[TowerTalk] Another Grounding Question

[Jim Lux]

On 9/7/12 8:19 AM, Marshall Stewart wrote:
> In the interest of safety, before you decide to dig to look for a buried
> ground rod at the pole mounted meter or drive an additional ground rod, you
> should have the exact location of the buried power cables clearly marked by
> one of those "call before you dig" services.  Your power company or co-op
> may be able to mark the cable location for you.
>
> Then if it were mine, I'd want to verify that there really was a ground rod
> at the base of the meter base pole and that the bare copper wire you
> described running down the pole was connected to a ground rod with a good
> electrical and mechanical connection.

Or, maybe, it's just a bare copper wire wrapped around the bottom of the 
pole.  That probably works just as well as an actual rod. The diameter 
of the rod doesn't affect the ground resistance all that much: NEC 
requirements on rod diameter are more about mechanical properties for 
pounding the darn thing in.

Bear in mind that power poles are NOT subject to the NEC (the NEC sort 
of stops at the utility demarcation)... the utility gets to make it's 
own rules (which, in theory, probably hew to industry standards like 
IEEE 142)



  Then I'd add a ground rod just
> outside your basement wall close to your loadcenter and run no smaller than
> a #6 solid copper wire from the ground bar in the loadcenter to the ground
> rod just outside the basement wall and then to the ground rod at the base of
> the meter pole.  Then you would know for sure the meter socket base, the
> loadcenter ground bar, and the 2 ground rods were all solidly bonded
> together.

is the feeder run from the pole with the meter above or below ground?

In general, you don't really care much about whether the utility is 
properly grounded:  Your grounding design should assume it's not. And 
you might not want to "help" the utility here, especially if you share a 
transformer with other customers, because your ground wire might wind up 
carrying their fault current.  (sort of the open neutral problem in a 
different form..).   They will likely ground the centertap of the low 
voltage winding to limit the voltage (the HV primary is floating, and if 
you don't ground something on the secondary, unequal capacitive coupling 
will tend to float the secondary up), but it's not really intended to 
carry significant fault current.

The "ground" in your house, on the other hand, *is* intended to carry 
significant fault current:  if a line/chassis-ground short occurs, you 
want enough current to flow to trip the breaker, quickly, so you don't 
have an MGM-Grand scenario.  Note that the electrical safety ground 
could do this function if totally isolated from earth.  The second 
purpose of the green wire ground is to make the voltage on the chassis 
(things you touch) close to the voltage at your feet.  That's why you 
need a grounding electrode. But for that purpose, you can actually ahve 
a fairly high resistance.


Ultimately, you want to make sure that there is only one place in the 
system where "neutral" and "ground" are connected together. All the 
"grounds" bond to the ground, and nowhere else.


  There are two classic errors that violate this principle.. bonding the 
neutral and greenwire ground in a subpanel.. There's a jumper in the box 
that isn't removed; and separately grounding the chassis of a *portable* 
generator that's connected as an emergency power source to an existing 
system.  (portable generators usually have chassis and neutral bonded... 
fine if all your loads are portable and running off extension cords. 
generators intended for permanent installation have neutral and chassis 
separate)



>
> There are those on this reflector with considerable knowledge on this
> subject, and they may have other and better suggestions.
>
> 73,
> Marsh, KA5M
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Gary
> "Joe" Mayfield
> Sent: Thursday, September 06, 2012 10:45 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] Another Grounding Question
>
> I need to make one more grounding connection by bonding the tower grounds to
> the electrical ground.
>
>
>
> My power meter is on a light pole about 20 feet from my house.  The power
> comes to the pole underground and then goes to the house underground as
> well.  It just pops up out of the ground for the light and then the meter.
>
>
>
> The power enters the house through a basement wall.
>
>
>
> There is no obvious ground rod to be seen.  The pole has a bare wire running
> from the meter into the ground.  I suspect it is attached to the bottom of
> the pole.  If I bond the tower grounds to this wire have I done what I am
> supposed to do?  If not what do folks suggest?
>
>
>
> Thanks and 73,
>
> Joe kk0sd
>
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