your utility panel is if you have a switched neutral someplace (like in a generator transfer switch). So it's best to put it at the Main panel that shuts all the power off.
--
Chris
Thanks for that Chris, it makes sense to me now. I was thinking that the main service panel I currently have (ie where the grid power currently comes in) will become a sub panel, as my Flexware 500 panel will have breakers to shut off power as well, but the transfer switch can be used to bypass the inverter power. Technically, all the power could be shut off in the Flexware panel, but there isn't a single main breaker (unless another was added) to shut off all the power (both inverter and generator). Good point!
I think I will use a different earth grounding point for the main service ground, as I don't want my equipment ground to be tied into a ground common with one used by the grid. It seems that the grid picks up plenty of stray static, which will be fed to that common ground. I will use my own separate ground (which I currently have in place) to help protect the equipment. -
Re: Can AC neutral and ground wire share the same bus?northerner wrote: »I will use my own separate ground (which I currently have in place) to help protect the equipment.
We all have one common ground I don't think it has lots of interference from the grid. If you want to worry about ground, think of farmer's electric fences that work through the ground and can reach 50 miles! -
Re: Can AC neutral and ground wire share the same bus?We all have one common ground I don't think it has lots of interference from the grid. If you want to worry about ground, think of farmer's electric fences that work through the ground and can reach 50 miles!
I'm more concerned with large surges that are commonly picked up by the electrical grid and fed to ground. I don't want my ground to be in the close vicinity of the grid ground, as large dissipation events can be damaging. Even 50 feet of separation distance can make a big difference when dealing with the dissipation of large surges. -
Re: Can AC neutral and ground wire share the same bus?think of farmer's electric fences that work through the ground and can reach 50 miles!
Yeah, even if your buddies promise to pay you money to do it, it's a Really Bad Idea to pee on the electric fence
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Chris -
Re: Can AC neutral and ground wire share the same bus?northerner wrote: »I don't mean to hijack your thread Hairfarm, but I have a related question that Chris reminded me of. I have an AC panel for making all the connections from the inverter (s) and auto transformer. It's actually a Fexware 500 panel that I'm using for that. From there, I plan (am not quite off grid yet) to send 3 wire, split 120/240 vac to my main service entrance panel. I've been trying to figure out the best (code compliant) grounding option. My current service entrance has a ground wire running to the neutral bus bar. I was thinking of making the inverter panel the new grounding point for the neutral and disconnecting the service ground....
I'm no expert electrician, but have run in enough on solar forums to not only suggest, but recomend doing it this way. I've been told that you want the bond between the neutral and ground to be as close to the incoming power source as possible. This just makes the old panel a sub panel. E-Panels are typically setup as the main and send electric to you breaker box. As Chris said you want to have a disconnect at the main for AC and likely for DC and even solar input, so clear marking is required!Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites, Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects. -
Re: Can AC neutral and ground wire share the same bus?As Chris said you want to have a disconnect at the main for AC and likely for DC and even solar input, so clear marking is required!
Ah yes, I forgot marking. The Main should be marked as "MAIN". As an example, we did not buy the Power Distribution Panel for our XW Power System. Instead we got SquareD QO Load Center boxes - one as a combination AC Bypass for the generator/Service Disconnect, a second as a distribution panel that splits power out to the sub panels in my shop, and the house.
Although it may be hard to see here in this photo, the Service Disconnect panel is to the left of the inverter. It has a SquareD QO2DTI interlock for the AC Bypass. When the inspector came to sign off on this installation he made me put that blue sticker on the panel that says "MAIN" and made me put blue stickers on BOTH of those two-pole breakers that say "Service Disconnect" on them.
Attachment not found.
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Chris -
Re: Can AC neutral and ground wire share the same bus?I'm no expert electrician, but have run in enough on solar forums to not only suggest, but recomend doing it this way. I've been told that you want the bond between the neutral and ground to be as close to the incoming power source as possible. This just makes the old panel a sub panel. E-Panels are typically setup as the main and send electric to you breaker box. As Chris said you want to have a disconnect at the main for AC and likely for DC and even solar input, so clear marking is required!
That was my original plan. In any case, my system will have 2 disconnects for ac power, one at the inverter ac panel, and the other, already in place at the main service panel (to become a sub panel). If I add another main breaker at the inverter panel, it will become my service main shutoff. -
Re: Can AC neutral and ground wire share the same bus?ChrisOlson wrote: »Ah yes, I forgot marking. The Main should be marked as "MAIN". As an example, we did not buy the Power Distribution Panel for our XW Power System. Instead we got SquareD QO Load Center boxes - one as a combination AC Bypass for the generator/Service Disconnect, a second as a distribution panel that splits power out to the sub panels in my shop, and the house.
Although it may be hard to see here in this photo, the Service Disconnect panel is to the left of the inverter. It has a SquareD QO2DTI interlock for the AC Bypass. When the inspector came to sign off on this installation he made me put that blue sticker on the panel that says "MAIN" and made me put blue stickers on BOTH of those two-pole breakers that say "Service Disconnect" on them.
--
Chris
Good idea to label the service panel and of course a code requirement. Thanks for that Chris!
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