Hot Tub Bonding

[Dennis Alwon]

We did a job recently where we had a hot tub set into a deck. I, of course, had them run the equipotential bonding in the dirt beneath the deck and around the tub as required.

The deck has wooden posts with metal piping running horizontally between the posts. You can actually turn the pipes thru the holes that were drilled. The NEC requires all metal parts within 5' of the tub to be bonded. Okay, so what value does it have to bond these rails.

If, theoretically, the deck has the equipotential bonding then the deck would have the same potential as the voltage in the earth (if there is any). So why would these pipes need to be bonded? They are going thru holes in the posts and any connection there should be the same as the deck. I am afraid by bonding the pipes then you may have a different potential between the rails and the deck.

We did not bond it but the inspector is requiring it. He is using the NEC appropriately however, I think it is a mistake. What do you think?

Btw, it is not that big of a deal to bond it, I just think it may do more harm than good.

 

[Knuckle Dragger]

Hi just trying to understand the delema.
Are you saying that the inspector wants the piping to be bonded separately from the equipotential bond system you set up or is that what the NEC says?

 

[Dennis Alwon]

The inspector wants the piping bonded per the nec- to the equipotential bonding. I feel that doing so may be more dangerous than not bonding it. These metal pipes are horizontal and the only contact with the earth is thru the holes bored in the posts.

Just trying to get feedback on that... We will bond it.

 

[Craigv]

We did a job recently where we had a hot tub set into a deck. I, of course, had them run the equipotential bonding in the dirt beneath the deck and around the tub as required.

The deck has wooden posts with metal piping running horizontally between the posts. You can actually turn the pipes thru the holes that were drilled. The NEC requires all metal parts within 5' of the tub to be bonded. Okay, so what value does it have to bond these rails.

If, theoretically, the deck has the equipotential bonding then the deck would have the same potential as the voltage in the earth (if there is any). So why would these pipes need to be bonded? They are going thru holes in the posts and any connection there should be the same as the deck. I am afraid by bonding the pipes then you may have a different potential between the rails and the deck.

We did not bond it but the inspector is requiring it. He is using the NEC appropriately however, I think it is a mistake. What do you think?

Btw, it is not that big of a deal to bond it, I just think it may do more harm than good.

I think it's an unknown as to whether the deck (even wet) would have the same potential as wet earth. And the deck would be an extremely high impedance connection to the earth. The pipes definitely will conduct with low impedance, so maintaining them at the same potential as other metallic parts is critical. There is nothing you can do to change the conductivity or impedance of the wooden deck components. At the very least, all of the interconnections where pipes run through wood, if the pipes are bonded, would help maintain the deck at a closer potential to the rest of the system.

There's also the issue, even if quite a remote possibility, that if the pipe came in contact with an energized conductor, if it was bonded it would at least have a shot at tripping an OCPD.

 

[Dennis Alwon]

I think it's an unknown as to whether the deck (even wet) would have the same potential as wet earth. And the deck would be an extremely high impedance connection to the earth. The pipes definitely will conduct with low impedance, so maintaining them at the same potential as other metallic parts is critical. There is nothing you can do to change the conductivity or impedance of the wooden deck components. At the very least, all of the interconnections where pipes run through wood, if the pipes are bonded, would help maintain the deck at a closer potential to the rest of the system.

So you are seeing it as the pipes bringing the wood to a voltage potential more in line with the earth. Hum, even with the pipes just laying in the holes that are drilled? Maybe, It seems like the pipe would be a different potential then the deck when you bond the pipe and that is what bothers me

 

[Craigv]

So you are seeing it as the pipes bringing the wood to a voltage potential more in line with the earth. Hum, even with the pipes just laying in the holes that are drilled? Maybe, It seems like the pipe would be a different potential then the deck when you bond the pipe and that is what bothers me

It (the deck) probably would be at a different potential, but it has such high impedance it's unlikely to matter from a human hazard standpoint. If its impedance was low enough to pose a threat, it would be able to maintain a closer potential to the pipes just by the minor physical contact.

 

[Craigv]

Just thinking, if you have the time and inclination, you could run a small experiment....before you connect the bonding to the rest of the system, energize one of the pipes, and read voltage from it to a spot on the deck within body length distance from it.

 

[ActionDave]

The inspector wants the piping bonded per the nec- to the equipotential bonding. I feel that doing so may be more dangerous than not bonding it. These metal pipes are horizontal and the only contact with the earth is thru the holes bored in the posts.

Just trying to get feedback on that... We will bond it.

I see it the way you do Dennis. It's kinda like having an two wire plug in a living room of a wood framed house, there is no way to get shocked from a ground fault till someone adds a circuit with an equipment ground.

 

[kwired]

I understand it isn't too likely to ever be a problem, but the idea is all conductive items within a certain zone are all at the same potential.

Someone drapes holiday lighting from those metal pipes (hopefully they are plugged into a GFCI protected outlet) but if pipes truly are isolated still shouldn't trip if a fault occurs to the pipe, but if pipes are bonded they stay at/near same potential as the pool/spa during this fault event.

 

[Dennis Alwon]

I understand it isn't too likely to ever be a problem, but the idea is all conductive items within a certain zone are all at the same potential.

That is my point. Will the wood posts and the bonded metal pipes be at the same potential? I don't think so, but maybe I am wrong.

Someone drapes holiday lighting from those metal pipes (hopefully they are plugged into a GFCI protected outlet) but if pipes truly are isolated still shouldn't trip if a fault occurs to the pipe, but if pipes are bonded they stay at/near same potential as the pool/spa during this fault event.

Yeah well someone can hang the lights on the edge of the tub also. All the outlets near the tub are gfci.

 

[kwired]

That is my point. Will the wood posts and the bonded metal pipes be at the same potential? I don't think so, but maybe I am wrong.



Yeah well someone can hang the lights on the edge of the tub also. All the outlets near the tub are gfci.

You are not going to raise the voltage of the wood posts much at all unless they are totally saturated. What concerns me more is if there would be voltage between the metal pipes and the pool/spa. Aren't all exposed fixed metal items within the "bonding zone" and over 4 inches in any dimension required to be bonded regardless of what they are in contact with?

 

[Mystic Pools]

We bond our rebar on our concrete pools and they are within the concrete when the shell is complete. What's different about bonding these pipes? They are just covered in a different material which will soak up moisture faster than concrete.

Make sense to anyone?

I would bond them.

 

[Craigv]

I think it should be recognized that the intent of equipotential bonding, as stated in 680.26 is, "...to reduce voltage gradients in the pool area." The key word here is "reduce". This wording accounts for the fact that it is impossible to eliminate voltage gradients.

I think we can mostly agree that it's impossible to raise a concrete pool deck, or an unpaved pool perimeter area to the same potential as, say, a metal ladder. Yet we install perimeter rings and tie rebar into the system. I don't think a wooden deck is any different. A gradient will exist...it has to...but the bonding will *reduce* it far more than if it were not bonded. The impedance of even a completely saturated treated wood deck board is extremely high, so I guess I don't see the danger in this situation.

 

[kwired]

I think it should be recognized that the intent of equipotential bonding, as stated in 680.26 is, "...to reduce voltage gradients in the pool area." The key word here is "reduce". This wording accounts for the fact that it is impossible to eliminate voltage gradients.

I think we can mostly agree that it's impossible to raise a concrete pool deck, or an unpaved pool perimeter area to the same potential as, say, a metal ladder. Yet we install perimeter rings and tie rebar into the system. I don't think a wooden deck is any different. A gradient will exist...it has to...but the bonding will *reduce* it far more than if it were not bonded. The impedance of even a completely saturated treated wood deck board is extremely high, so I guess I don't see the danger in this situation.

Here we have a conductive component and an insulating component - that is a capacitor. Bonding the metal pipes will eliminate capactively coupled voltage on those pipes as referenced to the pool/spa.

 

[Craigv]

Here we have a conductive component and an insulating component - that is a capacitor. Bonding the metal pipes will eliminate capactively coupled voltage on those pipes as referenced to the pool/spa.

So in effect, that bonding would act as a drain. Interesting take. This would only work if the bonding is effectively connected to the grounding electrode, or by some other low impedance earth connection.

 

[kwired]

So in effect, that bonding would act as a drain. Interesting take. This would only work if the bonding is effectively connected to the grounding electrode, or by some other low impedance earth connection.

To drain a capacitor all you need to do is short the two plates together. Permanently short them together and you don't have a capacitor anymore.

 

[Craigv]

To drain a capacitor all you need to do is short the two plates together. Permanently short them together and you don't have a capacitor anymore.

Exactly. But this construction creates a rather untidy capacitor so defining it and shorting it wouldn't be very predictable. Especially when the shorting means (the pipes) could also be the charging means.

 

[kwired]

Exactly. But this construction creates a rather untidy capacitor so defining it and shorting it wouldn't be very predictable. Especially when the shorting means (the pipes) could also be the charging means.

I guess my point all along is bonding turns what was a natural capacitor into a non capacitor. All metallic components will remain at same potential. They may change potential in relation to something not bonded. This is what equipotential bonding is all about though, everything bonded is at same potential.

 

[Craigv]

I guess my point all along is bonding turns what was a natural capacitor into a non capacitor. All metallic components will remain at same potential. They may change potential in relation to something not bonded. This is what equipotential bonding is all about though, everything bonded is at same potential.

Yes, it all should be at the same or very close potential. But you raised an interesting point...that the decking could in effect create a capacitor, which is a storage rather than conductive medium. Bonding the pipes would not necessarily drain the charge, and could actually work to charge the capacitor instead. It's all very undefinable and mostly theoretical. I'm no dirt worshipper by any means, but do think the pipes should be bonded in this instance.

 

[kwired]

Yes, it all should be at the same or very close potential. But you raised an interesting point...that the decking could in effect create a capacitor, which is a storage rather than conductive medium. Bonding the pipes would not necessarily drain the charge, and could actually work to charge the capacitor instead. It's all very undefinable and mostly theoretical. I'm no dirt worshipper by any means, but do think the pipes should be bonded in this instance.

Equipotential bonding isn't about draining the charge, and it isn't about additional "grounding/earthing" - it is about putting everything you do bond at the same potential.

Bonding those pipes to the tub just increases the size of the capacitor plate.

That said the tub is still supposed to get connected to an EGC nearly every case so that will end up draining the capacitor anyway.