Hot tub Equipotential bonding of old concrete.


Old 09-05-19, 07:53 AM
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Hot tub Equipotential bonding of old concrete.

Hello everyone. I have an old 9x9 concrete pad with rebar and wire. Im going to put a hot tube on it however Im wondering if it would be ok to drill at 4 corners put a metal rod and attach it to the bonding solid copper wire. Would this bond the metal parts in the concrete?
I've read that concrete is very conductive so it would make since that attaching a rod to the concrete would bond everything that Is in contact with the concrete. Unfortunately because this is an old slab there is no rebar that is exposed for me to attach directly.

Thank you
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Old 09-06-19, 03:48 PM
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any body any ideas what I can do
Old 09-06-19, 04:04 PM
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Welcome to the forums.

Unfortunately Equipotential bonding is like voodoo magic. It is explained in the code but is a gray area and hard to decipher. It seems from what I've run into that it is almost completely up to the AHJ (inspector) what he wants and requires. I've had to bury a solid copper wire around a hot tub and connect it to the electrical ground. I've installed spas on a poured concrete pad and there was no concern over equipotential bonding.

I don't think concrete is considered a conductor. My pool has a 4' poured concrete sidewalk all the away around it with no bonding. The pool is concrete and has a fully bonded metal frame.

Here's where the concern is. If you can touch the water and the ground..... like earth..... you need a equipotential bond. This would require a copper wire to be buried just beyond the concrete.... in the dirt. The dirt is true ground. The hot tub connected thru the electrical wiring to the house panel is also "at ground" however the ground coming from the electrical service is not truly ground. There could be several volts between that and the actual ground. By connecting the hot tub ground to the earth ground you are ensuring that they are both at the same potential.....equipotential.

By drilling four holes in your concrete pad..... are you hoping the rods you put in will touch the steel in the concrete ? I wouldn't count on that.

If this is a permanent set-up..... apply for a permit and get it inspected.

Another one of the pro's may have more to add.
James168 voted this post useful.

Last edited by PJmax; 09-06-19 at 04:28 PM.
Old 09-06-19, 05:10 PM
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Thanks for the reply. I talked to my towns inspectors he said that if the hot tubes top rim is no less than 28” from ground level then there is no need for bonding. However the hot tub manual states to to bond all metal surfaces for the tub (pump etc...) so I think I’ll run a copper wire around the concrete pad and attach to all the metal parts the tub manual calls for.
concrete on its own is not conductive however because it’s lotus of it gets wet it becomes very conductive. The concrete pad is 9 by 9’. I was thinking that on the side where the steps are I could cut a grove full length an inch in depth till I hit rebar. In this gap barry 6ga copper wire and then fill the gap with concrete resurface. I think This wire would bond that whole area if saturated by water. What you guys think???
i overthink everything but just trying to be safe.
one thing I don’t understand is, Equipotential bonding equalizes differences between metal
surfaces, so that differences in volts won’t travel between A-B points. Are this differences in volts small volts which are not dangerous.?? As supposed to a bad gfci where you would get a high voltage shock.

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