The document discusses protection devices in electric circuits, emphasizing their necessity to prevent damage from excess current. It specifically explains the characteristics of fuses, including fusing current, current rating, cut-off factor, and the materials used. Additionally, it categorizes cartridge fuses based on their rupturing capacity.

1. PROTECTION DEVICES
• Safety device used in an electric or electronic circuit
• Protects the circuit being damaged due to excess current (overload or
short circuit)
• Every circuit must be provided with a protection device.
• Commom protection devices are
Fuse
MCB
ELCB
Contactor
Relay

2. FUSES

3. What is a fuse??
• Fuse is connected in series with the circuit.

6. A

7. * Fusing current :
The current which the fuse element melts .
* current rating
Safe maximum current that can pass continuously without overheating
* Cut off factor:
Time taken by a fuse to interrupt the circuit in the event of fault
Fusing factor =Minimum fusing current/Rated current
For Re-wirable 1.4 to 1.7
For HRC 1.1
Inverse time characteristics -when current increases cut off time decreases.
Current carrying capacity of a fuse depends on thickness of wire and type of
material used.
I=k* D1.5

8. (Up to 200A)

10. Fuse element may be copper or alloy of tin(37%) and lead (63%)
Fuse material have
* Low melting point
* high conductivity
* Fuse element :
The part of the fuse which is designed to melt and open up a circuit
* Fuse
carrier
Removable portion for carrying the fuse element
* *Fuse base:
Fixed part of the fuse provided with terminals for connection to
circuit

13. Catridge Fuse (up to 1250 A)

14. Catridge Fuses can be grouped as
1. Low rupturing capacity (upto 50 KA)
2. High rupturing capacity (above 80 KA)

28. THANKYOU