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17 Cards in this Set

  • Front
  • Back

What formula do you use to calculate line current in a motor

Input power/square root of 3 x voltage of load x pf

How do you calculate pf in a motor

Pf= cos plus the phase angle


Or P/S in the motor triangle

How do you calculate slip speed

Synchronous speed x slip %

What is a BJT in terms of semi conductors

Bi-polar junction transistor

What earth fault loop tests need to be carried out

Tests to ensure protection final sub operates in required time

Why is the resistance of the protective earthing conductor of a flexible cord on a class on appliance set to a maximum of 1Ohm

• under fault conditions, it prevents the touch voltages rising to a danger level


• to ensure sufficient fault current flows to operate protective devices

Define the term cut off characteristic

This is the value of fault current that cuts off the fuse that is less than the perspective short circuit current

Define the term total clearing time

This is the time it takes to interrupt the flow of current and extinguish the arc

Formula for calculating line current in a transformer

VA/ square root of 3 x line voltage

Define the term cut off characteristic

This is the value of fault current that cuts off the fuse that is less than the perspective short circuit current

Define the term total clearing time

This is the time it takes to interrupt the flow of current and extinguish the arc

Formula for calculating line current in a transformer

VA/ square root of 3 x line voltage

Define the term cut off characteristic

This is the value of fault current that cuts off the fuse that is less than the perspective short circuit current

Define the term total clearing time

This is the time it takes to interrupt the flow of current and extinguish the arc

Formula for calculating line current in a transformer

VA/ square root of 3 x line voltage

Why is the earth fault loop impedance test carried out at the socket furthest away from the switchboard

• to confirm that the electrical protection will operate in required time


•to confirm that electrical protection on all other final sub circuits supplied from the main switchboard will operate in required time

How do you calculate KW

KW = VA / of