Elecrical Safety

Question 1

Electric arch temperatures

Answer 1

-typically reach 3500 degrees C

Question 2

Approach distance

Answer 2

-7m from power lines when working or operating machinery.

Question 3

Circuit Breakers

Answer 3

• open the circuit they are protecting in the event of a short circuit or high current level overload.
• basic types of faults are high energy, short circuit faults and longer duration overload faults.

Question 4

Different types of circuit breakers

Answer 4

• single pole, single phase (house hold)
• three phase auxillary (welders and grinders)
• motor (on the MCC in industry)

Question 5

Interrupter Rating vs. Fuse Rating

Answer 5

• fuses are rated by: voltage rating, current and amp rating, interrupting rating and blow characteristics.
• interrupting rating is the maximum current the breaker can safety interrupt without failure.

Question 6

Stop buttons

Answer 6

-always wired closed

Question 7

Types of fuses

Answer 7

• fast acting which blow instantly and rapidly when their current rating and blow characteristics are exceeded.
• Time delay which have thermal delay fusible links and also instant blowing links for high level faults.

Question 8

Ampacity

Answer 8

-the allowable current carrying capacity of a wire or cable assembly

Question 9

Thermal overload relays

Answer 9

• emulating the temperature of the motor windings that they protect
• two kinds are bimetallic and melting alloy

Question 10

Bimetallic relays

Answer 10

-use a heater element to detect the amount of current flowing. When the current exceeds it, the heater causes the element to bend.

Question 11

Melting Alloy Relay

Answer 11

-use a pot filled with a low temp melting alloy fastened to the current carrying bar to sense the temp of the motor windings. When the temp exceeds the alloy melts

Question 12

Conventional Flow vs. Electron flow

Answer 12

-conventional is positive to negation and electron is negative to positive

Question 13

Line voltage tolerance

Answer 13

+- 5%