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ArkansasCabin
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# Posted: 3 Feb 2013 10:28pm
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I know you're not supposed to bond the neutral and ground more than once in any electrical system. Assuming my generator has the neutral and ground bonded, how do I go about wiring the neutral and ground into the load center which only has one ground bar/neutral bar?
Attached is the panelboard i wish to use. Its a 40A 2 space indoor load center.
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Rob_O
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# Posted: 3 Feb 2013 10:44pm
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That panel appears to have an isolated neutral bar. You would need to add a ground strip
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ArkansasCabin
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# Posted: 3 Feb 2013 11:13pm
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It's that simple? I should have figured. I'm guessing i would purchase a ground bar and just mount it to the housing of the panelbox?
thanks for your help
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Rob_O
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# Posted: 3 Feb 2013 11:26pm
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Quoting: ArkansasCabin It's that simple? I should have figured. I'm guessing i would purchase a ground bar and just mount it to the housing of the panelbox?
Yes, exactly
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rayyy
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# Posted: 4 Feb 2013 04:23pm - Edited by: rayyy
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When it comes to buying electric from the grid,it comes to your outlets in your home over the black wire(also known as the common or hot wire) from the power company's generator.But it has to return to their generator through the white wire to complete the circuite.(also called the nutral wire)The ground wire is there to return that electricity to their generator in the event your white wire should fail.It's just using the earth to return that current instead of a wire.That's why if your black wire should ever touch the metal of the box your outlets are in which is connected to the bare copper wire of your ground,or the white wire it would spark out and hopefully trip the breaker or blow the fuse.It's that breaker tripping or fuse blowing that keeps you from getting electricuted and or you place from burning down. Now when your generating your own electric from your own generator,it won't do you any good putting you earth ground to a copper grounding rod.As long as your ground is good and sound back to your generator from your outlets .That's why,as long as you bond your ground wire(bare copper) and your nutral(white wire)To that nutral bar,It's doing the same thing as if you were to go out and get you a seperate grounding bar.If you take a continuiety meter reading between the nutral bar and the metal box it sets in,you will get continuity.Meaning there are already connected together in that panel box.
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MtnDon
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# Posted: 4 Feb 2013 06:01pm
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Quoting: rayyy .If you take a continuity meter reading between the neutral bar and the metal box it sets in,you will get continuity.
I believe that depends on the box or service panel dresign. Mine have a special green screw that needs to be installed through the neutral bar to complete the circuit to the metal box/service panel itself. Without that screw in place there is no connection between neutral and anywhere else. The ground bar was an extra cost accessory and is mounted to the metal case
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PA_Bound
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# Posted: 4 Feb 2013 06:30pm
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My panel box had bar that ran between the neutral and ground buses, with a green screw into the box itself. That tied neutral, ground and box all together. At the end of the bar held on by the screw to the box, was small molded metal jumper that could be removed to seperate the neutral and ground buses. For use with a generator I just lifted that jumper. The box is still attached to the ground bus for proper grounding, but neither is attached to the neutral.
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Bzzzzzt
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# Posted: 4 Feb 2013 06:38pm
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Arkansas Cabin: Usually those kind of panels come with a green screw that screws into the neutral bar through a pre-existing hole in the bar into a threaded hole in the box itself which bonds the neutral and ground together. You have to install the screw if it is necessary.
That having been said, the NEC says that this bond should only occur ONCE in a system and it should be at the first disconnecting means. From there on there should be two separate wires and they should be kept separated in order to work properly.
Also, I would suggest driving a ground rod and attaching it to the generator housing. There is usually a lug on the generator somewhere just for this purpose. At the very least, drive the ground rod and run a #6 or #8 bare wire to the box you have pictured.
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neb
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# Posted: 4 Feb 2013 07:20pm
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Quoting: Bzzzzzt Arkansas Cabin: Usually those kind of panels come with a green screw that screws into the neutral bar through a pre-existing hole in the bar into a threaded hole in the box itself which bonds the neutral and ground together. You have to install the screw if it is necessary. That having been said, the NEC says that this bond should only occur ONCE in a system and it should be at the first disconnecting means. From there on there should be two separate wires and they should be kept separated in order to work properly. Also, I would suggest driving a ground rod and attaching it to the generator housing. There is usually a lug on the generator somewhere just for this purpose. At the very least, drive the ground rod and run a #6 or #8 bare wire to the box you have pictured.
Exactly
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toyota_mdt_tech
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# Posted: 4 Feb 2013 11:25pm
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You can purchase a separate ground bar. They sell them at home depot. Make sure you know the make/model of your panel, they can vary, but you can certainly make any of them fit. If its made for it,t he panel already has the holes in place. Then you need to remove the "bonding" screw. Will usually have a green screw or a tag letting you know. Isolate the neutral and add the ground bar.
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ArkansasCabin
Member
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# Posted: 5 Feb 2013 02:00am
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So what it sounds like..
I should install a seperate ground bar, isolate it from the neutral bar, and run my wires accordingly. I also should install a ground rod that connects directly to the housing of the breaker box through a heavier AWG wire.
Is it necessary to directly connect the generator to the ground rod, or will the connection to the breaker box suffice?
Thanks for everyones help.
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bldginsp
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# Posted: 5 Feb 2013 03:02pm
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It's a good idea to connect any generator that will sit in one spot to a ground rod. If it's portable and going to move, that's a problem.
Connection to earth does two things- protects against lightning doing damage (hopefully, not guaranteed) and equallizes any difference in potential between the earth and any metal equipment.
Sorry Rayyy, but the connection to earth has nothing to do with tripping a circuit breaker in the event of wvercurrent, be it a short, ground fault, or overload.
Ground fault, or fault current, exists when insulation on a hot wire rubs through and hot current gets onto metal parts of equipment. If the equipment is grounded (green or bare wire) then that wire completes a circuit back to the source (generator, utility transformer, inverter, battery) so that the amperage in the circuit can spike enough to trip the breaker. If the fault current has to go through the earth to get back to the source, the amperage will not spike enough to trip the breaker because the earth has too much resistance.
The reason you bond ground and neutral only at the main disconnect, or at the power source, is to avoid a parallel path for return current which can cause electrocution or arcing fire. If the grounds and neutrals are bonded in a subpanel, neutral current can get into the ground wires, where it then looks for a path back to the source. If it finds it it takes it, and if you touch that ground or equipment you can get shocked, or if that return current via the ground creates an arc somewhere it can start a fire.
Read Soares book on Grounding and Bonding for the complete story. Never rely on earth as a part of a ground fault clearing circuit.
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bldginsp
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# Posted: 5 Feb 2013 03:14pm
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You MUST bond the grounds and neutrals at least once in the system so that fault current can get back to the power source via a low impedance path, namely the neutral. The ground wire is like a bypass to get to the neutral to cause fault current to spike the amperage so the breaker throws.
The confusion arises because the 'ground' wire is what is being used to do this, and that ground wire is connected to earth (in the US, anyway), so people think the connection to earth is part of the circuit that clears the ground fault. But it isn't. It's the connection to the neutral that clears the fault. The connection to earth is only for lightning and equalizing any misc. imposed potential regardless of source.
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PA_Bound
Member
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# Posted: 5 Feb 2013 03:59pm
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Slightly off topic, but related to ground rods, can a steel well casing be used as a ground rod? I'm just thinking out-loud...
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bldginsp
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# Posted: 5 Feb 2013 06:02pm
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The authors of the NEC want you to bond your grounding electrode system to everything that can function as an electrode. A ground rod is generally the worst electode because it is small, but usually works well enough. A metal well casing, going deep into the earth, would be an excellent way to get a low impedance connection to earth.
That said, I have no idea whether experienced well installers would have any reason not to do so. There is no current in the electrode most of the time, but even slight currents can promote dielectric corrosion.
Any experienced well users got a perspective on this?
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ArkansasCabin
Member
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# Posted: 5 Feb 2013 09:19pm
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Wow tons of really valuable information here. Thanks again! and if i have any other questions regarding this topic, ill post it to this thread.
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toyota_mdt_tech
Member
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# Posted: 6 Feb 2013 10:41am
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bldg insp made a good point. If this is a primary panel, they can be bonded, if its wired as a sub panel, the ground and neutral should be isolated. I have my panel in mind and being as its not a secondary or sub panel, I kept the bonding together. If I ever tie it to the grid, it will be used as a sub panel, then I will decouple the ground and neutral. I assume I have that right.
I guess you can add the seperate grounding bar, run all the ground wires to it, neutral to the neutral bar witgh all neutral wires to it (white wires) , but leave the bonding screw in place. And if you use it as a sub panel, just pull the bonding screw out, done! Wiring is already correct.
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Bldginsp
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# Posted: 6 Feb 2013 12:22pm
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Hi Toyota - yes, if your current panel later becomes a sub, then isolate the grounds and neutrals in the sub and bond them in the new service meter enclosure.
And yes, many but not all panels are set up so that a bonding screw can connect the neutral bar to the panel box itself, which should be directly bonded to all grounds, thus the ground screw eliminates the isolation of the neutral. Manufacturers do this to give the installer the option, but the installer has to know what they are doing. It's actually quite rare that a sub panel bonds the grounds and neutrals, but it's possible to use the panel as service equipment where it's required, some transformer instals are allowed to bond at the panel, and in existing second building electrical installations where no ground is run with the feeders you are still allowed to bond at a sub if certain conditions are met. So anyway the manufacturers leave the option but can't tell you what to do since they don't know your particulars. But it provides for a lot of confusion, because sometimes people think that since it's made to bond the grounds and neutrals that therefore they should. Need to understand the concepts to configure an installation correctly.
When a panel is fed by a generator, should the bond be at the panel or in the generator? Not sure really. Most generators will bond the ground and neutral in the equipment, so if you isolated at the panel, the bond at the gen set itself should cause breakers to trip at fault current. But this depends on the connection of the ground prong on the extension cord plugged into the gen set, not necessarily the most reliable. If the gen set powered only the panel, I'd probably bond at the panel just to be sure the grounds are bonded to neutral. This then runs the dangers involved with allowing return current to take the ground wire of the extension cord back to the gen set. It also runs the possibility of return current finding it's way back to the generator via one of the ground wires in a house circuit, contacting metal that has a path to the gen set. What's the worst danger? Uncleared fault current due to a break in the extension cord ground path, or misc. return current presenting possibility of shock or arcing? I don't know, it's a judgment call, but I definitely want the circuit breaker to trip if the electric drill I'm holding screws up.
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bldginsp
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# Posted: 6 Feb 2013 01:29pm
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But, when a panel is fed by a stationary generator that is hard wired to a panel, I think the bond should occur at the generator. In this case the hard wiring should ensure the equipment ground path in case of ground fault, and any issues of return current in grounds is eliminated.
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sparky
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# Posted: 9 Feb 2013 06:54pm
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Where would a portable generator then be bonded?
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toyota_mdt_tech
Member
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# Posted: 9 Feb 2013 07:34pm
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In my cabin, my panel, the neutral and ground are bonded together. I do not have any at the generator except the ground wire at the plug. But the chassis isnt bonded to a ground. But my generator is all plastic. I cant touch any metal unless I open a service panel. Its fully insulated.
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bldginsp
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# Posted: 10 Feb 2013 11:17am
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I think, but I'm not sure, that all portable generator manufacturers bond the ground and neutral in the generator itself. This is necessary to trip the breakers in the generator in the event of ground fault. So long as you just use cords from the generator to equipment, with no panel in between, I guess you are relying on the bond at the generator. When you power a panel off a generator, then you have to ask the question, where to bond.
Does anyone have a generator manual that addresses this issue?
I'll see if I can dig up something in the Elec Code about this, but I don't think the issue is directly addressed, that is, I don't think there are specific rules regarding portable versus stationary generators. I could be wrong.
Good question, important to small cabin users.
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MtnDon
Member
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# Posted: 10 Feb 2013 12:22pm
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Generally speaking, if the generator has factory supplied, on board receptacles, then there is almost a certainty that there is a neutral/ground bond inside the generator. That should cover pretty much anything anyone is likely to own. On the other hand I know of one particular generac model that is meant to be hardwired to a system and there is no bond internal. That one is bonded at the service panel transfer switch.
While "generally" will likely be correct with what you own, the wiring diagram is the only certainty.
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sparky
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# Posted: 10 Feb 2013 01:08pm
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Wondering since a "hybrid" system is contemplated - portable generator semi hard wired in as so:
http://www.generlink.com/about_generlink.cfm
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Rob_O
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# Posted: 10 Feb 2013 01:49pm
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Quoting: ArkansasCabin So what it sounds like.. I should install a seperate ground bar, isolate it from the neutral bar, and run my wires accordingly. I also should install a ground rod that connects directly to the housing of the breaker box through a heavier AWG wire.
For your situation this is exactly what I would do. Ground wire only needs to be as thick as the extension cord connecting the panel to the genny, although oversizing it won't hurt
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bldginsp
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# Posted: 10 Feb 2013 02:04pm
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The electrical code makes no distinctions between portable and stationary generators, so the rules apply across the board. I take back what I said before, that I would bond at the subpanel. The bond should occur at the generator. My manual for my Briggs and Stratton 5500 watt generator specifically says that grounds and neutrals are bonded in the generator, and that the neutral is bonded to the generator frame. As MtnDon says, he's seen at least one generator that does not do this, which is a bit scary to think that a homeowner not knowing what they are doing might use one of these and never complete a ground/neutral bond.
Sparky, the device you linked to regards using a generator in conjunction with a utility service, which is another subject. Briefly, there are two dangers there: backfeeding the grid thus killing a lineman repairing wires, and maintaining ground/neutral bond when switching between utility and alternate power sources. The device you linked to, the Generlink, apparently takes care of both of these problems. Briefly reviewing it I did not see whether it has a UL listing, required by most jurisdictions.
Connecting a generator or other alternate power source to a utility system is often done with a main transfer switch which may or may not switch the neutral wire. If it does switch the neutral wire, the bond must occur at the generator. If the switch does not, the existing bond at the service functions to bond ground/neutral.
Hire an electrician if you want to connect a generator to a utility service.
The electrical code also says to connect every and any alternate AC power source to earth. So technically every portable generator should be on a ground rod, but we all know that's not going to happen. But, if your portable generator stays in one place all the time it's good idea to connect it to an electrode. This provides an extra safety factor to guard against electrocution from some kinds of ground faults, as well as lightning, but has nothing to do with tripping breakers in the event of ground fault.
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bldginsp
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# Posted: 10 Feb 2013 02:29pm
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RobO- Connecting a subpanel directly to earth is only required when it's in a separate building from a power source. The electrical code wants to see an electrode connection at the point where the neutral and grounds are bonded at the power source. So, if your generator is in the same building as the panel, the best place and only required place to connect to a ground rod is at the generator.
If the generator is in a separate building feeding the cabin via feeders, even if an extension cord, there should be a ground rod at both buildings, one to the generator and one to the panel.
In any case be sure there is a ground wire run from the power source to the subpanel. Ground at the subpanel must have a path to neutral, but not at the subpanel itself, so the ground run with the feeders is the only path to neutral, which is the bond of ground/neutral at the power source. This is what is meant when they say lead the ground 'back to XO'.
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MtnDon
Member
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# Posted: 10 Feb 2013 02:42pm - Edited by: MtnDon
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This is OHSA's stand on generators...
http://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf
Grounding Requirements for Portable
and Vehicle-mounted Generators
Under the following conditions, OSHA
directs (29 CFR 1926.404(f)(3)(i)) that the
frame of a portable generator need not be
grounded (connected to earth) and that the
frame may serve as the ground (in place of
the earth):
• The generator supplies only equipment
mounted on the generator and/or cord and
plug-connected equipment through
receptacles mounted on the generator,
§ 1926.404(f)(3)(i)(A), and
• The noncurrent-carrying metal parts of
equipment (such as the fuel tank, the internal
combustion engine, and the generator's
housing) are bonded to the generator
frame, and the equipment grounding conductor
terminals (of the power receptacles
that are a part of [mounted on] the generator)
are bonded to the generator frame,
§ 1926.404(f)(3)(i)(B).
Thus, rather than connect to a grounding
electrode system, such as a driven ground
rod, the generator's frame replaces the
grounding electrode.
If these conditions do not exist, then a
grounding electrode, such as a ground rod,
is required.
If the portable generator is providing electric
power to a structure by connection via a
transfer switch to a structure (home, office,
shop, trailer, or similar) it must be connected
to a grounding electrode system, such as a
driven ground rod. The transfer switch must
be approved for the use and installed in
accordance with the manufacturer's installation
instructions by a qualified electrician.
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bldginsp
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# Posted: 10 Feb 2013 02:46pm
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Whenever plugging any extension cord into a generator, make sure it has a good ground prong on the plug. We've all seen plugs with the ground prong broken or intentionally cut off. If there is no connection of the ground wire to the generator, you've lost any protection from ground fault, so when that hand drill or blender you are touching fries itself, you get electrocuted rather than the breaker tripping.
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bldginsp
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# Posted: 10 Feb 2013 03:01pm
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The OSHA sheet MtnDon gave us basically tells us that you are supposed to use a portable generator without connection to earth only when it has cord and plug equipment attached to it. An extension cord hooked up to a subpanel is beyond that, of course, so if that's how you are using it there must be a ground rod at the generator, at least according to them. I'm not sure if the elec code has this allowance for cord and plug appliances with generators, but it certainly requires earth connection of all sources otherwise.
Also, it should be said that connecting a subpanel to a generator with a cord and plug to begin with is questionable. I don't know whether the elec code prohibits this, but it makes the extension cord into a feeder which has separate rules. If the generator is in a separate building then the issues of safely running the feeders into the cabin should be looked at closely.
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