Bridge material transfer in the shape of pips and spires
The formation of pip and crater by bridge transfer is illustrated in Fig. (63.01), where it is also pointed out that this kind of transfer can lead to interlocking in the contact. The figure shows a fairly coarse pip. Finer pips are seen on Fig. (65.01). Still thinner pips, called spires, can be detrimental in modern servo mechanisms, working with milliamp, as is shown by Dallas and Stuelpnagel . They write: The first dilemma confronting the designer of sensitive contact systems occurs when he discovers that the elimination of arcs can result in a critical bridging problem. The second dilemma occurs when he starts to reduce bridge transfer by reducing current. Reducing the current diminishes the volumes of the spires but not their height; even the very thin spires are able to make sensitive relays unreliable.