A
Actuation Force: The required force to change a switch from one position to another
Actuator: Mechanical part of a switch that uses mechanical force to work the switch contacts and turn the switch ON and OFF
Alternating Current (AC): Electric current which periodically reverses direction, in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences
Ampere (A): International unit of measure based on the rate of flow of electrons in an electric circuit. One ampere is equal to the amount of current that will flow through one ohm of resistance under one volt of potential. (1A = 1V / 1Ω)
Arcing: Visible electrical discharge between separated contacts that occurs each time a switch is turned on or off, except in very low voltage and low current applications. During the time of an arc very high temperatures can be reached, both in the air and on the metal of the contacts and it can burn up the contacts and reduce the useful life of the switch
B
Break-Before-Make (BBM): Double throw switch that interrupts one circuit before closing the other, leaving an interval of time between the first circuit is opened and the second circuit is closed
C
Capacitive load: A load in which the initial current on make is higher than steady state. For many purposes, it is the opposite of inductive loads
Contact Bounce: (Also referred to as Chatter) When a mechanical switch closes, the switch elements will often bounce, even if only briefly, before making final contact. This is of consequence if downstream elements are sensitive to the switching transients
Contact Resistance: Resistance to current flow, due to surface conditions and other causes, when contacts are touching one another (in the closed condition of the device)
Contacts: Conductive parts in a switch used to make and break the electrical connection
Current Rating: Maximum current in amperes, at rated current and frequency, that a device will carry continuously under defined conditions without exceeding specified performance limits. The current rating of a switch should never be exceeded. If the current rating of a switch is exceeded, the contacts may "weld" together making it impossible to open the circuit
D
Dependent Lamp: Lamp that is only lit up when the switch is in use. The lamp is powered by the same circuit that the switch is controlling. It adds one extra terminal to the switch terminal configuration
Detent: A feature that "clicks" from one active position to another rather than stalls in an intermediate position. Usually found in slide and rotary switches
Dielectric Strength: (Also referred to as Breakdown Voltage) Ability of the insulator to withstand high voltage without breaking down measure as the minimum voltage that causes a portion of an insulator to become electrically conductive
Direct Current (DC): Unidirectional flow of electric charge. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A battery is a good example of a DC power supply
Double Break: Contacts that open the circuit at two places. Having this added contact material improves heat dissipation and increases life
Double Pole-Double Throw (DPDT): Controls two separate circuits (always switched together by a single actuator), connecting each of the inputs to one of the two outputs. A DPDT switch (with no lamps) has six terminals: two for the inputs, two for the A outputs, and two for the B outputs
Double Pole-Single Throw (DPST): Controls two separate circuits but it only has one “ON” position. A DPST switch (with no lamps) has four terminals: two inputs and two outputs
Dry circuit: A low energy circuit condition where no arcing, melting or softening of the contacts occurs during contact switching. Load is so small that contact resistance does not change when the load is applied to switch
E
Electrical Life: Minimum number of cycles the switch will perform operating at full rated load without contact sticking or welding, and without exceeding the electrical specifications of the device
F
Frequency: Number of cycles per second in an alternating current (AC) sine wave. It is the rate at which current changes direction per second. It is measured in hertz (Hz), an international unit of measure where 1 hertz is equal to 1 cycle per second
G
-
H
Horsepower (hp): Unit of measurement of power (the rate at which work is done). Motors are rated in horsepower (HP) or fractions of horsepower (1/4, 1/3, 1/2, etc.) In the British Imperial System, one horsepower equals 33,000 foot-pounds of work per minute—that is, the power necessary to lift a total mass of 33,000 pounds one foot in one minute. The electrical equivalent of one horsepower is 746 watts in the International System of Units (SI)
I
Independent Lamp: Lamp that remains lit even when the switch is not in use as long as power is given to it. The lamp is powered by a voltage source not controlled by the switch action. It will add 2 terminals to the switch terminal configuration
Inductive Load: A load in which the initial current on make is lower than steady state and upon break is greater than steady state. The long arcing time, due to stored energy in the inductor at the time of breaking, is severe on the switch contacts. Devices that move and normally include electric magnets, like an electric motor
Inrush Current: Maximal instantaneous input current drawn by an electrical device when first turned on. Can cause severe degradation of contacts
Insulation Resistance: Resistance between two normally insulated metal parts, such as a pair of terminals, measured at a specific high DC potential (usually 100 VDC or 500 VDC)
J
-
K
-
L
Lamp load: (Also referred to as High Inrush load) Most notably characterized by the high inrush current at make, which may draw approximately 10 to 16 times its normal operating current when first turned on
Load: The amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy-consuming equipment of the consumer
M
Maintained Switch: Switch that maintains the mode or position to which it is actuated. If switched to the "ON" position, the switch will remain in the "ON" position until it is physically switched to another position
Make-Before-Break: Double throw switch that momentarily connects both circuits, closing the second circuit before the first circuit is opened
Momentary Switch: Switch that automatically returns to its original or at rest position. For example, a switch that automatically returns back to its resting "OFF" position when no longer actuated. Switch Components Inc. denotes momentary circuits using parenthesis. For example, OFF-(ON), where (ON) is the momentary position
N
Normally Closed: Switch that has one or more circuits that are closed when the switch actuator is at its normal or rest position. Can also be referred to as "normally ON"
Normally Open: Switch that has one or more circuits that are open when the switch actuator is at its normal or rest position. Can also be referred to as "normally OFF"
O
Ohm (Ω): Unit of measure for electric resistance. One Ohm is the amount of resistance that will allow one Ampere to flow under a pressure of one Volt
Operating Temperature: The operating temperature is the range of ambient temperature within which the device operates in
P
Poles: Number of separate circuits controlled by the switch:
- Single Pole (SP) switches control only one electrical circuit
- Double Pole (DP) switches control two independent circuits and act like two identical switches that are mechanically linked
Q
Quick Break/Quick Make: Contact with snap-acting mechanism that virtually eliminates contact teasing. Uses a compression-type spring, which provides the mechanical force to produce the snap action. Recommended for use on DC circuits
Quick Connect Tabs: Male-female connection terminals available in 3 standard widths: 250", 187“, 110" SQ. The push-on connection is made without the need for soldering, or external hardware such as nuts or screws, making for quick installation
R
Resistive Load: The easiest load to switch because current and voltage are in a steady state on make and drop instantly to zero on break. Produces minimal arcing which maximizes contact life. Resistive loads contain little or no inductance. There is a greater electrical life expectancy for a given switch in resistive load applications
S
Salt Spray Test: Standardized corrosion test method, used to check corrosion resistance of materials and surface coatings. It produces a corrosive attack to coated samples in order to evaluate (mostly comparatively) the suitability of the coating for use as a protective finish. The appearance of corrosion products (rust or other oxides) is evaluated after a pre-determined period of time
Screw Terminals: Terminals designed to affix connecting wires, fork or ring connectors to the switch by tightened screws. Provided in M3, M4, 6-32 and 8-32 configurations
Shock Test: Conducted to accurately measure the fragility of products. The data attained during these tests is key to understanding whether the product is capable of withstanding its real-world environment
Single Break / Single Make: Contacts that open and close a circuit at only one place
Slow Break/Slow Make: Contact where the physical movement of the actuator is directly linked to the physical movement of the contact. This can give very precise positioning and synchronization of both make and break points but is susceptible to arcing and intermittent signaling at the crucial make/break position, where actuator movement is slow and/or erratic. Usually associated with AC application
Solder Lugs: Terminals with which the switch is fitted with lugs, to which wires are soldered prior to panel mounting. Requires an additional, manual, step in product mounting
Single Pole-Double Throw (SPDT): Routes one input circuit to one of two output circuits. It lets you choose between two circuits, called A and B. An SPDT switch (with no lamps) has three terminals (3P): one for the input and two for the A and B outputs
Single Pole-Single Throw (SPST): Controls one circuit and connect to one output. This switch is either closed or completely disconnected. An SPST switch (with no lamps) has two terminals (2P): one for the input and one for the output
T
Terminal: The metal portion of the switch, exterior to the body, that is used to connect the switch to an electrical circuit
Throw: Number of different output connections each switch pole can connect its input to. (The number of "ON" positions that a switch has is the same as the number of throws):
- Single throw (ST) switches open or close a circuit at only one of the extreme positions of its actuator. Each pole connect to only one output
- Double throw (DT) switches open or close a circuit at both extreme positions of its actuator. Each pole connects one input circuit to one of two output circuits
​Travel: Total distance the actuator moves to change electrical position
U
-
V
Vibration test: Accomplished by introducing a forcing function into a structure, usually with some type of shaker
Volt (V): International unit of measure based on the difference in electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points
Voltage Rating: Maximum voltage allowable in the circuit in which the switch is used. The voltage rating of a switch should never be exceeded. If a voltage higher than the voltage rating of the switch is applied to the switch, the voltage may be able to "jump" the open contacts of the switch. This would make it impossible to control the circuit in which the switch was used
Wire Leads: Terminals that extend from the switch and can be attached to the circuit in whatever way is most convenient for the user
X
-
Y
-
Z
-