Bonding to Plumbing

None taken. The NEC does not spell out where the water bond has to be, It only spells out that it has to be a water contact area of at least 9 square inches. I will agree that some systems that have bypass loops in place for heaters could circumvent the bond and that would have to be taken into consideration when designing the bond system.There are a few devices out on the market that are designed to be a water bond. One good one is mounted in the skimmer and sits tight against the wall. Another one replaces a hose connection at the pump or skimmer with a stainless steel fitting that can be bonded to. Resistance of the water is not realy an issue in this situation as the bond is meant to equalize potential difference by eliminating resistance between two different potentials. Without the bond in place you become the resistive path between the potentials and it can sometimes be painfull. Here is an incredible video of how voltage potential works. http://www.youtube.com/watch?v=LIjC7DjoVe8 At 1:38 in the video he somewhat explains how potential works.

Remember, in a grounding system, we are flowing current from the defect in the electrical system back to source. The ground wire acts as a low resistance path so you don't get shocked. In a bonding system we are simply keeping two or more voltage potentials equal. As long as the bond between these different potentials is of low enough resistance they will equal out and you don't become the conductor

Resistance = impedance for AC right?

Can pool water be bonded within the plumbing only? Luckily this is one of the few problems I've never experienced with my 40(?) year old pool.
 
In my area they used to let you do this.
A couple years ago we got a new inspector for the area and he no longer allows heaters to be the water bond. He will still allow a short section of brass or copper pipe in a suction or return line near the pool but, likes to see a waterbug in the skimmer or a light niche.
 
Resistance = resistance. Impedance is how A/C circuits react to resistance.

If you have a 40yo pool with copper piping your water bond could just be the pipe. Also if you have a light in your pool the metal light housing acts an acceptable bonding point for your water assuming the housing was connected to the bonding loop. For people with vinyl liners and plastic pipe and no metal ladders or lights special attention must be paid to add a dedicated water bond point. I doesn't hurt to have a dedicated water bond fitting for any pool but it isn't always needed as something may already be doing the job. As danpik said it just has to a min of 9 square inches of surface area of corrosion resistant metal in contact with the water connected to the bonding loop to meet the NEC code rules. They don't specify how or where it must be installed.

Counting on a heater to be your bonding point is troublesome as most heaters can be valved out and or removed from the piping thus eliminating your water bond.
 
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