Slab with rebar or wire mesh?

[cajun1]

I'm getting a slab poured soon for my brand-new Epic, set to arrive next week!  The guy is using a heavy-guage wire mesh instead of rebar.  Is this okay?  Also, I read something a while back about grounding a slab.  Is that necessary?  I don't think he's doing that.
Thanks in advance!

[Chas]

I have used welded wire mesh successfully for years.

I have contractors who only use rebar.

Both seem to work just fine - but I am not a specialist in this.

As to bonding - it is very easy: just put a bonding clamp and some wire on the rebar and run it to wherever it makes sense. Or, drill a hole in the forms and put a grounding rod so that it sticks out slightly. I have even seen people leave a section of rebar sticking out, but that rusts off pretty quickly so I don't recomment it.

You shouldn't have to worry about it, but doing it now is sure a lot easier than drilling in and adding it later.

And you would be amazed at how conductive a damp concrete slab is...


 8-)

[cajun1]

Ok, is the grounding just for spa slabs?  Because I have a concrete patio and I don't see anything sticking out from it.

[Dr. Spa™ Ret.]

Rule of thumb is if it's under 6" thick, wire. Over 6" rebar. Thin concrete with rebar tends to crack along the rebar.

It should also be noted that rebar and welded wire mesh are not to PREVENT the concrete from cracking, but to prevent vertical movement of the concrete when it does crack.

[cajun1]

mine's going to be 4 inches, so I guess wire is the way to go, then.

[jeff925]

i would ground(bond) the slab. all you have to do is take some wire, something large like #8 or #10, strip about 12 inches or so from it, and wrap it several times tightly around if the rebar or wire mesh and leave some hanging out after the concrete is poured. Then drive a ground rod next to the pad and attach the ground wire to it.

[bluesman]

I just had my slab poured last Friday. My contractor used rebar and wire mesh. We also used 3500 psi concrete. The slab is 18 x 20 x 6" thick. My tub is going to be installed next Thursday 3/8.

Bluesman 8-)

[cajun1]

Bluesman, did they ground (bond) your slab?
Mine is only going to be 8 by 10.

[96SC]

i would ground(bond) the slab.  

   As I have said in the past, I am amazed at the things I have learned about hot tubs in this forum.  Never, ever have I heard or read about grounding (I guess bonding is the technical term) a patio that a spa is being put on.

Thanks again.

[bluesman]

The spa is grouned back to the main panel. There's a 50 amp disconnect 5 feet away from the spa which has #6 four wire (black,white,red and green wires) that back to the main panel in the house which is grouned. Since the disconnect goes back to ground via #6 four wire to the main panel ground, it is not necessary to ground again at the spa location.

Bluesman 8-)

[bluesman]

I think the "d" key is sticking.

[cajun1]

Bluesman, that's what my husband told me.  We're going to have the disconnect bax and the #6 four wire, too, going to the main.  So I guess we're okay if we don't ground the slab.
Thanks
BTW, what tub are you getting?

[Brewman]

Grounding the slab is a NEC code issue, which may or may not be enforced in your area.  When I wired my spa I wasn't required to bond the slab- that was 3 1/2 years ago.  Check with your local code enforcement people if you're worried about this, if your DIY.  Contractors should know the local rules if your going that route.
 

[svspa]

Guys,

I think you should clarify you're talking about 2 different things. Grounding and Bonding are different.

Here's a link that explains some of it. From what I remember of my tub install there should be a bonding lug in the hot tub cabinet and that's where any metal within 5' of the tub should be bonded.

[link]http://ecmweb.com/mag/electric_grounding_vs_bonding_11/index.html[/link]

I am not an electrician though so I take no responsibility for anyone frying themselves, their hot tub, their home electrical system or their cherished pets.

Steve

[Chas]

We have two terms here which are not equal. As the terms apply here:

Bonding is simply connecting two things together.

Grounding is connecting something to the ground conductor in your electrical system.

So to bond your slab, you could run a wire from the slab to the bonding bus on your spa. That ties the two items together electrically. Metal objects anywhere near a tub are supposed to be bonded - patio covers, fences, equipment, electrical conduit, lighting fixtures etc. I have been forced by inspectors to bond aluminum window frames right next to a tub, and let me tell you: there is no 'pretty' way to accomplish that one!

To get a wire into or from your slab, you can do what has been suggested here: run a wire into the rebar or ww before the pour, or simply set a copper ground stake into the form with the end exposed somehow. I like to drill a hole for it hrough the form so that they are not sticking straight up, but YMMV.

The spa should be grounded, so if you bond items to it, they become grounded as well. But even if the ground to the tub is somehow broken, having everything around the tub at the same electrical potential minimizes danger of zappage.

The point of bonding is that if you ground the tub, that ground conductor could be real long as it makes it's way back to the box. If you ground the slab the same way, there could still be a lot of potential difference between the slab and the tub. By running a short bond wire right from the slab to the tub - or right from the metal post or what-have-you to the tub - you cancel out any potential difference between the two.

'Potential Difference' is roughly equal to voltage, and it is what you feel if you cross two live wires.

 8-)