I have an old in-ground pool with approx. 5 VAC between the water and ladder. I need to bond the ladder with the aluminum pool rim, as well as the pump and heater. The pool has a liner, and bonding to rebar is unlikely. I want to do the best I can without a backhoe.
The rim is in over 30 pieces, with readings of 0-5V. I can get aluminum 8-32 machine screws, but I want to know if there's any chemical reaction between stainless steel and aluminum. I'd like the completed setup to resist corrosion. I could also use a good suggestion for a lug to connect the 8 ga. solid to the rim.
Tiger, if I didn't know you, I'd say just unplug everything- permanently.
Aluminum and stainless make a very poor combination for screw threads; there are severe galling/' thread seizing problems. Even stainless-to-stainless can be a problem; best bet is to assume the pool parts are 300-series stainless, and use screws that are 400-series stainless. Other fastener materials that ought to work well with stainless, and much better with aluminum, are naval bronze, silicon bronze, and monel. Monel is a brass alloy that has the appearance and mechanical properties of stainless steel- it even looks silvery! When I need specialty fasteners, McMaster-Carr is on my short list. Great selection, great service- and not cheap!
Coating the threads with noalox, penetrox, or some similar stuff will reduce seizing, corrosion- and help maintain a good ground. Ditto for the contact face of the lug.
Assuming for the moment that the rim is of rather thin material, you might want to attach your lug to a stouter plate, then attach the plate to the rim with many small screws. In that scenario, you could even have the lug welded/brased to the plate!
Electrolytic corrosion between different metals, (or even the 'same' metal, but with different hardening qualities or alloy specifications), can be a bigger problem than galling, especially in a wet and chemically laden (chlorine) environment like a pool. I would suggest finding someone who can Tig/Mig or gas-weld aluminium, and bonding all the 30+ rim parts with aluminum wire or strip loops in inconspicuous positions, and using the same technique to provide a thicker Al. lug for grounding. Properly done, Al. welds will very neat, the expertise required is in welding the sheet metal without blowing holes in it! At the lug, protecting the interface (with a copper wire?) from corrosion can be effected with grease/sealant/paint to keep it dry. Alan
[This message has been edited by Alan Belson (edited 07-19-2005).]
I agree with getting a TIG welder to bond all of the segments together and then weld on a bond plate. You could then use a tin coated copper crimp connector (Burndy, T&B Color keyed) to connect the copper to the stainless. We have been using this method with great success. The first thing to go will be the copper, so protect it with a layer of paint or sealant until it is covered with insulation or gets out of continous contact with the water. We use 1/4-20 316SS or 304SS bolts with copper anti-sieze on the threads and can then easily remove them down the line if needed. Aluminum will likely melt away nefore your eyes... Aluminum is one step above zinc on the galvanic series...
Thanks for the help. I actually used to be a welder. Welding is a great solution, but this would be a tough one. The aluminum is all painted. The rim is backed and flush with concrete (if that makes sense to you).
The owner would like me to rewire the power to the pool pump house, but not do the bonding. They called the pool installer and building department and were assured that it was properly bonded when installed (this isn't a recent installation). I tried to explain that a properly bonded pool wouldn't give varying voltage readings between the ladders and different parts of the rim.
I also have a situation of neutral/ground bonding I posted in the code section I could use help with. I don't know if it's related to the pool situation or not.
I have this nagging feeling that this is a POCO problem. With the power off in the pool house sub-panel, the 100-amp sub-panel feeding that panel, and the power off in the 200-amp main panel feeding that...I still have a voltage reading at the pool. The only time I get no voltage difference at the pool (rim or ladder to water) is when I remove the neutral that feeds the pump house sub-panel.
Is it possible that this dry weather has made ground rods around the county ineffective?
Tiger I applaud your efforts and your tought to look at the grounding. You could rent a test instrument that will measure the resistance of the ground rod to the earth. It should be 5 ohms or less. If the resistance is higher than that additional sections of rod should be driven deeper to get the rod into a mineral layer with a higher dielectric constant (more conductive). You assesment though possible is rare, with the power connections open there should be no potential on the neutral unless the POCO isn't properly grounded.
With all of the power disconnected can you measure current on the neutral if you ground it to the pool?
[This message has been edited by Ray97502 (edited 07-20-2005).]
Thanks guys. The latest is the homeowner wants me to rewire the pool house, but not do the bonding. According to the pool installer and the building department, it was already properly bonded (whenever it was installed...not recently). I tried explaining that if it were bonded I wouldn't get different voltage readings at different points on the rim.