Experiment: - 5 :- Identification of Fuses and Switches

Aim To identify the types and specifications (ratings, poles, throws) of various fuses and switches using visual inspection and a multimeter.

 Part 1: Fuses

 Materials

• An assortment of fuses (e.g., glass cartridge, ceramic, automotive blade)
• A digital multimeter
• A non-conductive surface (e.g., a plastic tray or workbench)
• Safety gloves (optional but recommended)
• A magnifying glass (optional) 

Procedure

 

1. Visual Inspection: Carefully observe each fuse.

 

• Type: Classify each fuse as a cartridge, blade, or rewireable fuse based on its shape and construction.
• Ratings: Locate and record the markings on the fuse. These typically include:
• Current Rating (A): This is the amperage the fuse is designed to handle.
• Voltage Rating (V): This is the maximum voltage at which the fuse can safely operate.
• Time-Current Characteristic: Look for markings like "F" (Fast-acting) or "T" (Time-delay/Slow-blow).
• Condition: For fuses with a transparent body (like glass cartridge fuses), visually inspect the internal wire. A good fuse will have an intact wire, while a blown fuse will have a broken, burnt, or melted wire.

 

2. Multimeter Test: Use a multimeter to verify the condition of each fuse.

 

• Set-up: Set the multimeter to the continuity setting. This is often indicated by a symbol that looks like a sound wave or a diode symbol.
• Testing: Place the fuse on the non-conductive surface. Touch one multimeter probe to a metal end of the fuse and the other probe to the opposite metal end.
• Result Analysis:
• Good Fuse: The multimeter will beep or show a very low resistance reading (close to 0 Ω) on the display.
• Blown Fuse: The multimeter will not beep and will display "OL" (Over Limit) or a similar symbol, indicating an open circuit.

 

Part 2: Switches

 Materials

• An assortment of switches (e.g., toggle, push-button, rocker, rotary)
• A digital multimeter
• Connecting wires with alligator clips (optional)

Procedure

 

1. Visual Inspection: Examine each switch.

 

• Type: Identify the switch as a rocker, toggle, push-button, or rotary switch.
• Ratings: Look for stamped or printed markings that indicate the current and voltage ratings.
• Poles and Throws:
• Count the number of terminals on the switch.
• Identify the common terminal(s).
• Deduce the configuration (e.g., a switch with two terminals is typically Single-Pole, Single-Throw (SPST); a switch with three terminals is likely Single-Pole, Double-Throw (SPDT)).

 

2. Multimeter Test: Test the functionality and pole/throw configuration of each switch.

 

• Set-up: Set the multimeter to the continuity setting.
• Testing:
• SPST Switch: Connect the probes to the two terminals of the switch. When the switch is in the "OFF" position, the meter should show no continuity. When you toggle it to the "ON" position, the meter should beep or show a low resistance reading.
• SPDT Switch: Identify the common terminal (usually in the middle of a three-terminal switch). Connect one probe to the common terminal. In one switch position, test for continuity with one of the other terminals. Then, flip the switch to its second position and test for continuity with the remaining terminal. The continuity should switch between the two terminals.
• Diagram:
• Note: For switches with more complex configurations (e.g., DPST, DPDT), the same principle applies—continuity should only exist between specific pairs of terminals depending on the switch's position.