Have you ever wondered what the difference is between a shorting and non-shorting rotary switch?
Shorting rotary switches momentarily connect adjacent contacts during switching, while non-shorting switches ensure a clean break before making the next connection.
Understanding these distinctions is crucial when designing circuits, as the choice between shorting and non-shorting switches can significantly impact the performance and reliability of your system.
How Rotary Switches Work
Basic operation of a rotary switch
A rotary switch consists of a spindle or rotor that has a contact arm which projects from its surface. An array of terminals is arranged in a circle around the rotor, each serving as a contact for the arm. This allows the rotor to connect to any one of multiple different electrical circuits.
The rotor is turned to rotate the contact arm to different positions, making and breaking connections with the terminals. This switching action allows the rotary switch to control and configure electrical circuits by selecting between multiple preset options or settings.
Poles, throws, and positions explained
The number of separate circuits that a rotary switch can control at any given time is determined by its poles. A pole refers to each input or common terminal, with single pole (SP) switches being the most common, followed by double pole (DP) and triple pole (3P) configurations.
Throws represent the number of output positions or terminals for each pole. Rotary switches often have multiple throws, allowing them to channel the signal from each pole to multiple output terminals. The rotating contact arm channels the signal between the pole and the selected output terminal.
Rotary switch positions correspond to different combinations of poles and throws being connected. The number of positions is determined by the rotational angle between each setting. For example, a switch with 4 positions would have a 90° angle between each, while one with 12 positions would have a 30° angle.
Shorting (Make-Before-Break) Rotary Switches
Detailed explanation of shorting switch operation
In a shorting rotary switch, also known as make-before-break, the movable contact connects to the next position before disconnecting from the previous one. This means that during switching, two adjacent contacts are momentarily shorted together. The switch contact is designed to be narrower to enable this overlapping connection.
The circuit is never fully broken as the switch rotates between positions. Current continues to flow through the switch without interruption, as the new connection is “made” before the old one is “broken”.
Advantages of shorting switches
Shorting rotary switches offer several benefits in specific applications. By maintaining constant connection, they prevent arcing and avoid momentary open circuits that could disrupt sensitive electronics. This is particularly useful in audio equipment for smoothly switching between sources without causing pops or clicks
In devices like electrical testers, a shorting switch ensures the circuit under test remains connected to at least one contact point. This prevents overvoltage spikes that could damage the device or circuit being measured.
Disadvantages and potential issues
The main drawback of shorting switches is the brief connection between circuits during switching. In some situations, this momentary short could cause problems by allowing currents to flow between circuits that should remain isolated. Shorting switches are unsuitable for switching between different voltage levels, as the temporary connection could lead to damage or unintended operation.
The overlapping connections also limit the maximum switching speed and may cause increased wear on the contacts compared to non-shorting designs. Careful circuit design is necessary to ensure a shorting switch will not cause issues in a given application.
Common applications
Shorting rotary switches are commonly found in audio and video source selectors, where maintaining a constant signal path is critical for avoiding audible disruptions. They are also used in test equipment for switching between measurement points without risking high voltages on open contacts.
In some industrial control panels, shorting switches enable hot-swapping of components by ensuring a new device is connected before the old one is disconnected. This can help avoid unexpected shutdowns or equipment damage.
Non-Shorting (Break-Before-Make) Rotary Switches
Thorough description of non-shorting switch function
In a non-shorting rotary switch, also known as break-before-make, the movable contact disconnects from the previous position before connecting to the next one. This means there is a brief open circuit condition as the switch transitions between positions. The switch contact is designed to be wider to prevent any overlap or shorting of adjacent contacts.
The circuit is momentarily broken during switching, as the old connection is “broken” before the new one is “made”. Current flow is interrupted for a short period while the rotor turns to the next position.
Benefits of non-shorting switches
Non-shorting rotary switches provide isolation between circuits during switching. By ensuring the previous circuit is fully opened before the next one closes, they prevent even momentary connections between adjacent positions. This is critical when switching between different voltage levels or sensitive signals that could be damaged by a short.
In applications like speed selection or signal routing, a non-shorting switch guarantees a clean transition without any unintended mixing of circuits. The brief dead time during switching can also help prevent arcing or overloading of the switch contacts.
Disadvantages and potential issues
The main drawback of non-shorting switches is the momentary open circuit during switching. In some applications, this interruption of current flow could disrupt the operation of sensitive electronics or cause flickering in lighting circuits. Careful design is necessary to ensure connected devices can tolerate the brief power loss.
Non-shorting switches may also have a shorter lifespan compared to shorting designs, as the abrupt making and breaking of connections causes more wear on the contacts. The wider contact design can also limit the maximum number of positions available in a given switch size.
Common applications
Non-shorting rotary switches are commonly used for switching between different voltage levels, such as speed control in fans or power tools. They are also suitable for routing sensitive analog signals, like audio or sensor data, to prevent crosstalk between channels.
In test and measurement equipment, non-shorting switches enable safe switching between different test points or configurations without risk of damaging the device under test. Industrial control panels may use non-shorting switches for selecting operating modes, ensuring a clear transition between states.
Choosing Between Shorting and Non-Shorting Rotary Switches
Sensitivity of application to momentary shorts or open circuits
When selecting between shorting and non-shorting rotary switches, carefully consider the sensitivity of the connected circuits to brief interruptions or connections. In applications like audio source selection, a shorting switch maintains a constant signal path, preventing pops or clicks caused by momentary open circuits. Conversely, when switching between different voltage levels or sensitive analog signals, a non-shorting switch ensures clean transitions without any unintended mixing of circuits.
For circuits that require a continuous current flow, such as those with DC bias or LED indicators, a shorting switch avoids flickering or malfunction caused by the “dead time” of a non-shorting design. However, if the momentary short during switching could damage components or trigger unintended operations, a non-shorting switch is the safer choice.
Importance of preventing arcing
Arcing occurs when electrical current jumps across an open gap, such as between switch contacts during switching. This can cause damage to the contacts and connected components, as well as create electromagnetic interference (EMI). In applications with inductive loads or higher voltages, preventing arcing is crucial for switch longevity and circuit reliability.
Non-shorting switches are generally better at preventing arcing, as the rapid making and breaking of the circuit helps quench any arcs that may form. Shorting switches, by maintaining a continuous connection, allow more time for arcs to establish and sustain themselves. If arcing is a concern, choose a non-shorting switch or consider arc suppression techniques like snubber circuits or zero-cross switching.
Switch rating, reliability, and longevity needs
Rotary switch ratings, including maximum voltage, current, and power, must match or exceed the requirements of the application. Overloading a switch can lead to premature failure or even dangerous conditions like fire or electric shock. Always check the manufacturer’s specifications and derate the switch if necessary based on the operating environment and duty cycle.
Shorting switches typically have a longer lifespan than non-shorting designs, as the gradual making and breaking of connections causes less wear on the contacts. However, this advantage may be negated in applications with frequent switching or high inrush currents, where the non-shorting design’s quick disconnect can help protect the contacts.
Consider the expected service life and maintenance requirements when choosing a rotary switch. For critical applications or those with difficult access for replacement, a high-reliability switch with a longer rated life may be worth the added cost. Gold-plated contacts, sealed housings, and robust detent mechanisms can all contribute to improved switch reliability and longevity.
FAQs
1.Can a shorting switch cause a short circuit fault?
A shorting switch itself does not inherently cause short circuit faults. Short circuits are abnormal low-resistance connections that allow excessive current. Shorting switches briefly connect circuits during switching, but this is normal operation, not a fault condition.
2.How long is the “dead time” in a non-shorting switch?
The “dead time” in a non-shorting switch is typically very brief, lasting only a fraction of a second. The exact duration depends on factors like the switch’s rotational speed and the gap between contacts. In most applications, this momentary interruption is negligible.
In Conclusion
Understanding the differences between shorting and non-shorting rotary switches is essential for designing reliable and efficient electrical systems. Each type has its advantages and disadvantages, making it crucial to select the appropriate switch for your specific application.
When choosing a rotary switch, carefully consider the circuit requirements and potential impacts of momentary shorts or open circuits. Make an informed decision to ensure optimal performance and longevity.
