Ribar in Concrete

[IBinit4fun]

What a great Forum! I've been following along for about a year. You guys helped me choose the right tub for wifey and me...Marquis Euphoria. We've had it since 3/1/04 and love tubbin'. I finally thought of a question that I haven't seen posted. I originally poured my 8X8 pad with fiber and no ribar. No problems. But now I need to move the tub because we decided to put a door where the dining room window is and the tub needs to move over a couple of feet. Therefore, I have to increase the size of my pad by a couple of feet on one side. I drilled into the side of the existing pad and drove in ribar to tie to the new concrete. But I remember reading somewhere a while back something about needing to ground ribar back to the main panel for some reason. Since I didn't originally use ribar, I didn't give it any thought and can't remember where I read it. But now...? Has anyone ever heard of this? I am handy and do my own work. I follow code, but could not find this in NEC or local code. I know you guys will have the answer. Happy tubbin'. Thanks...Rick

[cparlf]

For what it's worth, I had my slab (11.6 x 11.6) with an apron extending to join my existing patio poured last Saturday.  I had 5 inch; 4,000 psi concrete, with a 4 inch stone bed.  I did not ask for rebar, but there is a heavy wire grate laid on top of the stone.  I too was curious about the previous mention of grounding, but my licensed, union electrician said grounding was not necessary given the requirements for the GFI and shut off access etc.  Hopefully I am not in risk with this, the electrician has wired a lot of these and I have not read any stories in the papers yet.......And he charged no additional for a 60 vs 50 amp, says there is not cost difference.

As a side note, this is truly back breaking work.  My contractor, a young man late 20's essentially collapsed after completing the job from heat stroke.  I had provided cold water, iced tea and wet towels for him, all day, but I guess in his effort to finish this slab before the crete settled, he worked through the symptoms.  2.5 days in the hospital later he is thankfully OK.  If you are having this work done in this summer heat, remember to be aware of the dangers for these people.    

[Shut_Down_Stranger]

I do not think that you have to gound the tub to the rebar.

I put in concrete 5 inches thick, 3/8" rebar on 2 foot centers just as additional insurance. The concrete guys said it was a good idea.

the link below is what it looked like.

http://members.cox.net/jim69bird/Preparation

[UnderTheStars]

Hi IIBinit4fun!  I'm the one who mentioned grounding the rebar - sorry for not responding sooner, was out of town a couple days and the last 24 hours I was taking delivery of our new hottub (finally!)

Here's the straight scoop on grounding rebar:  First, I think most manufacturers recommend that metal re-inforcement in the slab (or any metal within 5' of the spa) be grounded back to the panel.  I know for a fact that HotSpring states this is should be done and they provide a connection in the equip. area to ground it to.

Secondly, why?  It has to do with how breakers work and why they trip.  Any metal close to a 230 volt spa is a POTENTIAL conductor (particularly if in contact with the ground.)  If the metal conductor does become energized, current will flow (through the ground, through you, etc.)  If the energized conductor is grounded back to the panel the breaker will trip.  It it is not grounded, the breaker will not sense the "ground fault" and may not trip. . .that means the juice continues to flow - not good if it flows through you.

Ok, so how can the rebar in concrete get energized?  Most common (though it's rare) is due to a short - loose wire or water gets into the equip. area (water is a conductor.)  In either case, if the crete is damp, the current may energize the rebar & slab.  Step onto the damp concrete with wet feet and you may become very interested in whether or not the breaker will trip!

Is this scenario likely?  NO.  If it does happen will you care?  Probably.  So why would an electrician say this is not needed?  Well, electricians are mere mortals and do make mistakes.  Particularly "old school" who cut their teeth on knob & tube wiring which was an un-grounded system.

I can't tell you how many "bootleg grounds" I've corrected that were installed by "qualified electricians."  (Bootleg ground means not running a third ground wire back to the panel.  The logic is, the white wire goes to the same place at the panel so save wire by just running a white & black and then jumper the white/neutral to the grouning lug of  the outlet or wall switch. . .It doesn't work and can cause "shocking" results.

Look, not trying to start an arguement, just trying to answer your question.  The circumstances when you would need the rebar grounded are admittedly rare and may never come up.  However, if you do your own slab prep, you are talking $2 worth of #8 solid copper grounding wire and a $2 connector (use an "acorn nut" to bond the wire to the rebar grid. . .just make good tight twists with the tie wire when you form the grid.)  Pretty cheap insurance. . .I grounded mine.

sorry for the long answer, electrical stuff can be complicated - enjoy your tub!