Pool cage bonding

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texie

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Fort Collins, Colorado
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Electrician, Contractor, Inspector
Coyote said:
What is the best way to bond a pool cage,considering the aluminum frame copper lug bolts and moisture? :?
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I spent a good part of my career in an area that every other house had a pool. Oh wait, every house in some areas. Been a while though, but AHJs accepted (back then) just a ALCU lug attached with a tek screw. I always preferred a lug bolted through an enclosure framing member using a stainless steel bolt and nut. I used see to many where the tek screw would fall out from corrosion after time due to the ferrous tek screw reacting with the aluminum structure.
"pool cage" sounds like a SW Florida term.:)
 
Coyote

Coyote

Member
Location
Illinois
texie said:
I spent a good part of my career in an area that every other house had a pool. Oh wait, every house in some areas. Been a while though, but AHJs accepted (back then) just a ALCU lug attached with a tek screw. I always preferred a lug bolted through an enclosure framing member using a stainless steel bolt and nut. I used see to many where the tek screw would fall out from corrosion after time due to the ferrous tek screw reacting with the aluminum structure.
"pool cage" sounds like a SW Florida term.:)
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Yes SW Florida it is our retirement home, were there any corrosion issues with the stainless screws and the frame of the cage?
 
tom baker

tom baker

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Location
Bremerton, Washington
No. You want metals that are close together on the corrosion scale, which AL and SS are. Keep in mind there is 304 SS and 316SS, the 316 is more corrosion resistant. The Solar industry has worked thru these issues and they have good solutions.
 
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suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
I agree you want metals close together on the corrosion scale, but SS and Al are rather far apart. Zinc, cadmium, and mild steel are closer to aluminum than stainless steel (with 410 and 416 SS being closest). The SS is more cathodic which says to me the aluminum structure (if threaded) will corrode first and the stainless steel fastener will pull out but be mostly pristine. Best to avoid threading the aluminum and use a normal bolt and nut.

I would think you'd be better off with a cadmium plated steel bolt or perhaps even a galvanized bolt, as the zinc will go first (more anodic than aluminum). Aluminum and steel and cadmium are next to each other on the galvanic scale. Zinc is next to aluminum the other direction. An SS screw would probably be OK if you drill a hole in the aluminum and not thread the aluminum. An aluminum screw and nut with an ALCU lug may be best, but just be careful not to strip the aluminum screw and nut (not sure if there are aluminum lock washers though).

Covering the assembly with a weatherproof sealant after it is made up and the wire attached may also help things. A zinc based anti-sieze on the bolt may also be a good idea. You want to keep the water out, and pool water is nasty because of the occasional high levels of chlorine. I had a pool cover that used an aluminum tube with stainless spring latches to the pole sections together. After a year in the pool, the aluminum was quite white and eaten where those SS springs touched holes in the aluminum tube.
 
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