disimilar metals

[Charles Bono]

Did an inspection of new home recently and found that the ground clamp attached to the incomming copper water supply pipe is made of metal and knowing that disimilar metals corrode over time, is it required to be called out?

I have called this out in other homes but it seems that all/most electricians use them. Surely they would know that disimilar metals corrode.


Thanks for the help.
Charles

[Bob Elliott]

Good point tho I would think that is not as serious as two supply line pipes having disimilar metals.
After all it is a lovely shade of green

[rwand1]

Personally I would not make an issue of it. I see white type metal clamps all the time on copper incoming water lines. Can't say as I have ever seen one causing a problem and I have been inspecting since 1991!

[Charles Bono]

Ray
thanks for your advice.

Charles

[rwand1]

as an additional note, in newer construction where the cold water line is bonded to the steel gas pipe leading at hot water heater all those clamps are the white metal variety, for what its worth.

[rwand1]

http://www.arrisistore.com/subcat.php?cat=NGD

[jkogel]

I'll bet there's a non-corrosive plating of some kind on those clamps, or an alloy rather than plain mild steel.
I'm posting a picture of a brass clamp on a galvanized steel ground rod with a rather tarnished copper grounding conductor, installed around 1965. I called for a repair here, but the worst corrosion is where the conductor is in contact with the dirt.

[rwand1]

On the link above it said some clamps are zinc or zinc coated?

[jkogel]

Originally Posted by rwand1

On the link above it said some clamps are zinc or zinc coated?

That is an interesting point, Raymond. On an outboard or a boat hull, the sacrificial Zinc is bolted to the leg or the hull because with electrolysis, especially in salt water, it corrodes faster than any of the other metal components. So the clamp will rust before the coper pipe.

[Yuri Olhovsky]

Corrosion can impede the quality of the ground. I don't make an issue out of it but I always recommend my clients to replace it. This is the same thing as copper hangers or copper nails used to support the copper pipe. If the pipe will be supported with galvanized hangers, I think everybody will call it out. Builders know that corrosion will occur there but it will take years. Bottom line is they can put clamp for about half price ($2 versus $4) and save some money </IMG>

[phinsperger]

The Galvanic Table

Active (Anodic) (+)

1. Magnesium
2. Mg Alloy AZ-31B
3. Mg alloy HK-31A
4. Zinc (hot-dip, die cast, or plated)
5. Beryllium (hot pressed)
6. Al 7072 clad on 7075
7. Al 2014-T3
8. Al 1160-H14
9. Al 7079-T6
10. Cadmium (plated)
11. Uranium
12. Al 218 (die cast)
13. Al 5052-0
14. Al 5052-H12
15. Al 5456-0, H353
16. Al 5052-H32
17. Al 1100-0
18. Al 3003-H25
19. Al 6061-T6
20. Al A360 (die cast)
21. Al 7075-T6
22. Al 6061-0
23. Indium
24. Al 2014-0
25. Al 2024-T4
26. Al 5052-H16
27. Tin (plated)
28. Stainless steel 430 (active)
29. Lead
30. Steel 1010
31. Iron (cast)
32. Stainless steel 410 (active)
33. Copper (plated, cast, or wrought)
34. Nickel (plated)
35. Chromium (Plated)
36. Tantalum
37. AM350 (active)
38. Stainless steel 310 (active)
39. Stainless steel 301 (active)
40. Stainless steel 304 (active)
41. Stainless steel 430 (active)
42. Stainless steel 410 (active)
43. Stainless steel 17-7PH (active)
44. Tungsten
45. Niobium (columbium) 1% Zr
46. Brass, Yellow, 268
47. Uranium 8% Mo
48. Brass, Naval, 464
49. Yellow Brass
50. Muntz Metal 280
51. Brass (plated)
52. Nickel-silver (18% Ni)
53. Stainless steel 316L (active)
54. Bronze 220
55. Copper 110
56. Red Brass
57. Stainless steel 347 (active)
58. Molybdenum, Commercial pure
59. Copper-nickel 715
60. Admiralty brass
61. Stainless steel 202 (active)
62. Bronze, Phosphor 534 (B-1)
63. Monel 400
64. Stainless steel 201 (active)
65. Carpenter 20 (active)
66. Stainless steel 321 (active)
67. Stainless steel 316 (active)
68. Stainless steel 309 (active)
69. Stainless steel 17-7PH (passive)
70. Silicone Bronze 655
71. Stainless steel 304 (passive)
72. Stainless steel 301 (passive)
73. Stainless steel 321 (passive)
74. Stainless steel 201 (passive)
75. Stainless steel 286 (passive)
76. Stainless steel 316L (passive)
77. AM355 (active)
78. Stainless steel 202 (passive)
79. Carpenter 20 (passive)
80. AM355 (passive)
81. A286 (passive)
82. Titanium 5A1, 2.5 Sn
83. Titanium 13V, 11Cr, 3Al (annealed)
84. Titanium 6Al, 4V (solution treated and aged)
85. Titanium 6Al, 4V (anneal)
86. Titanium 8Mn
87. Titanium 13V, 11Cr 3Al (solution heat treated and aged)
88. Titanium 75A
89. AM350 (passive)
90. Silver
91. Gold
92. Graphite

End - Noble (Less Active, Cathodic) (-)

[rwand1]

Fwiw

I have seen more lose clamps on the pipe and loose set screws on grounding clamps and bonding clamps. To me that is more of an immediate concern. Usually I just tighten the clamp.

[rwand1]

Copper is a Noble metal.
http://en.wikipedia.org/wiki/Noble_metal