2020 BURNDY Master Catalog

Reference

Introduction Basic Electrical Connections Principles

Introduction - Basic Electrical Connection Principles (continued)

Aluminum to Aluminum Connections: For joining aluminum to aluminum conductors, there is little disagreement that an aluminum bodied connector is the proper choice, since this obviously elimates the galvanic corrosion of dissimilar metals. However, even in this case, care must be taken to prevent crevice corrosion and to select an alloy of aluminum for the connector body that is free from cracking due to stress corrosion. Aluminum to Copper Connections: Similarly, for joining aluminum to copper conductors, an aluminum bodied connector is the best choice since it prevents galvanic corrosion of the aluminum conductor, the most vulnerable element to attack in the connection. Realizing this, BURNDY initiated a research program aimed at finding the best way to make an aluminum connector suitable for joining aluminum to copper conductors. This led to the evolution of the “Massive Anode Principle” of connector design for joining conductors of dissimilar metal. On the basis of this principle, properly designed, all-aluminum connectors became available for universal use in joining aluminum to aluminum or aluminum to copper conductors. Massive Anode Principle: By making the aluminum connector massive in comparison to the copper conductor, when the copper conductor emerges from the connector, the electrolytic current density over the exposed face of the aluminum connector is greatly reduced. This is schematically represented in Figure 4. Since the rate of corrosion is directly related to the current density on the surface of the anodic material, the relatively large face of the aluminum connector will suffer only minor attack.

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LESS NOBLE (ANODIC) Magnesium Magnesium alloys Zinc Aluminum 1100 Cadmium Aluminum 2024-T4 Steel or Iron Cast Iron Chromium Iron (Active) Ni-Resist Type 304 Stainless (Active) Type 316 Stainless (Active) Lead Tin Solders Lead Tin Nickel (Active) Inconel Brasses Copper Bronzes Copper-Nickel alloys Monel Silver Solder Nickel (Passive) Inconel (Passive) Chromium-Iron (Passive) Type 304 Stainless (Passive) Type 316 Stainless (Passive) Silver Titanium Graphite Gold Platinum MORE NOBLE (CATHODIC)

Figure 3

Corrosion Testing: The effectiveness of an electrical connection to resist corrosion can be tested in the laboratory under conditions designed to greatly accelerate the natural corrosive conditions of actual service. The most widely accepted means is the standard salt spray chamber. In this chamber the specimens are placed in a salt fog made by atomizing a 20% salt solution at 100˚ F. BURNDY, as well as other manufacturers and utility companies, have done a great deal of testing and a considerable area of agreement has been reached. There are, however, minor differences in recommended practices. The problem is concerned with aluminum and aluminum to copper connections since the effect of corrosion on copper to copper connections is far less serious. Let us study the recommended practices.

Figure 4

In addition, because the aluminum connector body is massive in the region where the corrosion occurs, the small loss of metal caused by corrosion is insignificant, even after long periods of service. Furthermore, the connector design should be such that clamping bolts, and areas of high stress which provide structural strength, are not in the regions subject to galvanic attack. The effectiveness of this theory has been amply demonstrated in salt spray corrosion tests in which the connectors were subject to 1,000 hours in the salt

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