make-before-break
Of a switch or other electronic device, that creates a new electrical connection before an older one is broken.
make-before-break: the overlap that prevents dead air
A make-before-break switch establishes a new electrical path before it interrupts the old one. During the transition, both connections exist simultaneously for a brief moment. This overlap is the defining feature: current flows through the incoming circuit while the outgoing circuit is still live, then the old path drops away. The opposite design, break-before-make, cuts the old connection first and creates the new one after, leaving a gap between states.
The practical difference is stark in circuits that cannot tolerate an open line. In audio signal routing, a break-before-make changeover creates an audible click or pop as the signal path momentarily vanishes. Make-before-break eliminates that gap. Similarly, in switched telecommunications or video matrices, an instant of disconnection can drop a call or blank a display. Make-before-break contacts ensure continuity. The trade-off is that both paths carry current during transition, which can cause voltage spikes if the circuits have different potentials.
Mechanical and electronic forms
Mechanical rotary selector switches and crossbar switches were designed with make-before-break contacts by their nature: the incoming wiper arm slides into contact with the new terminal before the old one loses connection. Modern electronic implementations use semiconductor switches or relays with overlapping control signals to achieve the same effect. In field-programmable gate arrays and digital signal processors, make-before-break routing is programmed into the switching logic to prevent momentary loss of signal.
The term is common in industrial control, telecommunications, and audio/video production. In three-position selector switches, the center position often serves as the make-before-break overlap zone. Relay contact arrangements are specified explicitly in engineering drawings as MBB (make-before-break) or BBM (break-before-make) to avoid ambiguity. Cost and complexity rise slightly with make-before-break designs because additional contacts or control logic are required to create and manage the overlap window.