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-   -   Grounding Cable (http://www.diychatroom.com/f18/grounding-cable-7835/)

Sammy 04-16-2007 06:02 PM

Grounding Cable
 
I'm getting ready to install my weather station on a brick chimney
[think old time tv antenna type install]

I would like to run the lightning grounding wire around the soffit about 20 feet to a point where I can install the ground rod without having to bore thru the new pool patio concrete. The cable may be exposed to sunlight and obviously will need to be sheathed since it will be in contact with the house.

Any suggestions on cable type for this application and conductor size solid/stranded?

Thanks

joed 04-16-2007 06:20 PM

If the weather station has power going to it, the ground should be connected to the grounding system already in place on your house.

jwhite 04-16-2007 06:20 PM

does this thing do any communications or does it just look like something that does?

The only code I can find is for radio and tv receiving equipment.

Number 10 run at streight as possible to the ground rod, and number 6 from that ground rod to the rest of the ground rods for the electrical service.

Sammy 04-16-2007 07:00 PM

It will have low voltage power to it. My concern is from a direct lightning strike to the metal pole it will be mounted on.

gregzoll 04-16-2007 08:32 PM

You will have to mount a ground rod in dirt, not through Cement. That means, either cutting a fair size square chunk out, or runing the cable a distance. This also means, not running the ground wire back into the house, which is a big no-no.

Speedy Petey 04-16-2007 09:03 PM

Greg, while the letter of the code does say the entire 8' length of the rod shall be in contact with the "soil" I don't think anyone would complain about drilling a 5/8" hole in concrete and driving the rod through.

If an inspector told me to chop out a swath of concrete to sink an almost useless ground rod I'd find another inspector.

gregzoll 04-16-2007 09:10 PM

The whole reasoning, is because Cement can contain conductive materials such as ores and rebar, which can contact the Grounding rod, rendering it useless. That is why a section about 1-2' should be cut as a square or such to allow for no contact with the materials in a slab.

Speedy Petey 04-16-2007 10:02 PM

Quote:

Originally Posted by gregzoll (Post 41270)
The whole reasoning, is because Cement can contain conductive materials such as ores and rebar, which can contact the Grounding rod, rendering it useless. That is why a section about 1-2' should be cut as a square or such to allow for no contact with the materials in a slab.

WHAT???
That is an interesting story. "Rendering it useless"?
I wonder if you have any documentation supporting this? I mean you didn't just make it up, right?

Have you ever heard of a Ufer? Also known as a "concrete encased electrode".

2' square huh? All I can say is wow!

gregzoll 04-16-2007 10:43 PM

Yes, but the use of the Ufer grounding system is debatable, due to in order for it to work effectively, the grounding system has to be done by specs, and most concrete pours for the typical home will not conform to the criteria.

In all reality, this thread can lead into debates as to what is by code, and what is in Theory.

jwhite 04-17-2007 04:28 AM

Quote:

Originally Posted by gregzoll (Post 41270)
The whole reasoning, is because Cement can contain conductive materials such as ores and rebar, which can contact the Grounding rod, rendering it useless. That is why a section about 1-2' should be cut as a square or such to allow for no contact with the materials in a slab.

How can conductive materail render a ground rod useless? Isnt the idea to drive it into conductive material? And if a concrete encased electrode is allowed why not one that is in 4 inches of concrete and the rest dirt?

Speedy Petey 04-17-2007 06:18 AM

Quote:

Originally Posted by gregzoll (Post 41274)
Yes, but the use of the Ufer grounding system is debatable, due to in order for it to work effectively, the grounding system has to be done by specs, and most concrete pours for the typical home will not conform to the criteria.

Debatable? Then WHY did they make it mandatory in the latest edition of the NEC???
If there is rebar it MUST be used as a grounding electrode.


Can you elaborate as to "most concrete pours for the typical home will not conform to the criteria"? I am very curious about this.

gregzoll 04-17-2007 07:29 AM

Unless the pour calls for it, a typical home slab will not have any rebar in it, and it will not meet the specs for a commercial structure. Also, most home builders will find short cuts to make sure costs are lower, and return is higher.

Speedy Petey 04-17-2007 07:41 AM

Of course the slab won't but what about footings? Even a monolithic slab will have rebar in the footing portion.

Quote:

Originally Posted by gregzoll (Post 41292)
Also, most home builders will find short cuts to make sure costs are lower, and return is higher.

This is not nearly always the case. At least not with the guys I work with. If you do tract and spec homes all day maybe.


BTW Greg, what is your trade?

Sammy 04-17-2007 05:51 PM

Uh Hmmmmmmm..

This tangent is starting to look like a side bar at the O. J. trial...

There is no rebar in the concrete. Fiberglass pool twenty feet away that is bonded.

I dont PLAN on going thru the concrete which is the reason for running the cable thru the soffit to a point it can be dropped down to bare ground.

My original question was as to a suggested conductor type, gauge, and sheathing.

Speedy Petey 04-17-2007 06:30 PM

As far as grounding your dish to an electrode I would follow whatever the MFG suggests. I'm sure there is info in the manual about this.
Some I have seen suggest a #10cu, and this is the NEC minimum. I'm not sure how effective this would be as far as a lightning strike is concerned though.
If you do sink another electrode it MUST be bonded to the house's GES (grounding electrode system) with at least a #6cu wire.

See NEC 810.21 regarding grounding antennas.


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