I am aware that "all generators must be grounded". In the instance of a standby portable generator like this
Which option here is more legal and more safe?
thanks
iGround it to the home system. I don't know the code details, but there is bare wire, known as "bonding wire", that code requires run without any splices from the box to the actual ground.
The important thing is that the ground be redundantly robust. If there is a ground fault, a hot-to-ground leak in a powered appliance would raise the potential of the chassis above ground.
Unlike neutral, which code says is to be bonded to ground at only one point, it is considered good engineering practice to "grid the ground", meaning multiple connections.
I would run an unspliced length of bonding wire from your box to the generator. Additional ground connections, such as a cold-water ground would provide redundancy.
What does a grounding rod cost???
That ground connection should be faultless and super safe and excessive, is a great point.
i am not so sure, myself, I remember reading otherwise.
Thanks.
i
I am not sure, I think that about $40, I may be mistaken. Plus, I have to pound it in, it could bend, right now everything is frozen, etc etc etc.
iI bought some ground rod this spring, and I seem to recall that they were about $8 for an 8' length. It's a simple steel rod, sharpened point and coated with copper.
I was surprised how inexpensive it was.
This is nice. Steel, I am sure, does not bend as easily either. Is there any issue with corrosion impeding conductivity?
i
There are a couple of issues here. Grounding the generator frame can be done via the Equipment Grounding Conductor in the cable you connect it with (to the building electrode). Certainly driving an additional rod when the ground thaws (~$10 plus about $5 worth of hardware) is a safer approach but it will still have to be bonded back to the house via the EGC. The other issue is grounding the neutral. If your transfer equipment switches the neutral you will need to ground the neutral in the generator. In most cases the transfer switch only transfers the hot legs so you leave the neutral isolated in the generator (as most portable generators are shipped). This grounds the neutral via your main bonding jumper in the service panel.
That makes sense. Thanks.
iDepending on how the generator will be used, it may not require a connection to a grounding electrode system. The NEC states that it you will have cord-and-plug connected equipment through the receptacles mounted on the gen, then it doesn't require grounding of the frame. Also if this is the case, then ensure that the manufacturer has bonded (connected) the neutral and ground within the generator, as it is a separately derived source. If the previous is not the case, then you must connect it to a grounding electrode system. If your are serving a premises with a grounding electrode system, it must be the same, meaning connect directly to it, or drive a rod and connect the rod to the existing grounding electrode system. It must be one grounding system, not isolated.
There are lots of other things to consider like how you will transfer the loads to the gen, and such, but go carefully.
Greg, NEC-2002 250.34(C) that requires the neutral to ground bond only if the generator is a separately derived source. It is only a separately derived source if the neutral of the sources are switched. See 250.20(D) FPN No1
source.
I believe that the neutral is bonded to the frame.
I also expect to have a transfer switch that will only switch hots.
i plan on having separate neutral and ground wires going from home to the genset.
That's exactly why I want to explore opinions and come up with a solid plan. I do not want to have the generator grounded separately without need.
i
I bought 5/8" copper-clad steel ground rods for $8.xx earlier in the year, but for the past couple of months or more they have been $13.xx at the same store. The price of steel products has been skyrocketing, allegedly because of the construction boom in China.
Perce
On 12/27/04 01:10 pm Bughunter tossed the following ingredients into the ever-growing pot of cybersoup:
Ron and I agree. I was just trying to avoid some of the NEC speak that confuses people. The point is you only want one bonding point between the neutral and ground and if the transfer equipment doesn't switch neutral that will be the jumper in your service panel. (Separately derived source is NEC speak for a system where the neutral is switched too so it will have separate bonding jumpers that go with the source). All the frame grounding will be bonded, no matter what the transfer scheme. Adding another electrode only insures that the ground on the case is more closely referenced to the dirt under your feet when you are standing there. Depending on where you live "ground shift" is more or less of a problem. Here is the sandbox (Florida) I have seen 35 volt transients across 30-40 feet between buildings.
You are connecting this to your home wiring with a transfer switch that switches only the hot connection. Is that correct?
I used to have a link to a long article that went into extreme detail and all that, but have misplaced it. Oh well. Anyhow...
If your generator ground is bonded to generator neutral, you MUST use a transfer switch that switches both hot and neutral, and you MUST ground the generator.
If your generator is not bonded (and no normally available generators are bonded afaik, but your monster...) then you can switch only the hot and MUST NOT ground the generator.
The article went on for pages about ground loops or somesuch thing (the neutral being grounded in two different places). So, my suggestion is that you find out if you can unbond your generator, since you are unlikely to find a transfer switch to switch both hot and neutral. There is no need to ground the generator separately, since it's ground is not connected to anything except the house ground.
That would be my plan, yes. I have not yet bought the transfer switch, but all ones available for "homeowners" seem to be such.
Which I think is the case, I will check tonight with an ohmmeter.
Aha. Thanks. It makes sense, logically.
Okay. I will check for sure tonight or soon, and will report my findings.
I will check and post updates. I am not sure just what possible dangers to the generator could be created by unbonding.
i
That's right you don't know the code details so shouldn't be offering advice.
I don't think that these rods are especially susceptible to corrosion.
I believe that the steel core is a standard feature. Yes, they look like solid copper but it's just a copper coating on the outside.
One of the rods in my home corroded and had to be replaced, but it took nearly 30 years. I can handle $8 - $15 maintenance expense every 30 years or so. Life may be shorter if you have more acidic soil.
You can drive into pretty hard ground with a good sized sledge hammer, but you are all done if you hit a hard rock. Lots of little firm taps works better than big swings, with less chance of bending the rod. Work slow until you get most of the rod into the ground, than you can take bigger swings.
NEC code has a spec for the amount of resistance that you must shoot for, I think it was something like 8 ohms. I did not see any description of how you actually measure it. If you can't get it on the first rod, you have to drive in a second. But, even if you don't do any better with the second, you can stop at two. I guess they figure if you don't get it after driving two rods, you chances of doing better with several is slim.
There are other possibilities, including buried mesh screens, and even attaching to rebar inside the concrete of the structure. Most of the other methods require a bit of pre-planning or more work to install.
If you buy steel cored copper rods, also pick up some heavy duty clamps brass or copper clamps that are made for this purpose to attach your ground wire to the rod. Usually, you use #6 braided copper with no insulator.
I believe like any sub-panel, the ground must run back to the main panel. Sorry that I can't remember what article this is in, maybe someone else can help with that.
later,
tom @
I heard a great tip for this. Use your hammer drill but on 'hammer only'. Let the machine do the work.
hth,
tom @
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