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most vulnerable element to attack in the con-
nection. 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 Principal” of connector design for
joining conductors of dissimilar metal. On the
basis of this principal, properly designed, all-
aluminum connectors became available for
universal use in joining aluminum to alu-
minum 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 direct-
ly 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.
In addition, because the aluminum connector
body is massive in the region where the cor-
rosion occurs, the small loss of metal caused
by corrosion is insignificant, even after long
periods of service. Furthermore, the connec-
tor 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 spray fog with only
minor corrosive pitting adjacent to the copper
conductor, as seen in Figure 5. In addition,
the aluminum conductor was completely
protected, and the joint resistance remained
virtually unchanged. The test involved a wide
variety of sizes and types of connectors
showing the effectiveness for small service
connectors as well as large power connec-
tors. Figure 6 shows a large all aluminum
clamp type T connector installed on 3
1
2
diameter copper run and 750 kcmil aluminum
tap. The figure shows this connector opened
up after the 1,400 hours of the salt spray test.
Note that the contact surfaces are bright and
clean and the only evidence is minor pitting
along the faces adjacent to the copper.
*It should be emphasized that a good
compound should be used on the contact
surfaces whether aluminum or copper is
used in an aluminum connector.
Position of Conductor:
A properly designed
aluminum connector for joining aluminum to
copper must provide adequate separation
between the conductors to prevent electro-
lytic attack on the aluminum conductor. Even
then, it is good practice to install the
aluminum conductor above the copper con-
ductor if possible. This will prevent pitting of
the aluminum conductor due to copper salts
being washed over the aluminum.
Plated Aluminum Connectors:
Plating has
been used as a means to make an aluminum
connector suitable for copper conductor.
Such platings as copper, zinc, tin and cad-
mium have been used. The plating of
aluminum is much more critical than plating a
more noble metal such as copper. In addition,
a preplate, usually of copper or brass, must
be applied, thus introducing numerous
metals and further possibilities for galvanic
corrosion.
To be effective in reducing galvanic corrosion
between the copper conductor and the
aluminum connector, the plated metal must
be closer in the Electrolytic Series to copper
than is aluminum. It must therefore, be
cathodic to aluminum. Since porosity and
minor scratches are always present, galvanic
action can be expected in the presence of
moisture, resulting in attack of the aluminum
under the plating. Corrosion tests reveal
attack in the form of a mottled appearance
and flaking of the plating.
In addition, the presence of plated metal can
cause galvanic attack of the aluminum con-
ductor, thus reducing the protection offered
to this conductor in an aluminum connector.
Cleaning and the Use of Compound:
It
should be emphasized that when aluminum
connectors or conductors are involved,
proper cleaning of the aluminum and the use
of a good connector compound, such as
BURNDY
®
PENETROX A, are essential for
trouble-free service. BURNDY
®
, as well as
other manufacturers, provide the contact
grooves with a coating to make it unneces-
sary to clean the connectors, but in all cases,
INTRODUCTION
(Continued)
Fig. 3
Fig. 4
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
Nickle (Active)
Inconel
Brasses
Copper
Bronzes
Copper-nickle 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)
O-4
Canada: 1-800-387-6487
www.burndy.com
US: 1-800-346-4175
Reference
BURNDY
®