slab grounding

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muskrat

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Location
St. Louis, MO
Having read all these posts, and never bonded to a footer yet, how does one tie GEC to rebar? If footings were 4 seperate ones, should I tie to all or would one do it? Since footings are for 70 ft. tower, SHOULD I tie together?
Thanx for all responses/opinions.
 
Cavie

Cavie

Senior Member
Location
SW Florida
muskrat said:
Having read all these posts, and never bonded to a footer yet, how does one tie GEC to rebar? If footings were 4 seperate ones, should I tie to all or would one do it? Since footings are for 70 ft. tower, SHOULD I tie together?
Thanx for all responses/opinions.
Click to expand...

You are not bonding a footer, you are grounding the service via the footer steel using the UFER method. If the service is on a building serving the tower use the building footer steel and you are done. If the service is on a post go to one of the tower feet and attach to it and your done. Attachment to the steel is made by any approved grounding clamp in the footer. Since the wire going to the service will be stolen before you get back to it, a rebar is usually stubed up into a hollow bolck wall, interior frame wall, basement wall. Footer steel can not be exposed or in the dirt. At this point you make an axcessible connection and go to your service.
 
volt101

volt101

Senior Member
Location
New Hampshire
250.50 Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are PRESENT at each building or structure served shall be bonded together to form the grounding electrode system
....Not where available...

Its foundation or footing
Foundation:
-an underlying base or support; especially: the whole masonry substructure of a building
-a body or ground upon which something is built up or overlaid

Just my two Lincolns...
 
renosteinke

renosteinke

Senior Member
Location
NE Arkansas
Excuse me, Volt ... but flip the page and read the exception to 250.52. The NEC specifically states that you are not required to chip apart the concrete in order to tie it in.

As to another's comment regarding the placement of the slab ... the code text does require the slab to be in contact with the ground ... and specifically excludes the slabs' use as an electrode if it is separated from the ground by, say, a plastic liner. (Let's save the 'liner' debate for another thread).
 
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volt101

volt101

Senior Member
Location
New Hampshire
Existing? The OP stated new addition.....But as far as the thread in its totality, you may be incidentally right as he was not doing a service installation. However, my post was for the sake of the later conversations. The exception applies to the already pored over electrodes of existing buildings only, as you stated, you don?t need a jack hammer to get to. It does not exempt any new ones installed in the addition if any are required. btw. you do not have to turn the page when you got a new shiny book :) Some monolithic slabs require turned down footings with rebar in it for seismic design, some put it in because of expansive soils and some just try to prevent cracking from happing under their brand new walls. See the IRC. A vapor barrier (the plastic thingy) see IRC section R506.2.3 - is required under the slab portion only.
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
jwelectric said:
Can someone post the paragraph under (2) found in 250.52 (A) (3) of the 2011 cycle?

I think it says something about footers and contact with earth.
Click to expand...

Here ya go:

Metallic components shall be encased by at least
50 mm (2 in.) of concrete and shall be located horizontally
within that portion of a concrete foundation
or footing that is in direct contact with the earth or
within vertical foundations or structural components
or members that are in direct contact with the earth.
If multiple concrete-encased electrodes are present at
a building or structure, it shall be permissible to bond
only one into the grounding electrode system
 
S'mise

S'mise

Senior Member
Location
Michigan
I'm not up on the 2011, But seems like comon sense stuff.

I agree with Cavie who said " It is not the slabs or footers that are being grounded. It is the services that are being grounded using the UFER method. The old service is already grounded and needs nothing more. No UFER grounding is required for the addition. A new service being built on an old house also does not require UFER grounding." (Not if its burried)

If the existing service has been aproved, it seems superfluous to keep adding to the GE system.
 
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