To Bond Or Not To Bond

[LucyMarin]

So, we're moving forward on a small concrete slab for our Marquis Spirit. I've asked my contractor to install a bonding wire attached to the rebar, however, my electrician is telling me that this is not necessary. He says for a portable spa such as this the bonding wire is not really required as no metal parts of the spa are in contact with the concrete, rather it's encased in a plastic / synthetic case etc. The spa will of course be hooked up to a dedicated GFCI. At any rate, everything I read on-line seems to contradict what my electrician is telling me. There is no metal or any other water within 5 feet of the tub. The electrician has done hundreds of spa hook up's as this is is specialty and I do feel very comfortable with him, but am curious as to anyone's experience and/or comments on this matter. If I do have the contractor install a bonding wire, where should I have it leave the concrete? The slab is exactly the same size as the tub. Thanks in advance for your comments....

[Dr. Spa]

The requirement depends on your municipality and what year NEC they've adopted. The bonding of the rebar is a rather new code and many municipalities are years behind, not yet adopting this code.

Whether or not any metal is touching the pad is irrelevant. The purpose of bonding is to prevent you from being shocked/electrocuted when your left hand touches one metal component, and your right hand touches another metal component (or in this case your foot). Conceivably, if there were a short somewhere, AND a fault in the main grounding, and you touched something electrified, the current could travel through you, through the concrete pad to ground, and electrocute you (I've actually seen this happen, to an extent....no one died, but there was a noticeable shock). The bonding wire would "neutralize" the pad preventing a shock

[LucyMarin]

The requirement depends on your municipality and what year NEC they've adopted. The bonding of the rebar is a rather new code and many municipalities are years behind, not yet adopting this code.

Whether or not any metal is touching the pad is irrelevant. The purpose of bonding is to prevent you from being shocked/electrocuted when your left hand touches one metal component, and your right hand touches another metal component (or in this case your foot). Conceivably, if there were a short somewhere, AND a fault in the main grounding, and you touched something electrified, the current could travel through you, through the concrete pad to ground, and electrocute you (I've actually seen this happen, to an extent....no one died, but there was a noticeable shock). The bonding wire would "neutralize" the pad preventing a shock

My town follows the Uniform Swimming Pool, Spa and Hot Tub Code, 1997 edition, published by the International Association of Plumbing and Mechanical Officials. There's a copy at the building department and I'll take a look at it. That aside, you're basically telling me that it's a good idea to have a bonding wire installed for the obvious reasons. What if I was installing the tub directly on the ground or on pea gravel? Would a bonding wire then also be recommended or is this more related to my choice of installation? thx

[Dr. Spa]

1997 the code didn't yet exist, so you're probably not required to bond the rebar.

There's a second, somewhat opposite reason for it as well. In very rare instances it's possible for the utility company to have a current leak from their equipment. Happens very rarely with ground level transformers. Current leaks from the transformer "electrifying" the ground. If you were to be touching the electrified ground (especially with bare, wet feet), and touch a properly grounded metal object, conceivably you could receive a shock. Directly on the ground would be less of an issue as the metal rebar in concrete creates a larger "grid" to "capture" more of the electricity.

[hot_water]

Hi Lucy,

There area many local areas where the "equipotential grid" requirement is not being enforced, either because the requirement hasn't been adopted or because it's just being ignored by the local officials. This lack of enforcement is potentially a good thing if a person wants to install a tub on an existing slab, since, best case it's painful to install the bond after the slab is poured and worst case, you have to tear the slab out. There are some ways to legally skirt the requirement even if it IS being enforced for existing slab installations, but not for free.

The motivation for the grid requirement is stray voltage, not ground faults. One scenario is standing outside the tub on the ground where stray voltage is present. If you touch the water, which is bonded back to the main panel and therefore possibly at a different potential than the ground, there can be a current flow through your body. In your case... if you are really interested in meeting the National Electrical Code requirement, I suggest that you look over the actual code sections. As I recall, the equipotential grid needs to extend to the area around the spa where people can stand (the dimensions are in the code). Since you indicated that your concrete is the exact size of the tub, you might well need something beyond just bonding the rebar.

If you have a metal part in your spa that has become shorted to voltage (typically something like the light fixture) and your body touches it, the GFI will trip. If the GFI is bad or the installation is improper, the equipotential grid is unlikely to save your bacon. The sad fact is that in the case of you being in the spa and touching a part that has become shorted to voltage... unless your GFI is working, you are going to be in a world of hurt, bonded grid or no.

Test your GFI often. GFIs can and DO go bad. Your safety relies on it working.

Getting back to the grid.... in your case, since you're putting in a new slab with rebar, IMO it makes absolutely no sense at all not to install the bond wire. For a new slab it's not difficult or expensive, it will protect you in the future should you upgrade or otherwise need to re-install the spa and the local authorities get sticky about re-inspecting. Personally I don't stay awake at night worrying about stray voltage, but if I was pouring a slab today I would not spend more than 1 millisecond thinking about it - I would just do it. In fact, I would bring out a couple of bonding wires in a few locations.... just because it's easy. You never know when you may want to re-orient your spa on the slab to suit a yard makeover or whatever.

As a minimum, if you don't want to pay the electrician to come out, ask the concrete people to bring at least one rebar out of the edge of the slab on each side. Again, it's easy to do, and it allows you to get to the rebar easily.

[LucyMarin]

Hi Lucy,

There area many local areas where the "equipotential grid" requirement is not being enforced, either because the requirement hasn't been adopted or because it's just being ignored by the local officials. This lack of enforcement is potentially a good thing if a person wants to install a tub on an existing slab, since, best case it's painful to install the bond after the slab is poured and worst case, you have to tear the slab out. There are some ways to legally skirt the requirement even if it IS being enforced for existing slab installations, but not for free.

The motivation for the grid requirement is stray voltage, not ground faults. One scenario is standing outside the tub on the ground where stray voltage is present. If you touch the water, which is bonded back to the main panel and therefore possibly at a different potential than the ground, there can be a current flow through your body. In your case... if you are really interested in meeting the National Electrical Code requirement, I suggest that you look over the actual code sections. As I recall, the equipotential grid needs to extend to the area around the spa where people can stand (the dimensions are in the code). Since you indicated that your concrete is the exact size of the tub, you might well need something beyond just bonding the rebar.

If you have a metal part in your spa that has become shorted to voltage (typically something like the light fixture) and your body touches it, the GFI will trip. If the GFI is bad or the installation is improper, the equipotential grid is unlikely to save your bacon. The sad fact is that in the case of you being in the spa and touching a part that has become shorted to voltage... unless your GFI is working, you are going to be in a world of hurt, bonded grid or no.

Test your GFI often. GFIs can and DO go bad. Your safety relies on it working.

Getting back to the grid.... in your case, since you're putting in a new slab with rebar, IMO it makes absolutely no sense at all not to install the bond wire. For a new slab it's not difficult or expensive, it will protect you in the future should you upgrade or otherwise need to re-install the spa and the local authorities get sticky about re-inspecting. Personally I don't stay awake at night worrying about stray voltage, but if I was pouring a slab today I would not spend more than 1 millisecond thinking about it - I would just do it. In fact, I would bring out a couple of bonding wires in a few locations.... just because it's easy. You never know when you may want to re-orient your spa on the slab to suit a yard makeover or whatever.

As a minimum, if you don't want to pay the electrician to come out, ask the concrete people to bring at least one rebar out of the edge of the slab on each side. Again, it's easy to do, and it allows you to get to the rebar easily.

Thanks much for your comments. Can I have the bonding wire come directly through the concrete? i.e. I don't think it needs a conduit?

[NewB@Spa]

Lucy...I had the same predicament. My muni requires concrete pad be bonded. Unfortunately my pad is over 30yrs old and bonding is not an option. I opted for the plastic spa pad (~$275) right on my concrete. My muni allows it and 6+ months (through winter) and never had a problem. One additional benefit is that when you set down your tub, if it is not oriented the way you like it is very easy (with 2 people) to spin the tub.

[hot_water]

Lucy,

NewB's solution is a good one as long as it makes his inspector happy. I'm not sure that the use of the spapad will be universally accepted... code says you can install on wood, though - so a layer of deck boards on the concrete should pass. In any case this is only relevant to existing pads. Since you're pouring a new one, you should install the ground wire.

I wouldn't swear to it but I'm pretty sure you COULD just run the wire out of the concrete! However, this would, IMO, be an amateurish installation. There's lots of better ways to do it. One easy one is to bring the wire out in a flexible metal conduit. You can use type BX for this, but I strongly recommend that you either paint the outside of the conduit or wrap it in corrosion resistant tape such as 3M Templex where it's buried in the concrete. Don't stretch the tape at the ends of the wrap or it WILL come loose! A better solution is to find TECK conduit rather than BX and avoid painting or tape-wrapping. TECK is pretty much the same stuff as BX but has an external plastic jacket. You will need to go to an electrical supply for this as I've not seen it at my local Home Depot, Lowe's or Orchard. You still should wrap the fitting connecting the wire to the rebar in tape before the concrete is poured. And do bring at least one spare wire out, in case the wire gets broken - it happens!

[pkillur]

Lucy,

NewB's solution is a good one as long as it makes his inspector happy. I'm not sure that the use of the spapad will be universally accepted... code says you can install on wood, though - so a layer of deck boards on the concrete should pass. In any case this is only relevant to existing pads. Since you're pouring a new one, you should install the ground wire.

I wouldn't swear to it but I'm pretty sure you COULD just run the wire out of the concrete! However, this would, IMO, be an amateurish installation. There's lots of better ways to do it. One easy one is to bring the wire out in a flexible metal conduit. You can use type BX for this, but I strongly recommend that you either paint the outside of the conduit or wrap it in corrosion resistant tape such as 3M Templex where it's buried in the concrete. Don't stretch the tape at the ends of the wrap or it WILL come loose! A better solution is to find TECK conduit rather than BX and avoid painting or tape-wrapping. TECK is pretty much the same stuff as BX but has an external plastic jacket. You will need to go to an electrical supply for this as I've not seen it at my local Home Depot, Lowe's or Orchard. You still should wrap the fitting connecting the wire to the rebar in tape before the concrete is poured. And do bring at least one spare wire out, in case the wire gets broken - it happens!

I used type LA because it can be direct buried or stuck in concrete if needed (http://www.powercabling.com/flexconduit.htm) I think I got it from either Lowes or Home Depot. If I recall this is a fairly small pad, so I would just pour rather than getting a spa-pad, but that's just my thought.

[LucyMarin]

Lucy,

NewB's solution is a good one as long as it makes his inspector happy. I'm not sure that the use of the spapad will be universally accepted... code says you can install on wood, though - so a layer of deck boards on the concrete should pass. In any case this is only relevant to existing pads. Since you're pouring a new one, you should install the ground wire.

I wouldn't swear to it but I'm pretty sure you COULD just run the wire out of the concrete! However, this would, IMO, be an amateurish installation. There's lots of better ways to do it. One easy one is to bring the wire out in a flexible metal conduit. You can use type BX for this, but I strongly recommend that you either paint the outside of the conduit or wrap it in corrosion resistant tape such as 3M Templex where it's buried in the concrete. Don't stretch the tape at the ends of the wrap or it WILL come loose! A better solution is to find TECK conduit rather than BX and avoid painting or tape-wrapping. TECK is pretty much the same stuff as BX but has an external plastic jacket. You will need to go to an electrical supply for this as I've not seen it at my local Home Depot, Lowe's or Orchard. You still should wrap the fitting connecting the wire to the rebar in tape before the concrete is poured. And do bring at least one spare wire out, in case the wire gets broken - it happens!

I used type LA because it can be direct buried or stuck in concrete if needed (http://www.powercabling.com/flexconduit.htm) I think I got it from either Lowes or Home Depot. If I recall this is a fairly small pad, so I would just pour rather than getting a spa-pad, but that's just my thought.

We poured a slab today and ran a bonding wire accordingly. Thanks for all the input.

[LucyMarin]

I'm very disappointed in our slab. It's not very level with a 3 inch swale (width wise, maybe 1/4 inch deep, give or take) running just off the left edge and a few other low (or high, depending on your perspective) spots throughout the slab. I expected it to be perfectly level, but such is not the case. My guess is that some of the concrete funneled out in some cracks in the stone below the ground or something of the like. My contractor is coming back out to look at it today. He made mention of adding some mortar something or other in the low spots. I'm going to ask him to pour another inch of concrete over the pad to even it out, though don't know how this will mesh with the original pad or if it will carry the strength of the slab below it. The low spots within the slab are probably ok, but the left edge is an issue certainly for potential drainage and maybe even for the integrity of the corner of the tub. It's less than a 1/2 inch, but deep enough for water to pool in the low spots. Annoyed with this spotty work....

[IDW]

I'm very disappointed in our slab. It's not very level with a 3 inch swale (width wise, maybe 1/4 inch deep, give or take) running just off the left edge and a few other low (or high, depending on your perspective) spots throughout the slab. I expected it to be perfectly level, but such is not the case. My guess is that some of the concrete funneled out in some cracks in the stone below the ground or something of the like. My contractor is coming back out to look at it today. He made mention of adding some mortar something or other in the low spots. I'm going to ask him to pour another inch of concrete over the pad to even it out, though don't know how this will mesh with the original pad or if it will carry the strength of the slab below it. The low spots within the slab are probably ok, but the left edge is an issue certainly for potential drainage and maybe even for the integrity of the corner of the tub. It's less than a 1/2 inch, but deep enough for water to pool in the low spots. Annoyed with this spotty work....

Have him remove it if your not happy. An inch of concrete is a bad idea. Concrete should always be 4 inches think.

[hot_water]

I'm very disappointed in our slab. It's not very level with a 3 inch swale (width wise, maybe 1/4 inch deep, give or take) running just off the left edge and a few other low (or high, depending on your perspective) spots throughout the slab. I expected it to be perfectly level, but such is not the case. My guess is that some of the concrete funneled out in some cracks in the stone below the ground or something of the like. My contractor is coming back out to look at it today. He made mention of adding some mortar something or other in the low spots. I'm going to ask him to pour another inch of concrete over the pad to even it out, though don't know how this will mesh with the original pad or if it will carry the strength of the slab below it. The low spots within the slab are probably ok, but the left edge is an issue certainly for potential drainage and maybe even for the integrity of the corner of the tub. It's less than a 1/2 inch, but deep enough for water to pool in the low spots. Annoyed with this spotty work....

Have him remove it if your not happy. An inch of concrete is a bad idea. Concrete should always be 4 inches think.

I agree with IDW. Don't pay him. You contracted for usual and customary workmanship and what you described isn't that.

Adding another layer of concrete is a bad idea. Concrete doesn't bond reliably well to itself. There are self levelling concrete products out there, but I don't trust them in the weather. They are usually used for levelling interior floors. In a year or two or three any hack solution might crack, and you're screwed. Why should you have to deal with that? Jackhammer or bobcat it out and have him pour another one. Pouring a flat slab with a consistent slope for drainage should be easy for a real concrete guy. He will squeal like a stuck pig but the fact is, removing a hot tub sized slab is no big deal.

[AndyInSanCarloe]

I realize this is a couple of years old, but I’m curious how all of this works and have some additional questions.
 

My situation is I had an extensive concrete patio installed a few years ago. Naturally it’s full of rebar. Part of it is on a hillside and so I had them add a pad for a spa (it’s a Lifesmart LS600DX 220 volt self-contained unit). I think the shell is made out of polypropylene or some similar plastic. The concrete spa pad is down about 18” from the patio so it’s easy to step into the spa right onto the seat that is more or less level with the patio. This leaves the top of the spa about 18” above the patio. So that’s 10” less than the NEC code.

I asked the concrete guys to put a bonding wire in but they neglected to do so. The electrician put a box with a GFI breaker the requisite 6’ from the spa and that works fine. I believe the rebar for the patio and the pad is tied together but I’m not 100% sure. The spa pad is maybe 1” bigger than the spa itself.

So I’m trying to figure out what my exposure is and whether it’s worth it to rip out the spa slab to re-pour it with a proper bonding wire.

Just as a spot check I got out my handy voltmeter and checked the voltage difference between the spa water and the concrete patio where I poured some water into an expansion joint. It’s 0.05 volts.  I realize spot checking doesn’t account for all sorts of random and rare things that can happen far away to create a potential difference with the earth, but it gave me some comfort. We’ve used the spa on an occasional basis for 4 years or so and never had a shock of any kind. Again, I appreciate that any history is not a future guarantee.

So here is what I don’t get:

1) If the spa were 10” higher I believe it would be to code. I presume the thinking here is that nobody has 28” arms that can hang out of the spa and touch the concrete to close a circuit. But every time you go to check the chemicals or take of the lid you are standing on the concrete - often barefoot. Couldn’t you close the circuit there and get shocked? We don’t regularly sit with our arms hanging out on the patio, but getting in and out is usually one foot on the patio and one in the spa. I just don’t see it as all that different than putting your hand in the spa on an installation with 28” clearance that is to code. So it seems like they are a little worried about this but not a lot worried. Do other things have to go wrong for a self contained spa to become shocky?

2) Couldn’t I simply have an electrician put a grounding rod in the dirt right next to where the patio and the pad for the spa meet? Wouldn’t that bond the spa to earth right where the patio is bonded to earth and alleviate 99% of the potential for a voltage difference to build up?

3) I guess you can also put a loop of #8 wire in the dirt around the spa. The problem for me is the spa pad and the patio are integral so for that side of the spa the wire would not be buried 4-6” deep - it would be on top of the concrete. I also don’t fully understand the need for a loop. Isn’t the grounding rod basically equivalent?

I’m a bit *** about these sorts of things and it frustrates me not to be able to understand not just what the requirements are but also why. What is the scenario they are concerned about, how does it come about and what are the potential ways to mitigate - to what level of effectiveness?

Thanks all.

Andy

San Carlos, CA

 

[agster27]

I did a #8 wire around the perimeter. 

I am not an electrician just a nerd.  I will explain it in very simple terms.

Grounding - provides a path for say a short circuit to earth.

Bonding - connects to all equipment to ensure they are all equalized to avoid a discharge between objects.

They work together.

Different areas have different codes. I would highly recommend doing both.

Good luck!