Welcome to this module on control circuit components. Push button actuators and control switches. This topic covers push button actuators and control switches. A push button actuator is a type of switch that works on a simple mechanism called push to make or push to break. Actuator may be of a shrouded type or mushroom head. Mushroom head is used for emergency application and is always colored red. Shrouded type actuators are used for all other normal applications. They are available in different colors; red, green, blue, yellow, etc. Push button actuators are provided with one normally open contact or NO, or one normally closed contact or NC or one NO and one NC as standard. When necessary, a second set of contacts can be added as an option. For a START push button one NO contact shall be used. For STOP push button one NC contact shall be used. When the push button is pressed, the contacts change status from OFF to ON and remain in ON as long as the push button is in breast condition. When the finger pressing is removed, contacts return to original state. A push button has a plate that pushes down both contact plungers at the same time. A rotary selector switch has a rotating cam with ridges and allowing to actuate the plungers independently. In a rotary selector switch, the number of positions could be more depending on the application requirements. Actuation is by means of turning the knob. Only the knob visible on the panel front, and the wire able contacts are located on the rear side of the switch that is usually inside the enclosure or panel. A control switch is an electrical component which can make or break the electrical circuit manually on actuation. Control switch is also equipped with CAM operating mechanism, which makes or breaks one or more electrical circuits. There are two types of selector switches, maintained or stay put and spring return. Maintain switch or stay put switch. Once the switch is actuated by rotating the knob, the contacts relevant to that position make or break. After the hand is released, knob remains in this position and also the status of the contacts do not change. For example, when the switch knob is moved to remote position, the context relevant to remote position make, the knob remaining in remote position even after the hand is taken off from the knob. Consequently, the contacts relevant to remote position also continue to remain in closed status. Spring return switch. The knob position is controlled by a spring, and the spring ensures that the knob always stays at the neutral or central position without any external force or actuation, some contacts may make or break as long as the knob is held in actuated position. However, some contacts can be configured to remain in last status even after the most to neutral position. There are various types of control switches. CB trip, neutral closed switch or TNC switch usually comes with a pistol grip handle. It has three positions T, trip, N, neutral in the middle, and C, close. This is a spring return switch and it returns to the middle neutral position N as soon as we release our hand. Voltmeter and ammeter selector switches are stay put type. That is, they remain in the selected position until they are manually turned off. Handle maybe of oval or knob type. Typical selector positions for voltmeter, selector switches are OFF, R phase, Y phase, B phase R-Y, Y-B, and B-R. Ammeter selector switch has positions R, Y, B. In a key operated switch, once the key is removed, there is no actuator to operate the switch. Switch is a stay put type. Key lockable type switch is also a stay put type switch with pistol grip handle. It facilitates the locking in any position. The switch is lockable in local as well as remote position. If key is removed, the movement of handle is blocked. Pad lockable switch is a stay-put type and can be locked in one of the position using a padlock. Here is a quick recap of what you've learned this far. A push button actuator is a type of switch that works on a simple mechanism called push to make or push to break mushroom head PB actuator is used for emergency applications and is always colored red. Shrouded type PB actuators are used for all other normal applications and available in various colors. The control switch is CAM operated and can make or break electrical circuit. A rotary selector switch may have number of positions depending on application requirement. Two types of selector switches are maintained or stay put and spring return type. Stay put type selector switch may be key operated, lockable in one position, either by means of key or a pad lock.
