GB2034536A - Electrical connection between dissimilar metals - Google Patents

Abstract

Electrical connection between two dissimilar metals, especially aluminium and copper, is effected by forming a layer of one of the metals over the surface of the other metal, whereby the interface between the dissimilar metals does not occur at the critical areas of contact used for current conduction. In the embodiment shown, copper cable 1 is crimped to a copper terminal 2 having a flat palm 6 coated on its opposite faces with aluminium. An aluminium busbar 7 is secured thereto by means of a nut 8 and bolt 9. <IMAGE>

Description

SPECIFICATION Electrical connection with bimetallic contact This invention is concerned with the corrosion problems arising when electrical connections are made between devices made of dissimilar metals, for instance when a copper cable is connected to an aluminium busbar, or vice-versa.

Corrosion problems are experienced when electrical contact is formed between dissimilar metals in a corrosive environment. Corrosion will take place even when no current is being passed, but can become very rapid indeed when electrical current is being passed. Such conditions are experienced for example, in electroplating shops, in industrial environments with corrosive atmospheres, and in ships or aircraft.

The object of this invention is to provide a method of overcoming this problem of corrosion. This object is achieved in accordance with this invention by eliminating the contact of dissimilar metals at the interface used for conduction of the current.

The present invention provides a method of forming electrical contacts between dissimilar metals by contacting a first article formed from a first metal and a second article formed from a second metal wherein said first article is provided with a coating of said second metal.

The present invention also provides an electrical device having a portion thereof formed from a first metal and adapted to be placed in electrical contact with an article formed from a second metal, wherein at least those portions of the device adapted to be in direct contact with said article are provided with a coating of said second metal.

This then brings the interface of the dissimilar metals away from the crucial conduction area to a position where corrosion is more easily controlled and also is not of such critical importance.

Instances of the differing metals to which the invention applies are aluminium conductors and equipment connected to parts made of other metals such as copper, steel or brass. For instance a copper cable may be joined to an aluminium busbar or other equipment using a copper tube terminal. In this case the palm of the connector is plated with aluminium and the inside of the tube is left as plain copper to accept the copper cable. There are therefore only contacts for current conduction between the same metals i.e. copper to copper inside the tube and aluminium at the palm.

If, on the other hand, it is required to connect an aluminium cable to a busbar or other equipment made from copper, steel, brass or other material likely to corrode aluminium, the contact can be made through a copper tube terminal plated with aluminium inside the tube and left as plain copper on the palm.

In such a combination, however, the aluminium cable may be connected to a copper busbar by means of an aluminium terminal. In this case, the palm of the terminal is placed with copper to prevent corresion of the palm in contact with the copper busbar.

In another example an electronic device such as a thyristor, diode or transistor is connected to an aluminium heatsink or electrode. The contact areas of the device itself, for instance the copper bases of "hockey puck" diodes and thyristors, are according ly plated with aluminium so as to give aluminium to aluminium contact when the connection is made.

Plating may be effected in any of the well-known ways, such as by ion plating, plasma spraying, deposition by evaporation or by electroplating from an organic or aqueous solution.

One embodiment of the invention is described by way of example in the accompanying drawing, showing in section the connection of a copper cable to an aluminium busbar in which the end of cable 1 having an insulating coating 13 is shown inside a copper tube terminal 2 into which the cable material is forced by crimped. At this point therefore there are copper to copper contact areas. The palm 6 of the tube terminal 2 is secured to an aluminium busbar 7, by means of a steel nut 8 and bolt 9, preferably aluminium coated, on which are aluminium washers 10. In accordance with the invention the outside surfaces 11 and 12 of the palm of the terminal 2 which are in contact with the aluminium busbar and washers are coated with aluminium.The gap be tween the end of terminal 2 and the end of insulation 13 is covered with a layer of a caulking composition, e.g. a silicone composition. In this way, "the copper/ aluminium conducting interface is completely pro tected from corrosive environments, by the caulking composition and there will be minimal corrosion at the contacts between busbar and terminal and between cable and terminal, both or either of which contacts may have to be initially made in the corrosive atmosphere by bolting or crimping respec tively.

1. A method of forming electrical contacts be tween dissimilar metals by contacting a first article formed from a first metal and a second article formed from a second metal wherein said first article is is provided with coating of said second metal.

2. A method as claimed in Claim 1 wherein one of said metals is aluminium and the other metal is copper.

3. An electrical device having a portion thereof formed from a first metal and adapted to be placed in electrical contact with an article formed from a second metal, wherein at least those portions of the device adapted to be in direct contact with said article are provided with a coating of said second mental.

4. An electrical device as claimed in Claim 3 wherein one of said metals is aluminium and the other metal is copper.

5. An electrical device as claimed in Claim 3 and substantially as hereinbefore described with refer ence to the accompanying Drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrical connection with bimetallic contact This invention is concerned with the corrosion problems arising when electrical connections are made between devices made of dissimilar metals, for instance when a copper cable is connected to an aluminium busbar, or vice-versa. Corrosion problems are experienced when electrical contact is formed between dissimilar metals in a corrosive environment. Corrosion will take place even when no current is being passed, but can become very rapid indeed when electrical current is being passed. Such conditions are experienced for example, in electroplating shops, in industrial environments with corrosive atmospheres, and in ships or aircraft. The object of this invention is to provide a method of overcoming this problem of corrosion. This object is achieved in accordance with this invention by eliminating the contact of dissimilar metals at the interface used for conduction of the current. The present invention provides a method of forming electrical contacts between dissimilar metals by contacting a first article formed from a first metal and a second article formed from a second metal wherein said first article is provided with a coating of said second metal. The present invention also provides an electrical device having a portion thereof formed from a first metal and adapted to be placed in electrical contact with an article formed from a second metal, wherein at least those portions of the device adapted to be in direct contact with said article are provided with a coating of said second metal. This then brings the interface of the dissimilar metals away from the crucial conduction area to a position where corrosion is more easily controlled and also is not of such critical importance. Instances of the differing metals to which the invention applies are aluminium conductors and equipment connected to parts made of other metals such as copper, steel or brass. For instance a copper cable may be joined to an aluminium busbar or other equipment using a copper tube terminal. In this case the palm of the connector is plated with aluminium and the inside of the tube is left as plain copper to accept the copper cable. There are therefore only contacts for current conduction between the same metals i.e. copper to copper inside the tube and aluminium at the palm. If, on the other hand, it is required to connect an aluminium cable to a busbar or other equipment made from copper, steel, brass or other material likely to corrode aluminium, the contact can be made through a copper tube terminal plated with aluminium inside the tube and left as plain copper on the palm. In such a combination, however, the aluminium cable may be connected to a copper busbar by means of an aluminium terminal. In this case, the palm of the terminal is placed with copper to prevent corresion of the palm in contact with the copper busbar. In another example an electronic device such as a thyristor, diode or transistor is connected to an aluminium heatsink or electrode. The contact areas of the device itself, for instance the copper bases of "hockey puck" diodes and thyristors, are according ly plated with aluminium so as to give aluminium to aluminium contact when the connection is made. Plating may be effected in any of the well-known ways, such as by ion plating, plasma spraying, deposition by evaporation or by electroplating from an organic or aqueous solution. One embodiment of the invention is described by way of example in the accompanying drawing, showing in section the connection of a copper cable to an aluminium busbar in which the end of cable 1 having an insulating coating 13 is shown inside a copper tube terminal 2 into which the cable material is forced by crimped. At this point therefore there are copper to copper contact areas. The palm 6 of the tube terminal 2 is secured to an aluminium busbar 7, by means of a steel nut 8 and bolt 9, preferably aluminium coated, on which are aluminium washers 10. In accordance with the invention the outside surfaces 11 and 12 of the palm of the terminal 2 which are in contact with the aluminium busbar and washers are coated with aluminium.The gap be tween the end of terminal 2 and the end of insulation 13 is covered with a layer of a caulking composition, e.g. a silicone composition. In this way, "the copper/ aluminium conducting interface is completely pro tected from corrosive environments, by the caulking composition and there will be minimal corrosion at the contacts between busbar and terminal and between cable and terminal, both or either of which contacts may have to be initially made in the corrosive atmosphere by bolting or crimping respec tively. CLAIMS

1. A method of forming electrical contacts be tween dissimilar metals by contacting a first article formed from a first metal and a second article formed from a second metal wherein said first article is is provided with coating of said second metal.

2. A method as claimed in Claim 1 wherein one of said metals is aluminium and the other metal is copper.

3. An electrical device having a portion thereof formed from a first metal and adapted to be placed in electrical contact with an article formed from a second metal, wherein at least those portions of the device adapted to be in direct contact with said article are provided with a coating of said second mental.

4. An electrical device as claimed in Claim 3 wherein one of said metals is aluminium and the other metal is copper.

5. An electrical device as claimed in Claim 3 and substantially as hereinbefore described with refer ence to the accompanying Drawings.