Slab with rebar or wire mesh?

[Dr. Spa™ Ret.]

I think there also some other confussion here. The rebar / wire should be BONDED to the spa system. It should NOT be grounded through a grounding rod. Doing so can actually be dangerous.

[Brewman]

Nice catch- I meant bonding in my post.  Just a mental oops.  

[autoplay]

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.

Correct you are Dr. Spa  The aggregate,the moisture,and the mix over-all play a key part in the successful curing of concrete/portland based products.

Tile/stone mason specs.....can use 2"x2" wire,up to 4"s thick.

In a frost/freeze enviroment....I would highly recommend a free-floating slab. If that's not do-able,you want expansion joints,outside,every 16'. If tying into an existing slab,bore/core into existing,tie in with rebar,and use expansion felt etc at the tie-in.  Your concrete contractor will know the specs for your area.

GL

[morecowbell]

Definitely check with your local code enforcement official.
Here in New Jersey a new ordinance will be in effect requiring what is called an equipotential bonding grid on concrete slabs for spas as well as concrete decking surrounding in ground pools. This requirement will probably mean an addittional $350 to a homeowner. That is if it is done correctly. If it is not correct they will make you rip it out and do it over. We are a heavily regulated state however.

[Gomboman]

I'm confused on this matter myself. Our spa was installed on a concrete patio that was built a few years prior to getting the spa. I don't believe the patio was bonded or grounded in any official manner. I know the spa has a grounding wire installed within the cabinet. Should I be concerned with this? Is it possible to ground the patio now after the fact? There is no wire mesh or rebar buried in my concrete.

[Dr. Spa™ Ret.]

First off, BONDING and GROUNDING are two VERY different things, for VERY different purposes.

If the "grounding wire inside your cabinet" is visible (not inside an electrical box), it is NOT a grounding wire, but is a BONDING wire (or "lug").

Again, bonding and grounding are DIFFERENT. HEY, they're even spelled differently. The very simple explanation of bonding is that it is done to prevent you from being shocked when your left hand touches one metal component, and your right hand touches another metal component. By running a wire from one component to another, stray electricity (from a short for example) will equalize through the wire and one metal component will NOT have a greater voltage in it than another component.

Grounding on the other hand is to give stray electrical current a place to go, other than through you (and in theory it goes with such "force" it causes a breaker to trip or a fuse to blow).

To some extent, the two work in conjunction with each other, sort of as backups for each other.   BUT THER ARE DIFFERENT.

Lets take a real life example (happened to a customer of mine when I was a lowly repair man). A guys spa is not properly grounded. The heater shorts out. When he stands on the wet concrete by his spa, and sticks his hand in the water electricity from the shorted heater travels through the water, through his hand, down through the concrete into the earth. He gets a nice little shock. Had the pad been BONDED to the spa the electricity in the water would have also been in the concrete pad. AND the amount of electricity in each would have been EQUAL. and he wouldn't have felt a shock. Had his spa been properly GROUNDED (he did his own wiring job), the ground wire would have given the "stray electricity a path to go and almost certainly would have tripped the circuit breaker. Even if it didn't trip the breaker, electricity "takes the path of least resistance", and since it travels more easily through the ground wire than through the human body, he wouldn't have gotten shocked.

Now, had he GROUNDED the pad (attached it to a metal rod driven into the ground), he probably would have felt a much more severe shock as the electricity would have been able to travel through the pad to earth more easily.

Furthermore. According to the NEC, you CAN NOT use a "grounding rod" ("bonding rod" actually) as a ground (if, I believe, the voltage is under 600 volts). Dirt, is a VERY POOR conductor of electricity. In reality what this will do is potentially electrify the ground around the spa and has the potential of ELECTROCUTING you if your standing on the ground and touch something that IS properly grounded (electricity in the electrified ground travels up through you and out to what your touching that's properly grounded). There's actually a documented case of this happen at a fish farm in the UK. The little fishies were periodically being electrocuted from an improperly grounded/bonded power line TWO MILES AWAY.

So Gomb, should you bond your spa to the pad? Well, it could be done if you can get to the metal reinforcement. But is it really necessary? Up until a couple of years ago it wasn't a requirement of code. Since your pad was pre-existing, it's not required (unless you have some very weird municipality requiring it be brought up to current code if a spa is put on it....... VERY unlikely). Personally I wouldn't bother.

OH, also, somewhere someone mentioned all "you" had to do was wrap a wire around the metal reinforcement to effective bond it. THIS IS ABSOLUTELY INCORRECT. The bonding wire HAS to be attached permanently and solidly. Generally with a clamp. "Wrapping it around" does not give a solid connection.

Please email me and I'll now give you the written test on bonding vs. grounding. Remember, eyes on your own papers. Recess when you're done.  

© 2007 Dr. Spa

[Dr. Spa™ Ret.]

holly crap. I typed all that?

[Chas]

Who is this 'Holly" Chick?

 8-)

[Dr. Spa™ Ret.]

Who is this 'Holly" Chick?

 8-)

Terms next "spa technician"?

[Gomboman]

Very nice doc. Thanks for the lesson.  

[Dr. Spa™ Ret.]

After receiving your email this morning (and responding), let me try a more direct answer to your question about "grounding" the slab.

To be technically correct, and up to code what should be done is as follows.... A copper wire (I believe #6) should be firmly attached to the reinforcement wire mesh. This copper wire should extend up through the pad. On the underside (or side) of the control box for the spa (see picture #1 below) there should be a bonding lug or bar (should look similar to picture #2 or #2a). This "bonding lug should be clearly visable without having to open the control box. The copper wire should be attached to the "bonding lug". Please note there may and probably are other bare coper wires running to this lug/bar. Most frequently one from the pump. Each wire should go into a seperate hole in the bonding bar.


#1 - control box


#2 - bonding lug


#2a - bonding lug

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!

[cool breeze]

Dr. spa help me understand this
 you said Dirt, is a VERY POOR conductor of electricity. In reality what this will do is potentially electrify the ground around the spa and has the potential of ELECTROCUTING you if your standing on the ground and touch something that IS properly grounded
i thought a proper ground is a copper grounding rod  around 7' long driven into the ground (dirt) which you would connect a #6 copper  ground wire to

[Dr. Spa™ Ret.]

I'm not sure how to additionally help you. You thought a proper ground is a copper grounding rod  around 7' long driven into the ground. I've explained why this is incorrect. I can though add that grounding through the use of grounding rod is typically ONLY done at the main electrical panel is done to limit the voltage imposed on the system ("system" being the electrical company providing the electricity) by lightning, unintentional contact with higher-voltage lines, or line surges.

[Brewman]

A grounding rod is not allowed by NEC for most slave (sub) panels.  A spa panel in this case counts a sub panel.  A seperate ground rod here wouldn't be allowed per NEC.  If you want to argue the case with them, be my guest.  It's your spa.

 If the sub panel is being installed in a building that is physically disconnected including any conductive materials like metal pipes, etc.., then a seperate ground rod for that sub panel may be required.  

For most spa installs, if not all of them, no ground rod allowed.  A correctly installed spa and spa panel will GROUND back to the main panel ground bus, which is connected to the spike in the ground.

You need to BOND any grounded metal that is within 5' of the spa, to the spa.  As explained earlier, this is not grounding, but bonding.  When I did my spa wiring I was required to bond my water spigot to the spa bonding lug with a bare solid copper #6 awg bonding wire and a bonding clamp on the spigot.  This bare wire runs outsid of the wire bundle conduit- attached with zip ties.  Rules might be different now on what wire is required to bond.

As always, if in doubt check with your local authority for what is required in your area.  NEC code is interpreted in various ways, what flies here might not in your area.

[Bama]

OMG, I didn't know you had to ground any metal near a hot tub??
I've recently put a patio cover over my tub.  
What should I do to ground that?