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  #1   IP: 64.242.197.254
Old June 21st, 2005, 05:16 PM
bobm bobm is offline
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Default Grounding concrete Slab

Hi All,

I am going to pour a 24x24x7" concrete slab in front of my garage as a mini drive way. The slab will have wire mesh in it. How can I best ground the slab or should I not worry about it?

I had a pretty nasty strike last year when I was building the garage. I have always wondered if my garage floor had something to do with it. The lightning hit a tree about 100' away from the garage, dug a 6" trench to the corner of the garage, burnt a few floor joists and knocked out both garage door openers. BTW, the garage door openers were not even plugged in, rough wiring had not even started!

Thanks

Bob
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  #2   IP: 66.59.122.85
Old June 21st, 2005, 05:52 PM
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mdshunk mdshunk is offline
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I certainly wouldn't worry about it unless there will be livestock standing on the concrete pad.

Nothing would have helped in the face of the lightning strike you describe.
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  #3   IP: 64.242.197.254
Old June 21st, 2005, 06:12 PM
bobm bobm is offline
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thanks MD,

I thought I remember reading a year or so back about wire mesh or rebar in slabs needing to be grounded. Something that may be introduced in future code??? bob
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  #4   IP: 66.59.122.85
Old June 21st, 2005, 06:31 PM
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Quote:
Originally Posted by bobm
thanks MD,

I thought I remember reading a year or so back about wire mesh or rebar in slabs needing to be grounded. Something that may be introduced in future code??? bob
Yes, new construction needs the rebar in the footers connected to the ground buss in the panel. Concrete driveways are excluded except in agricultrual areas where the livestock stand or walk across them.
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  #5   IP: 64.242.197.254
Old June 21st, 2005, 06:36 PM
bobm bobm is offline
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Why just the footers and not the walls? Does the inspector actually look for this. I would love to know the safety issue here, the footer is usally buried in the ground anyway?

thanks

Bob
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  #6   IP: 66.59.122.85
Old June 21st, 2005, 06:39 PM
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Quote:
Originally Posted by bobm
Why just the footers and not the walls? Does the inspector actually look for this. I would love to know the safety issue here, the footer is usally buried in the ground anyway?

thanks

Bob

You're not really "grounding" the footer. You're using the footer as a grounding electrode. A 10 foot piece of rebar in the concrete footer issuperior to a couple of ground rods hammered in the ground. This footer ground (sometimes called "Ufer ground", after the man that invented it) does nothing to make the footer safer. It's just using the properties of the steel in the buried concrete to make a good earth contact.
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  #7   IP: 64.242.197.254
Old June 21st, 2005, 06:41 PM
bobm bobm is offline
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Right! Thanks bob
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  #8   IP: 69.148.244.212
Old June 21st, 2005, 07:05 PM
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Quote:
Originally Posted by bobm
thanks MD,

I thought I remember reading a year or so back about wire mesh or rebar in slabs needing to be grounded. Something that may be introduced in future code??? bob
Actually it is the oposite.

The rebar in footing can be the ground electrode. It is called a ufer ground.
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