Hot tub Question

[olly]

I am hooking up a used hot tub, I've got an existing whip with the two hots, nuetral, and ground in a SO sheath. Then there is a #6 bare CU wrapped around it? Is this Bare CU used for a ufer ground? Is that mandatory? I will be setting this tub on an existing pad with no way to get to the rebar... Can I just discard this bare ground?

 

[Dennis Alwon]

That may have been the equipotential bonding wire but I don't know. Usually that wire is connected to the pump lug and then run around the perimeter of the tub. You may or may not need the #6-- read below esp. #4

(B) Bonding. Bonding by metal-to-metal mounting on a
common frame or base shall be permitted. The metal bands
or hoops used to secure wooden staves shall not be required
to be bonded as required in 680.26.
Equipotential bonding of perimeter surfaces in accordance
with 680.26(B)(2) shall not be required to be provided
for spas and hot tubs where all of the following
conditions apply:
(1) The spa or hot tub shall be listed as a self-contained spa
for aboveground use.
(2) The spa or hot tub shall not be identified as suitable
only for indoor use.
(3) The installation shall be in accordance with the manufacturer’s
instructions and shall be located on or above
grade.
(4) The top rim of the spa or hot tub shall be at least
710 mm (28 in.) above all perimeter surfaces that are
within 760 mm (30 in.), measured horizontally from
the spa or hot tub. The height of nonconductive external
steps for entry to or exit from the self-contained spa
shall not be used to reduce or increase this rim height
measurement.

 

[FionaZuppa]

where does the #6 go? is it attached to anything?
most likely is bonding wire.

 

[kwired]

where does the #6 go? is it attached to anything?
most likely is bonding wire.

OP has a used unit and this conductor is part of what was connected to it before. He may or may not need this conductor in his new location. It also likely only needed to be 8 AWG whatever it went to.

 

[FionaZuppa]

OP has a used unit and this conductor is part of what was connected to it before. He may or may not need this conductor in his new location. It also likely only needed to be 8 AWG whatever it went to.

yes, it connects to somewhere to the spa, where is it attached to the spa? likely a bonding lug there.

 

[kwired]

yes, it connects to somewhere to the spa, where is it attached to the spa? likely a bonding lug there.

Of course it attaches to the spa, likely to the lug typically located right on the exterior of the pump motor, the point I was getting at is in some cases the "other end" doesn't need to connect to anything. This lug is for bonding to other items in the vicinity of the spa for equipotential reasons, if you have nothing in the vicinity to bond to you don't have to use it for anything. You still must have an equipment grounding conductor with the supply conductors, which OP says is already in the "supply whip".

All that tells me is wherever the thing was connected before must have had other items in the vicinity that needed bonded to the spa, or someone didn't know what that lug was for and connected it to something they maybe didn't necessarily need to, like a ground rod?

 

[FionaZuppa]

All that tells me is wherever the thing was connected before must have had other items in the vicinity that needed bonded to the spa, or someone didn't know what that lug was for and connected it to something they maybe needed to, like a ground rod?

a ground rod is a great idea

 

[kwired]

a ground rod is a great idea

Can be a horrible idea depending on conditions and how it is done. Equipotential grid in a slab that the spa sits on is a much better thing to have.

 

[FionaZuppa]

Can be a horrible idea depending on conditions and how it is done. Equipotential grid in a slab that the spa sits on is a much better thing to have.

yeah, well, my spa sits on a plastic pan, on the dirt. what slab ?

how much $$ you have to bet with. a 7'x7' 3" thick slab with wire mesh (typical for a decent size hot tub), vs my 20ft ground rod. you willing to bet the slab has less ohms back to panel than the rod ??

 

[kwired]

yeah, well, my spa sits on a plastic pan, on the dirt. what slab ?

how much $$ you have to bet with. a 7'x7' 3" thick slab with wire mesh (typical for a decent size hot tub), vs my 20ft ground rod. you willing to bet the slab has less ohms back to panel than the rod ??

I could care less if there were any continuity back to the panel, the reason we put in equipotential bonding is so the user doesn't touch two points of different potential, we want the slab and the hot tub to not have any voltage between them when we step out. They can both be 5000 volts above the potential at the panel, but we are not touching the panel at the same time as we are touching the hot tub or the slab so we really don't care what potential is to the panel.

We do want a low impedance path to the source to facilitate overcurrent protection clearing ground faults, but that path may still have some potential to "earth ground" caused by voltage drop on grounded service conductor.

 

[FionaZuppa]

I could care less if there were any continuity back to the panel, the reason we put in equipotential bonding is so the user doesn't touch two points of different potential, we want the slab and the hot tub to not have any voltage between them when we step out. They can both be 5000 volts above the potential at the panel, but we are not touching the panel at the same time as we are touching the hot tub or the slab so we really don't care what potential is to the panel.

1) ok, lets say you have a 9x9 on-grade slab with mesh, a 7x7 spa sits centered on that, you bond motor lug to mesh. the egc from sub panel has corroded and is now a 150k resistor. the bond becomes 240vac for whatever reason, you step out wet and one foot is on earth one foot is on slab.

2) take the same scenario but jab earth with a 20ft ground rod right next to slab, buried, attach bond grid to rod.

you would choose option 1 over option 2?

within NEC 680, the notion of equi bonding does not exist unless the EGC is lost. since 680 requires pool pump to have EGC connection (with most everything else within the pool/spa wiring has the egc tied to everything else that is metal), after applying the rest of 680 what you are left with is a everything that is grounded. a big system of connected EGC's that have no tie back to the supply grounded (earth) conductor is nothing more than a ungrounded equi bonded grid, like standing bare foot on a 10x10 wire mesh in the dirt. a ungrounded equi grid can still pose a hazard :thumbsup:

but look at the metal pool ladder, typically is not tied to EGC, so you bond it to the "equi grid", which is directly tied to the EGC elsewhere, thus ladder is now grounded.

the ground rod has a purpose, it provides extra safety. seems to be optional within NEC books.

 

[kwired]

1) ok, lets say you have a 9x9 on-grade slab with mesh, a 7x7 spa sits centered on that, you bond motor lug to mesh. the egc from sub panel has corroded and is now a 150k resistor. the bond becomes 240vac for whatever reason, you step out wet and one foot is on earth one foot is on slab.

2) take the same scenario but jab earth with a 20ft ground rod right next to slab, buried, attach bond grid to rod.

you would choose option 1 over option 2?

within NEC 680, the notion of equi bonding does not exist unless the EGC is lost. since 680 requires pool pump to have EGC connection (with most everything else within the pool/spa wiring has the egc tied to everything else that is metal), after applying the rest of 680 what you are left with is a everything that is grounded. a big system of connected EGC's that have no tie back to the supply grounded (earth) conductor is nothing more than a ungrounded equi bonded grid, like standing bare foot on a 10x10 wire mesh in the dirt. a ungrounded equi grid can still pose a hazard :thumbsup:

but look at the metal pool ladder, typically is not tied to EGC, so you bond it to the "equi grid", which is directly tied to the EGC elsewhere, thus ladder is now grounded.

the ground rod has a purpose, it provides extra safety. seems to be optional within NEC books.

equipotential bonding and equipment grounding are two separate functions. EB makes all items bonded together the same potential. EG gives you a low impedance path to the source to allow high level of current to flow during ground faults - which the higher the current the faster the overcurent protection device reaches instantaneous trip point and opens the circuit.

The thing with the EGC is it eventually ties to the grounded service conductor. The more current the grounded service conductor is carrying the more voltage drop will be on it and everything connected to it. If you have 3 volts drop on the GSC you have 3 volts to earth on everything in the pool because it is all tied to that GSC. But because it is all tied together you don't have any voltage between objects in the pool either.

Now in the case of the 7x7 hot tub on a 9x9 slab with bonding in the slab - there is going to be voltage gradient as soon as you step away from the slab, if the slab is at a voltage above earth. If you drive a rod, there will be a voltage gradient around that rod. Wet bare feet you probably feel some shock with either one if the voltage is much more then 3-5 volts, but won't be subject to any voltage if standing on the slab or even getting out of the tub and onto the slab, if the slab is well bonded.

Lose the EGC and your hot tub gets a fault in the pump? As long as you are in/on areas within the equipotential bonding zone you can easily be 120 volts above ground, only time you are at risk of shock is when you step away from any border of the bonding zone. If you create an equipotential plane that ramps deeper into the soil as you leave the slab your risk of shock while walking away decreases as that plane gets deeper.

Connect a ground rod to faulted equipment with no EGC, and there is voltage zones around that rod. You get one foot in one voltage zone and the other foot in another zone you have voltage between your feet, and will have current between them if not wearing well insulated footwear.

Bottom line put the ground rods at the service (if you don't have CEE's or building steel) and forget about them at the pool/hot tub, you won't get any benefit from putting them there, unless maybe you want to drive a huge network of them close to one another.