Grounding a Generator

[salmonslayer]

So along the same lines of the electric fence grounding thread, I have a question. I have been using a generator for literally a couple of decades both for personal use and while in the military and in all those years they were never grounded with a grounding rod (at least that I remember).

When I purchased my new generator a few weeks ago I was reading that you are suppoosed to ground the generator with a grounding rod but nothing says how big of a grounding rod or whether you use copper wire like you would to grount a residential electrical service.

So at the risk of much scorn for my lack of knowledge and previous unsafe use....what does everyone use to ground your generator? Its a 5500 kw and I am in the process of wiring in a transfer switch and want to do this right. Would a 3 foot copper rod work? And we have very rocky soil that often has voids so how do I tell if there is an adequate grounding?

[elevenpoint]

8' solid grounding rod driven flush....any building or electrical supply will have this

[salmonslayer]

ground

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8' solid grounding rod driven flush....any building or electrical supply will have this

Wow, I wasnt expecting the same type of ground as would be used for a residence for a portable generator. It almost sounds like I will need some type of permanent setup for it.

[anniew]

I was told my portable (on wheels) generator didn't need a ground because of the rubber tires...is that incorrect?

[sisterpine]

Don't know right or wrong but my generator is grounded to the same ground as the shed it sits next too and it is a big heavy long thing hammered into the ground?

[Heritagefarm]

Originally Posted by anniew

I was told my portable (on wheels) generator didn't need a ground because of the rubber tires...is that incorrect?

That doesn't make sense... Rubber is an insulator.

[Bearfootfarm]

Originally Posted by anniew
I was told my portable (on wheels) generator didn't need a ground because of the rubber tires...is that incorrect?

That's why it DOES need a ground

Ideally it should be a long rod, but reality is anything is better than nothing.
Most tend to use their generators in the same location at home, so putting in a good ground rod shouldnt' be a problem.

If you move it around a lot, just go with a shorter temporary set up

[Little_Bit_Red]

Not sure about what is found commercially - but I know that if the ground is bedrock or very hard, one can use a shallow dug hole with grounding plates that don't need to be very far into the ground. The plates are wired together and there is more than one plate. I know I am not explaining this very well...I will look for a picture or a link. The other thing is that in dry areas, one needed to keep the burried plates wet with some type of appropriate liquid...

INFO post to follow

[Little_Bit_Red]

http://www.globalsecurity.org/milita...-424/chap8.htm

GROUNDING ROD
The standard grounding rod used by military units is a 5/8-inch copper rod with three 3-foot sections. To install a grounding rod, drive it at least 8 feet into the soil. The rod must be buried below the moisture level. If you cannot do this, replace the grounding rod with an 8-foot electrode. Bury the electrode in a horizontal trench that is at least 2 1/2 feet deep, and place the electrode below the moisture level.

If one grounding rod does not produce a good grounding system, you can form a network with three or more rods. Install the rods about 6 feet apart. If three rods form the network, place them in a straight line or in a triangular pattern. If more than three rods are used, install them in a straight line and connect the grounding cable from the generator set to each grounding rod so they are in series.

GROUNDING PIPE
Use a clean, metallic pipe of 3/4-inch trade size or larger to make a grounding pipe. Pipes made of iron or steel must be galvanized or coated for corrosion protection. Drive the pipe at least 8 feet into the soil. If you cannot do this, replace the pipe with an 8-foot-long electrode. Bury the electrode in a horizontal trench that is at least 2 feet deep and place it below the moisture level.

GROUNDING PLATE
You may use a buried grounding plate (plate electrode) as a ground. The plate must be at least 36 inches wide and 36 inches long (9 square feet). An iron or steel plate may be substituted for a plate electrode if it is at least 1/4-inch thick and coated for corrosion protection. Grounding plates must be buried below the moisture level.

Attach the grounding system with a No 6 AWG or larger cable. Connect one end of the cable to the grounding terminal of the generator set. Tighten the nut securely, as described in the appropriate TM. Connect the other end of the cable to the grounding electrode with a special grounding clamp.

SOIL CONDITIONS
Contact with the earth does not guarantee a good grounding system. The soil type, moisture content, and temperature affect the efficiency of the grounding system. Table 8-10 describes the characteristics of four types of soils.


Table 8-10. Soil characteristics
Type of Soil
Quality of Ground

Fine soil granules with high moisture content
Very good

Clay, loam, shale
Good

Mixed (clay, loam, shale mixed with gravel or sand)
Poor

Gravel, sand, stone
Very poor





Soil is divided into two distinct layers. Topsoil, the first layer, usually ranges from 1 to 6 inches deep. Because it is often dry and loosely packed, topsoil is not a good electrical conductor. Subsoil, the second layer, is usually tightly packed, retains moisture, and provides the best electrical ground. Wet soil passes electrical current better than dry soil and allows the grounding system to work efficiently.

A chemical solution is used on soils to improve a poor grounding system. To make this solution, mix 5 pounds of sodium chloride (common table salt) with 5 gallons of water (1 pound of salt to 1 gallon of water). Dig a hole that is about 1 foot deep and 3 feet wide. Pour the solution into the hole and allow it to seep into the soil. Install the grounding rod in the hole, connect the grounding strap, and fill the hole with soil. Keep the soil around the rod moist at all times.

Frozen soil is a poor conductor of electrical current. When the soil temperature drops below 32°F and the soil moisture freezes, the effectiveness of the grounding system decreases. To compensate for low soil temperatures, place the grounding system near a source of heat such as a generator set or vehicle exhaust. When it is difficult to install an effective grounding system because the soil is frozen, connect the grounding strap to something that is already grounded, such as a metal building or an underground pipe. If possible, attach the strap with a grounding clamp; if not, attach it with a bolt.

Another alternative is to drive several grounding stakes into the soil at different locations to form a grounding network. Drive the stakes to the greatest depth possible. If necessary, drill, dig, or blast a hole in the soil and use the salt solution described previously. You may also be able to make a temporary ground by driving a spike deep into a large tree.

Geographical locations are important considerations when establishing grounding systems.

■Deserts. The extremely dry and loosely packed desert soils provide a very poor electrical grounding system. Increase the efficiency of the grounding system with the salt solution. Keep the soil around the grounding system moist at all times. Place the equipment near an oasis or subterranean water if possible. ■Mountainous areas. In the rocky terrain typical of mountainous areas, site selection is the key to providing a good grounding system. Try to place the equipment near a streambed. ■Packed, rocky, or frozen soil. Use a slip hammer to drive a grounding rod into this soil. You can make a slip hammer (Figure 8-16), or you can order one through normal supply channels.



■Tropical areas. Soils in jungles and rain forests provide good electrical ground for the grounding-rod assembly issued with the generator set. You can install grounding rods easily in these moist soils. The fast buildup of corrosion is a problem in the tropics. To ensure a good electrical path, apply waterproof tape at the connection of the grounding strap and keep the grounding rod clean and dry.
Perform the following checks and services to establish a good grounding system:

■Remove paint, oil, and grease from the grounding rods, straps, and connections. ■Keep grounding rods and straps clean. ■Ensure that grounding rods are as straight as possible. ■Keep the points of grounding rods sharp enough to penetrate the soil. ■Ensure that the straps and cable are the proper lengths. ■Use the proper clamps and connections for the grounding system selected. ■Properly tighten the terminal screw and the grounding-clamp screws.

[Harry Chickpea]

Oy. So many misconceptions.

Rubber tires contain carbon black. Pure rubber is an insulator. Rubber tires are, more often than not, NOT.

There are various purposes for grounds. Any radio equipment tends to work a lot better when there is a proper ground, but the issue with portable generators is the possibility of shocks and electrocution.

IF a generator is on a wooden stand AND it doesn't rain AND there is no possible connection between the generator and the ground, then by definition, there is no possibility of a return path for current through the ground. In 99% of the cases, the ground resistance and lack of good contact between the generator case and the area where you are using a tool effectively makes a ground superfluous.

HOWEVER, in our nanny culture, backed up by insurance agents and lawyers with nasty sharp pointy teeth, that 1% of the time, and the 1 in 10,000 chance of an accident have forced changes in laws. Think of it not only as "belt and suspenders" but "belt suspenders and Depends." I can flat out guarantee, if someone figured out a way to use electricity with only ONE conductor and eliminate the possibility of shocks, attorneys would drive the industry to adopt that standard, no matter how expensive.

I'm not going to tell anyone to go against electric code. You might put your eye out.

[ronbre]

mine says to use an 8' grounding rod with the copper wire too..we didn't quite pound it in flush as we intend to move it so we left enough to be able to pull it back out with the tractor..when we need to move it.

[salmonslayer]

Lots of good information folks thanks. I also understand what your saying Harry, I kind of wonder how many people actually use grounding rods as I never see them on portable generators and I used one at camp and on our fishing boat for years without a ground. When I bought this one new and read the directions it just jumped out at me as I never even thought about it. (and the tires on the thing are never flat...i.e., cheap plastic). The directions also didnt cover one thing about what you actually need...probably due to liability concerns.

I think I will follow BFF and Brenda's lead and make a spot for it with an 8' ground for the house backup where I plug into the transfer switch and then have a smaller rod for when I'm using it somewhere else. Kind of makes me wonder what else I have been doing wrong all these years!!

[tiogacounty]

If you are using it for a properly installed transfer switch, you will be connecting it with a four wire cord, typically it's the black flexible stuff labeled "SO", and contain four #10 wires, thus the cord will be marked 10/4 SO, or similar. The cord will have a four prong, twist lock plug on each end. The system when operating, will provide two hot legs of 120 volts. These are the black and red wires and combined they will provide 240volts. There will also be a white wire, which is the neutral for use on 120 volt circuits, and a GROUND. This is where your generator is grounded. The ground is established at the house electrical service and is connected, via the cord, to the generator, just like everything from a toaster to a portable circular saw would be, when plugged into the house. If you want the belt and suspenders approach, take a solid, bare or green #10 wire, attach it to the external ground lug on the generator and run it to the bare wire attached to your house's ground rod. This can be done with a connector called a split bolt. (about $3 at Lowes or HD) Now your generator and home are both grounded with a common bond. You DO NOT want to ground the generator independently from the home, with a driven rod. This can create a hazard know as a difference of ground potential. It's complicated and unusual to have issues with it, but it's real and a potential hazard. As an electrician, I have been literally knocked on my butt by it. BTW, this ground differential is the issue with animals who will not drink from waterers or fear metal stalls. they are far more sensitive to it, and can detect far lower levels of stray voltage. Good luck. As for driving rods every time you use a generator, don't bother. Even with some of the safety obsessed giant contractors I have worked for, the only requirement is that you have a GFCI adapter plugged in between your extension cord and the generator when working. These are on the shelf at Lowe's and HD also. They cost a bit, around $30 IIRC, but they will provide a lot more safety than trying to drive grounds for temporary use.

[10ecn]

Because of shallow rock, I've been using a concrete form stake, and a piece of romex for several years. Not that I'd recommend it, but it's worked for me, so far. Also, my situation is different. My generator (5K) is used to run power tools, and charge batteries, in a structure that has no access to store bought electricity, and is not wired for it. I use only 110 volts, try to exercise common sense, and do not fool with it when it's damp or raining. If using one for back up to a public utility, I would definately consult with an electrician.

[Harry Chickpea]

tiogacounty has nailed it. Great advice.

[tiogacounty]

Originally Posted by 10ecn

Because of shallow rock, I've been using a concrete form stake, and a piece of romex for several years. Not that I'd recommend it, but it's worked for me, so far. Also, my situation is different. My generator (5K) is used to run power tools, and charge batteries, in a structure that has no access to store bought electricity, and is not wired for it. I use only 110 volts, try to exercise common sense, and do not fool with it when it's damp or raining. If using one for back up to a public utility, I would definately consult with an electrician.

It would be both difficult and expensive to test the value of your method of temporary grounding. The resistance to ground would vary greatly based on soil conditions and moisture content. that said, based on several decades of work in the trade, attending classes on the issue, and watching the latest upgrades to residential service grounding continually evolve, I would respectfully suggest that you are wasting your time on this. Testing has made it clear that a properly driven, 8' long copper clad 5/8" dia. ground rod is woefully inadequate in many cases and no longer acceptable for new service installations. A short steel rod is probably just providing another thing to trip over In you case, I would at least try to drive a full size rod in, or bury one as deep as possible in a trench, then connect it with an "Acorn" clamp and a bare piece of #10 solid. Good luck.

[salmonslayer]

Thanks Tiogacounty, you explained very well what had me confused and I like the GFCI solution for using when not connected to the transfer switch. I am installing a Reliance power transfer switch with a 30 amp plug in box outside (I am wiring it with 10/3 in conduit and the actual transfer switch is in my basement right next to the breaker panel)and a 30 amp locking power cord and I just got tripped up over the grounding requirements....now that you explained it I feel a lot better.

[tiogacounty]

Originally Posted by salmonslayer

Thanks Tiogacounty, you explained very well what had me confused and I like the GFCI solution for using when not connected to the transfer switch. I am installing a Reliance power transfer switch with a 30 amp plug in box outside (I am wiring it with 10/3 in conduit and the actual transfer switch is in my basement right next to the breaker panel)and a 30 amp locking power cord and I just got tripped up over the grounding requirements....now that you explained it I feel a lot better.

Glad I could help. Just to clarify one oddity in our discussion here. You state that you are using 10/3 in conduit. I assume that you are going to be running Romex in this conduit. This would mean that your 10/3 Romex has three insulated conductors black/red/white and a bare ground, for a total of four wires. Now, for the odd part. If you are making your own extension cord and shop for a matching 10/3 SO or SJ flexible cord, it will have three conductors, black, white, green. So you need to specify a 10/4 cord. Now, don't ask me why this is. I haven't go a clue, it just is, and it can get expensive if you remember after it is already cut off the reel and laying on the counter at the store. Good luck.

[Jim-mi]

Tioga has the good word..........
I have read of many who have big bad issues when putting a ground rod in at the generator.
Yes in this_PC__ day and age the mano's are gonna tell you to ground the machine.
How is the gen wired . . .???
Is the neutral tied to the frame . . .??? (take a meter and find out)

Like tioga said get a Good 10-4 SO cord and your done.

[Oldcountryboy]

What kind of generator are we talking about? A small portable on wheels or a permanent backup generator for your existing electrical service?

If it's a small portable generator, I wouldn't worry about it as your only going to be using for temporary service only. But a permanent backup generator does have to be grounded according to the NEC Code.