Protection Against Electric shock. Flashcards
Info. in here is mainly just a summary of notes. The basis of what is needed to be understood for the exam. (15 cards)
State the other word for electric shock in normal conditions.
Direct contact.
State the other word for electric shock in fault conditions.
Indirect contact.
What are the 4 measures taken to prevent electric shock in normal conditions?
Insulating live parts.
Barriers or enclosures.
Obstacles.
Placing live parts out of reach.
What are the 4 measures to prevent shock during fault conditions?
Double insulation.
Earthing and Automatic Disconnection of supply.
Electrical separation (not tested).
Extra low voltage (not tested).
What does IP stand for and what is it followed by?
Ingress Protection and it is followed by a 2 digit number.
Describe the two digit number for IP.
The first digit informs the object’s protecion from solids and the second digit, its protection from liquids.
Are power lines insulated?
No.
Define Earthing.
It means to connect all accessile conductive parts to Earth.
Define exposed conductive parts. List two examples.
All the metallic parts of an electrical system which are not normally live. Metal casing of appliances, conduit, cable tray, trunking, baskets.
Define extraneous conductive parts. List two examples.
All the metallic parts within a building which do not form part of the electrical system but can become live under fault conditions. Water, gas pipes, steel structual work, etc.
How is bonding different in comparison to earthing.
Bonding makes an electrical connection between all the metal enclosures of the installation and other metal parts that aren’t part of the electrical system. Whereas with earthing, each metal part is individually connected to the earth cable.
What are the types of Earth electrodes used?
Earth rods, pipes, lattice and plates.
What are the minimum disconnection times for 35A and above 35 A.
0.4 seconds for circuits up to 35A.
5 seconds for circuits 35A and above.
What is the main overcurrent device in an HCU normally rated at?
Rated at either 63A or 80A.
List two ways to reduce Earth electrode resistance?
Bury the electrodes deeper.
Use extendable rods.
Increase the number of rods.
Add soil conditioning agents, like rock salt.
