A little about grounding

[wiredwrong]

A while back there was a discusion about grounding a system and I found this and thought that I would share it with the rest of you. The following is a cut-n-paste from homepower magazine, issue #103

Grounding Electrode

The "grounding electrode" can be a number of different

devices. In many places, the commonly used electrode is an

8-foot (2.4 m) long, 5/8-inch (16 mm) diameter copper-coated

steel rod driven into the earth. The entire length of the rod

must be in contact with the earth, so the top is usually flush

with, or buried slightly below the surface. Clamps rated for

direct burial are used to connect the grounding-electrode

conductor to the grounding electrode.

The code requires that the resistance from the rod to

the earth be 25 ohms or less. This measurement is difficult

without specialized equipment. To do it accurately, you

have to use instruments that cost hundreds of dollars.

If the measurement is greater than 25 ohms, a second rod

must be driven at least 6 feet (1.8 m) away and bonded to

the first rod. The bonding conductor must be the size of the

grounding-electrode conductor. The rods may be driven up

to 45 degrees from the vertical in rocky soils or buried in a

trench horizontally at least 30 inches (76 cm) deep.

Sometimes, a 20-foot (6 m) length of #4 (21 mm2) bare

copper conductor is buried in the concrete footer or slab

for the house, and serves as the grounding electrode.

Connecting the grounding-electrode conductor to grounded

water pipes, well casings, or grounded building steel is

also allowed in some cases. These requirements are code

minimums. If the installation is in a high lightning area,

much more extensive grounding systems will be beneficial.

Equipment-Grounding

Conductor Size

Overcurrent Device

Rating (A)

Minimum Equipment-Grounding

Conductor Size (AWG)

(A)15 (AWG)14

   20      12

   30      10

   40      10

   60      10

   100     8

   200     6

   300     4

I hope that this might help clear any questions about grounding, I know it made me decide to up the size of the wire I was going to use to ground my genny (if I ever get enuff time and parts to finish it)

Wired_Wrong, OKC,OK

[tecker]

 This is commonly done for service and equipment grounds for lightening arrestors

 you need to setup a ground plane with several ground rods to pickup the transient

charge that wells up from the earth as the positive charge rolls in from the atmosphere

[Jerry]

Hi Wiredwrong.

Thanks for the info. I recently installed a 40 ft metal free standing tower.

I grounded the tower to a water pipe just below the tower base. The pipe is 200 ft long at 3 ft in the ground. It only took 4 ft of wire. I used 4GA.

                               JK TAS Jerry

[Bill Kichman]

Just a little clarification, the table of ground sizes based on circuit breaker sizes is the incorrect table for electrical service ground (or your genset, whatever, a POWER SOURCE), I don't have my code book handy but you want the table listing service grounding conductor sizes BASED ON CURRENT CARRYING CONDUCTOR SIZE for the feeder leaving your genset or the utility feed.  That other table you listed is for branch circuits.  The  National Electrical Code is a bohemoth spaghetti monstrosity, difficult at first to follow, and hard to keep up with all its changes that occur every 3 years. Just note that there is a difference between service grounded conductor and branch circuit ground.  Everything after the main service disconnect switch (main breaker, knife switch, fusible disconnect, whatever) is considered a branch circuit.  The feeder ahead of that is your service conductor and its grounded conductor is sized per the ampacity of the current conductors.  Hope this little tidbit helps. Life is way too complex.  Cheers

[nack]

Understand that this is minimal requirements.  I doubt that it would meet code in any municipality, they all have their own extensions.  I also can't find my NEC, but I am pretty sure that last time a ran a service ground the NEC required a minimum of 2 earthing rods at least 6 feet distant from each other plus bonding to hot and cold water pipes.  If you live on dry or rocky soil, it is probably a good idea to add a few more rods, and/or bury them in electrolyte gel (google for half ohm ground), which is sometimes used for special equipment grounds (like the audio circuits in a recording studio or theater).  If you are planning to meet codes, it would behoove you to work from a plan that is approved by your local building authority - there may be all kinds of addendums at the local level.