680 & Tubs

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
First, I have to say I'm not the EC on this job. (My only licenses are to drive a motor vehicle and run my amateur radio.) I design/spec/build/install various gadgets and deploy others. {Energy Detective, Ubiquiti, pond controls, etc.} My client/friend expects me to speak up when something concerts me. He's almost never afraid to exceed the minimum requirements. (He built his own 4000ft^2 log cabin near here; it has a septic tank sized for a 12 BR mansion.)

He's having a 17' Endless Pool/spa installed in a home solarium. I'm unsure/concerned about parts of the installation. The EC does not seem to think there are any issues. I've read 680 several times, watched Mike Holt's video, read other articles, and thus far, increased my ignorance....

It's in a foundation with a poured floor under it, and then a level just below the top. (Picture a shoebox with an oval hole in the lid.)

There is an insanely complicated and expensive sliding floor that covers the spa top while empty, and then when retracted, it forms the step down from the house. There's a ~8" block wall on the open side, and wood decking where the sliding floor ends.

A steel framework will go in to hold up the glass including patio doors. The glass is defogged al-la aircraft windshields; i.e. flashed with a metallic film that is a resistive heater. (The glass makes the floor look inexpensive.)

My first question is the tutorials differentiate between the equalpotential grid and grounding. Does that imply the grid shall not tied to the ECG?

I think the equalpotential grid rule does not apply here, but nevertheless I want to keep everyone safe. (I will likely get to use it, so....) To that end, I want to tie the poolwater (via a Perma-Cast PB2008 Water Bonding Fitting...) to the grid.

I also wonder about the distance between the floor's hydraulic pump motor and the spa.

Should I be looking at the rebar in the pour and adding it to the grid? The windows' steel grid?

I don't deny my ignorance here; feel free to delineate same.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
I don't know which statement you want spoken to but I will start with saying the grid is not required to go back to the panel. You can do it, but not required. The EGC of the equipment will, by default, tie it back via the bonding jumper from the equipment. As to the rebar, IMO, since this appears to be mostly field constructed, wouldn't qualify as a "self contained" unit and would require the equipotential bonding requirements from 680.
I'll just start here and let others add, and or correct, what I have said.
 

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
So here's a question that's come up. The solarium has common walls with the house. The GC plans to use Hardie Board siding for those walls for water resistance. But given cement is labeled a conductor, how does one connect it to the equilpotential grid? I'm pondering putting some metal mesh behind in, and grounding that.

I'm also thinking that since the sliding floor is part of the grid, and you step through the sliding door onto it, we should include that door as well.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
So here's a question that's come up. The solarium has common walls with the house. The GC plans to use Hardie Board siding for those walls for water resistance. But given cement is labeled a conductor, how does one connect it to the equilpotential grid? I'm pondering putting some metal mesh behind in, and grounding that.

I'm also thinking that since the sliding floor is part of the grid, and you step through the sliding door onto it, we should include that door as well.
Where does it say that Hardie board is a conductor? 110.26 mentions "Concrete, brick, or tile walls shall be considered as grounded" but that's about it.
 
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