US 2289708 A
Description (OCR text may contain errors)
Patented July 14, 1942 ELECTRICAL CONTACT John G. Jackson, Detroit, Mich., assignor to Square B Company, Detroit, Mich, a corporation of Michigan No Drawing. Application August 2, 1940, Serial No. 350,158
This invention relates to electrical contacts for automatic electric circuit breakers and more particularly to contacts of a silver-tungsten base having substantially non-welding characteristics.
In the use of this type of contact in the past, it has been noticed that the contact resistance between the cooperating contacts would increase under certain conditions, particularly that of operation under load. This adversely afiected th use of the contacts, since the resistance increase and the heating incident thereto might reach prohibitive values. On the other hand, this type of contact is highly desirable due to its non-welding characteristics and also due to its permanency in the action of the electric are which, in the case of the automatic circuit breakers, is extremely severe in view of the heavy short circuit currents whichit is necessary to interrupt.
- of a new electric contact of a silver-tungsten base. 7
Other objects and features of the invention will be readily apparent to those skilled in the art from the following specification:
contacts, one of which is formed of silver and tungsten without appreciable proportion of carbon in any form.- The cooperating contact, however, is formed with approximately 1% by weight of carbon, preferably in the form of graphite. It has been found that when two cooperating silver-tungsten contacts are used, one of which is provided with approximately 1% of carbon and the other of which is without appreciable carbon, that the contact resistance remains within allowable values in the operation of the breaker and the other desirable features I claims:
The contacts according 'to the present invention having a silver-tungsten base may be formed either from a mixture of the powdered materials which is pressed together to form the solid contact, or a porous block of tungsten may be impregnated with molten silver. Both of these methods of forming the contacts are well known in the art and form no part of the present invention. The proportions oi. the silver and tungsten in the contacts may be greatly varied. Percentages given for example only being silver to 55% and tungsten 45% to 65% by weight, it being understood that in a mechanical mixture of this type the proportions or the elements are not critical and may be greatly varied for the different operating conditions which may be encountered. v
According to the present invention, the circuit breaker is equipped with a pair or cooperating of non-welding and resistance to the action of the are are maintained.
It is to be understoodthat the proportion of carbon in the one contact is again present mainly in the form of a mechanical mixture and that while this percentage appears to give the best result, the exact percentage is not absolutely critical but may be slightly varied within the desires of the user.
While certain preferred embodiments of this invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following What is claimed is:
1. In an automatic electric circuit breaker, cooperating contacts, one of which is formed or silver and tungsten with approximately 1% carbon and the other or which is formed of silver and tungsten without appreciable carbon present.
2. In an automatic electric circuit breaker,'cQ-
operating contacts, one of said contacts being formed of silver 35% to tungsten 45% to and carbon approximately 1% with the other or said contacts being formed of silver 35% to 55%, tungsten 45% to 65% but with substanable carbon present. 1
JOHN G. JACKSON.