Terminology For Over Current Protection Devices

Short Circuit:

•  a short is a larger than normal current which flows outside its normal current path

•  protection devices for this type respond as quickly as possible

•  Term Used: Overcurrent Protection

Overload:

•  is a current larger than normal but still flowing within its normal path, normal range within 1 to 6 times normal current ( FLA )

•  protection devices for this type must respond rather slowly

•  Term Used: Overload Protection

Protection of Overcurrent or Overload Devices:

•  devices must be placed on series with the circuit being protected and must automatically open the circuit it current exceeds designed levels.

Forms of Overcurrent Protection:

•  Fuses

•  Plug or Cartridge

•  Circuit Breaker

•  Magnetic

•  Thermal

•  Thermal-Magnetic

Fuse:

•  A fuse is designed to be the weakest link in an electrical circuit

•  It is a heat sensitive device that contains a strip of metal alloy that melts before the circuit conductors exceed their amp rating thus providing electrical protection for that circuit

 

Types of Fuses:

 

Plug Fuse:

•  normally used in Residential Wiring for stoves

•  Blue for 15 amps

•  Pink for 20 amps

•  Red for 25 amps

•  Green for 30 amps

•  Green 30 amps plugs are the Max Size plugs

 

•  Note: Plug Fuses are non-renewable (one time fuse) max Voltage rating of 150 volts to ground

 

Cartridge Fuses:

•  Cartridge type fuses come in TWO FORMS

•  Single Elements

•  Dual Element (time delay)

•  Note: the longer the fuses length the high the voltage

 

•  One time Use or Renewable link Ferrule contact or Knife Blade

 

•  Ferrule Type: used up to 60 amps, voltage rating 250 volts, 300 volts or 600 volts

 

•  Knife Type: used for ratings over 60 amps to a max of 600 amps voltage rating 250 to 600 volts

 

•  Note:

•  the above cartridge fuses are classified as Standard Code Fuse which has an Interrupting Capacity of 10,000 amps

•  High rupturing Capacity (HRC) which has and Interrupting Capacity of 100,000 amps

•  Two Forms of HRC Fuses

•  Form 1 HRC: provides for both Overload and Overcurrent protection (time delay)

•  Form 2 HRC: provides for Overcurrent Protection Only (not time delay)

Circuit Breaker:

•  the CEC defines a Circuit Breaker as an Electro Mechanical Device designed to open a current carrying circuit under both Overload and Overcurrent conditions

•  The CEC also requires that Circuit Breakers be Trip Free

 

Types:

•  thermal

•  magnetic

•  thermal-magnetic

•  thermal breaker

 

•  a thermal breaker has a thermal element connected in series with the contacts

•  ITS FUNCTION IS TO PROTECT the CIRCUIT against OVERLOAD CONDITIONS

•  Note: DO Not use in applications where instantaneous response to Overcurrent is required

 

Magnetic Breaker: (ACR used for time delay thermal magnetic)

•  a magnetic breaker has a an electromagnet connected in series with the contacts ITS FUNTION IS to PROTECT the CIRCUIT against OVERCURRENT CONDITION

•  NOTE: Will Not Provide Overload Protection

Thermal-Magnetic Breaker:

•  a thermal-magnetic breaker has a thermal element as well as a electromagnetic in series with the contacts.

•  IT FUNTION IS to PROTECT the CIRCUIT against OVERLOAD as well as OVERCURRENT CONDITIONS

Rating of Circuit Breakers:

•  Voltage

•  Interrupting Capacity

•  Frequency

•  Continuous Current