Do you need a bonding grid around a hot tub?

[goldstar]

Phil, why woud the hazrad be any less on an existing situation.
If a equipotential grid is needed on a new install would it not be needed on a retrofit ?

Gus,

I don't believe there's any difference in hazard potential in either case. However, I think the code section needs to be revisited and here's my reasoning : What difference would it make if the EPBG were placed just under the edge of the tub and then bonded to the motor ? Would you truly get that much less benefit if the wire didn't fall within the 18"-24" perimeter of outside of the tub ? In the case of a concrete slab couldn't a ground rod or two be driven near the tub and bonded to instead of breaking up the entire slab ? Wouldn't you get the same benefit ? This section of the code only deals with new tub installations where disturbing soil or landscaping is not an issue. Quite frankly, all it does is increase the cost of the entire tub installation and in many cases discourages homeowners from even buying a tub. It also leads to the probability bootlegged work getting done by unscrupulous contractors or homeowners themselves. I'm not suggesting that the CMP's make this section of the code more lenient in all cases but they should realize that everything isn't always so cut and dry and some concessions could be made. There are a lot of smaller homes in my area that barely have a front lawn to speak of and in many cases their back yards are almost all patio. Compelling these homeowners to break up their patios or dig up whatever lawn they have I think is rather extreme.

Just my opinion.

 

[goldstar]

I did a quick test on my deck (no hot tub). It is 2x6 deck on 2x8 joists with brass screws holding the deck to the joists. It rained a bit about 24 hours ago, but today was warm and sunny.

I did not let the water really soak in before I ran the "wet test". The megger leads are connected to the brass screws.

Interesting Don. Please tell us what the readings indicate. Did you actually connect a power source to the boards or just meg out from one screw to another ?

 

[mivey]

What about hot tubs that are built with wood? :-?

They will require an inner mesh bowl made of galvanized chicken wire. Not too comfortable, be at least it will be safe.

 

[electricmanscott]

They will require an inner mesh bowl made of galvanized chicken wire. Not too comfortable, be at least it will be safe.

And of course the new lead bathing suit requirement. Safety first!

 

[wawireguy]

How is the water bonded in a hot tub? And what if the wood was treated with tompson's water seal, then the water would bead and wouldn't be a continous path. I got a lot of good laughs from this topic, and so good info too.

In self contained/portable type hot tubs, like Apollo and the like the heater is in a stainless tube that has a bonding jumper to the EGC you bring in. So that's how the water gets bonded.

 

[macmikeman]

I'm going to really mess up the way this thing has been going. Around here they mostly don't use wood decks for hot tubs, they use Trex... So now what do we do??

P.S. in case somebody isn't familiar with Trex, its a mix of plastic, resin and so forth molded into planks like wood, that you can sawcut and holds up much better in Hawaiian weather than wood does.

 

[electricmanscott]

I'm going to really mess up the way this thing has been going. Around here they mostly don't use wood decks for hot tubs, they use Trex... So now what do we do??

P.S. in case somebody isn't familiar with Trex, its a mix of plastic, resin and so forth molded into planks like wood, that you can sawcut and holds up much better in Hawaiian weather than wood does.

Tell us what you would do? If you would bond it HOW would you do it.

 

[don_resqcapt19]

Interesting Don. Please tell us what the readings indicate. Did you actually connect a power source to the boards or just meg out from one screw to another ?

It was just megged with the megger set at 100 volts. I also did one with the leads connected directly to the wet board and got 0.31 meg. That would give you 0.38 mA of current flow with a 120 volt supply. That it probably not enough current to cause any issues. I expect that if I would have let the water soak into the wood so there was a larger cross sectional area that was wet that the resistance would go down and we may get to the point where the would could carry enough current to trip a GFCI.
The dry wood at 3.65 meg would only flow 0.03mA...not sure if you could even feel that.

 

[M. D.]

Tell us what you would do? If you would bond it HOW would you do it.

Scott, once you bond all the screws ,..they will bond the wood ,...:grin:

 

[wasasparky]

Grounding Gone Wild?

Grounding Gone Wild?

I respectfully and strongly disagree, there is a real safety issue here that is the same for new or old installations.

For a packaged hot tub on a wood deck I struggle to agree that there is a real safety issue.

The important thing to me would be good bonding back to the source.

Why don't we require ground grids around all light poles to reduce touch potential?

 

[mivey]

For a packaged hot tub on a wood deck I struggle to agree that there is a real safety issue.

He was not referencing a wood deck. The wood deck bonding stuff has been kind of tongue-in-cheek.

 

[iwire]

For a packaged hot tub on a wood deck I struggle to agree that there is a real safety issue.

First I was specifically talking about grass and dirt installations not the wood deck issues.:smile:

The important thing to me would be good bonding back to the source.

Why don't we require ground grids around all light poles to reduce touch potential?

Second your are confusing the grounding back to the source with the equal potential bonding. It is extremely important that all parts around the pool are at the same (or as close as possible) to the same potential. This has nothing to do with the EGC back to the source.

He was not referencing a wood deck. The wood deck bonding stuff has been kind of tongue-in-cheek.

Thanks.:smile:

 

[wasasparky]

First I was specifically talking about grass and dirt installations not the wood deck issues.:smile:

Fair enough.
How about a packaged unit on grass/dirt?
Ground mesh code required - yes, but I fail to see the need.
Should I not assume the spa was built safely?
If the spa shorts, does the ground mesh save me?
(I'm just talking small cord-n-plug spas here - not pools...)

Second your are confusing the grounding back to the source with the equal potential bonding. It is extremely important that all parts around the pool are at the same (or as close as possible) to the same potential. This has nothing to do with the EGC back to the source.:

I'm not confusing anything, maybe just not phrasing things properly.

 

[don_resqcapt19]

Fair enough.
How about a packaged unit on grass/dirt?
Ground mesh code required - yes, but I fail to see the need.
Should I not assume the spa was built safely?
If the spa shorts, does the ground mesh save me?
(I'm just talking small cord-n-plug spas here - not pools...)

Since we have bonded and energized the conductive parts of the hot tub and its water, we must also energize the area around it to make it safe to enter and exit the water.

 

[wasasparky]

Since we have bonded and energized the conductive parts of the hot tub and its water, we must also energize the area around it to make it safe to enter and exit the water.

As my 2-year-old would say... Why?

Once again, my point being for the small cord/plug connected portable spa's...

 

[wwhitney]

How about a packaged unit on grass/dirt?
Ground mesh code required - yes, but I fail to see the need.

OK, let me take a stab at trying to explain, hopefully someone will correct me if I say anything wrong.

The water in the spa is likely to be bonded via the EGC in the branch circuit serving the spa, even if it is not intentionally done. Since the EGC is earthed at the service main disconnect, the water in the spa is now at the potential of the earth near the main disconnect.

However, the earth near the spa may be at a different potential, because the electrial distribution system uses a multi-grounded neutral, so the earth is in parallel with the distribution neutral, and some current flows through the earth. This potential difference between the spa water and the earth around the spa results in a shock hazard.

Cheers, Wayne

 

[zappy]

Talked to a inspector today, and he said if its a wood deck, then it's not required.

 

[electricmanscott]

Talked to a inspector today, and he said if its a wood deck, then it's not required.

Yes! The good guys win! :grin:

 

[hurk27]

If the spa shorts, does the ground mesh save me?

This is not the purpose of a equal potential bonding grid, if there is a short on the electrical system the EGC ran with the circuit conductors will open the breaker, or GFCI device.

The equal potential bonding grid, only connects all points of the tub and the surrounding area together to bring it to the same potential (voltage), this is the same as why a bird can sit on a wire with high voltage on it, if all points are connected together a person can't contact two points with a difference of potential (again voltage) and current can't flow.

This is why the EPBG is not required to run back to the service panel, and can even be isolated from it in the case of a double insulate pump motor if that is the only electrical equipment the pools has. any fault current should only flow back on the EGC's or line to neutral where it should open a breaker or GFCI device.

I don't have the 2008 NEC yet, but has 680.43 been changed also or does it also state

A spa or hot tub installed indoors shall comply with the provisions of Parts I and II of this article

which would mean the wood floor indoors would have to be bonded?:-?

 

[Meremac]

Mother Earth

Mother Earth

Neither Lowes nor Home Depot has waterproof plywood with a bonding lug .....

It seems that the deck/floor situation involves seeing if the wet provides a path to ground that could threaten a user. Wood on the ground would provide a dandy ground path. A free draining wood deck would not unless it had some iron support beams or trusses or unless the draining surface water could pool against, as an example, an aluminum flashing over a ledger board which was in contact with 20 feet of concrete foundation. In these cases bonding the path to ground (the iron or the flashing) would seem to solve the problem.

As for the tub on the ground, it would seem that a copper ring could be "cut in" with a flat spade much as LoVo yard lites or sprinklers are often installed. The garden folks seem to get on with stout long handled spades and lots of coffee. I don't know if that method would get enough depth or if the conductor could be adequately secured in place.

The floor thing still has me worried. During the remodel I had galvanized framing ell metal put all along the floor-wall joint under the concrete backer board to get a water resistant tub floor. The metal isn't bonded so I guess I better watch out for thunder things when I'm on the pot.