What are copper clad aluminum conductors?

Copper-clad aluminum is the newest conductor material on the market. A copper-clad aluminum conductor is drawn from copper-clad aluminum rod, the copper being bonded metallurgically to an aluminum core. The copper forms a minimum of 10 percent of the cross-sectional area of the solid conductor or of that of each strand of a stranded conductor.

Although copper-clad aluminum contains only 10 percent of copper by volume (26.8 percent by weight), its electrical performance is equivalent to that of pure copper. It is lighter and easier to handle, and the price advantage, which reflects the value of the copper content, can be as much as 25 percent when copper peaks to one of its periodic highs. Detailed studies by Battelle Laboratories have shown that copper-clad aluminum and copper have the same connection reliability.

Because the electrical industry consumes 60 percent of all copper used in the United States, it is critically affected by copper’s fluctuating costs and uncertain supply. Until recently, however, aluminum was the only alternative to copper.

Aluminum, in the more than 70 years since its introduction as an electrical conductor, has significantly penetrated such areas as electric power transmission lines, transformer windings, and telephone communications cables. On the other hand, it has received relatively limited acceptance in nonmetallic-sheathed cable and other small-gage building wires. The reason has been a lack of acceptable means of connecting or terminating aluminum conductors of 6 AWG or smaller cross-sectional areas.

Connector manufacturers, the National Electrical Manufacturers Association (NEMA), Underwriters Laboratories (UL), and aluminum companies have devoted much attention to this connection problem. The most significant advance in aluminum termination has been the institution of UL’s new requirements and testing procedures for wiring devices for use in branch-circuit-size aluminum conductors. Devices which meet the revised UL requirements are marked CO/ALR and carry that mark on the mounting strap. Only CO/ALR switches and receptacles should be used in aluminum 15- and 20-A branchcircuit wiring.

Copper-clad aluminum is now available to counter the disadvantages of high price and lack of availability of copper and the problems of connection reliability of aluminum. It is a product of a metallurgical material system, i.e., a system in which two or more metals are inseparably bonded in a design that utilizes the benefits of each component metal while minimizing their deficiencies. In copper-clad aluminum conductors, the electrical reliability of copper is combined with the abundant supply, stable price, and light weight of aluminum.

Copper-clad aluminum is already being used for building wire, battery cable, magnet wire, and radio-frequency (rf ) coaxial cable.

The ampacity (current-carrying capacity) of copper-clad aluminum conductors is the same as that of aluminum conductors. It is required that the wire connectors used with copper-clad aluminum conductors be recognized for use with copper and copper-clad aluminum conductors and be marked CC-CU or CU-AL, except that 12-10 AWG solid copper-clad aluminum conductors may be used with wire-binding screws and in pressureplate connecting mechanisms that are recognized for use for copper conductors.

Copperclad aluminum conductors are suitable for intermixing with copper and aluminum conductors in terminals for splicing connections only when the wire connectors are specifically recognized for such use. Such intermixed connections are limited to dry locations.


Production Tests
Unless otherwise specified, all production tests shall be made by the manufacturer at the factory on the complete MEI switchgear or its component for the purpose of checking the correctness of manufacturing operations and materials. (See ANSI/IEEE C37.20.3-1987.)
Production tests shall include the following:
1) Low-frequency withstand voltage tests
2) Mechanical operation tests
3) Grounding of instrument transformer cases test
4) Electrical operation and wiring tests
Low-Frequency Withstand Voltage Tests
Low-frequency withstand tests shall be made at the factory on each switchgear assembly in the same manner as described in 4.5.2 with the exception that tests across the open gap(s) (see 4.5.1(2)) are not required. Tests shall be made in accordance with 4.5.1(1) and

Drawout interrupter switch removable elements need not be tested in the assembly if they are tested separately. Control devices, potential transformers, and control power transformers, which are connected to the primary circuit, may be disconnected during the test.

Mechanical Operation Tests
Mechanical operation tests shall be performed to ensure the proper functioning of removable element operating mechanisms, shutter, mechanical interlocks, and the like. These tests shall ensure the interchangeability of removable elements designed to be interchangeable.

Grounding of Instrument Transformer Cases Test
The effectiveness of grounding of each instrument transformer case or frame shall be checked with a low-potential source, such as 10 volts or less, using bells, buzzers, or lights. This test is required only when instrument transformers are of metal case design.
Electrical Operation and Wiring Tests
Control Wiring Continuity
The correctness of the control wiring of MEI switchgear shall be verified by (1) actual electrical operation of the component control devices, or (2) individual circuit continuity checks by electrical circuit testers, or by both (1) and (2).
Control Wiring Insulation Test
A 60-Hz test voltage, 1500 volts to ground, shall be applied for 1 minute after all circuit grounds have been disconnected and all circuits wired together with small bare wire to short-circuit coil windings. The duration of the test shall be 1 second if a voltage of 1800 volts is applied. At the option of the manufacturer, switchgear-mounted devices that have been individually tested may be disconnected during this test.

Polarity Verification
Tests or inspections shall be made to ensure that connections between instrument transformers and meters or relays or similar devices are connected with proper polarities. Instruments shall be checked to ensure that pointers move in the proper direction. This does not require tests using primary voltage and current.
Sequence Tests
MEI switchgear involving the sequential operation of devices shall be tested to ensure that the devices in the sequence function properly and in the order intended. This sequence test need not include remote equipment controlled by the MEI switchgear; however, this equipment may be simulated where necessary.