What types of electrical contacts manufactured in CECL ?
Silver Electrical Contact Rivets
(Disc) Silver Electrical Contact Tips
Silver Bimetal ElectricaContact Rivets
Button Silver Electrical Contacts
(Square) Silver Electric Contact Tips
(Brazed ) Silver Electric Contacts
Tri-metal Silver Electric Contacts
Silver Electric Contacts assembles
Flap powder contacts
About Electrical Contacts
Let's begin with the basics about contact. It's also called a tip, point, finger, wedge, button and segment. A single or multi-pole product that contains movable and stationary contacts,
often including screws, springs and possibly other hardware is called a kit or set.
A contact opens and closes (makes and breaks) to engage or interrupt an electrical circuit. It's made to be replaced. It wears electrically (burning) and mechanically. It is found in switches,
relays, contactors and motor starters.
When electricity is supplied to the coil in the contactor, it acts like a magnet. This magnetic action pushes or pulls a magnetic plate that slides or claps the movable contact together
with the stationary. Please see the illustration below.
Copper only is often the material of choice when making/breaking more than one time per hour. You will often find copper-only contacts in DC applications, particularly cranes.
They don't appear to be copper, because in the great majority of cases, they have been plated. The plating can be with silver, nickel or cadmium. The plating helps prevent the
build up of copper oxide (green rust), which is non-conductive.
When closed for long periods of time (8 hours) copper only contacts have a tendency to 'stick' or weld and need silver pads of varying thickness. Generally speaking, the more
amps, the thicker the pad will be. Pure silver pads are found sometimes in DC applications. The material of choice, however, is most often silver-cadmium oxide. The mix is
usually 85/15 or 90/10. These contacts are found in most AC contactors for NEMA size 00-6. A 50/50 silver tungsten mix is used for high-amp applications. The tungsten is
very hard and often used for circuit breaker applications.
Below you'll find photos of the basic parts of a contactor. This particular example is a GE size 2, CR305D0** in the 100, 200, 300 Line. The replacement contact set is found
on page 53 in the Repco Electrical Contact catalog. The photos are from the top down, as you would take the contactor apart. The sizes of the contactor and various parts
are not in relational proportion to each other.
Why are circuit breakers and contacts coated with silver?
A silver-cadmium alloy is used much of the time, due to pure silver being very soft and subject to pitting each time the electical circuit is broken. The addition of cadmium greatly increases the hardness of the silver, which does a good job of extending the lifetime of the silver. The cadmium also greatly reduces the loss of conduction when the silver does oxidize.
Silver is used because it is the most conductive metal we have discovered. It also resists oxidizing, only doing so in the presence of sulfur, some halogens, and both nitric and sulfuric acids. The sulfur in many foods is what makes real silverware tarnish...a thin coating of sulfide is formed.