480 Volt System

Question 1

if motor or circuit trips on O.C. what must you not do?

Is a ground a major concern?

If you have a ground on 480 volt system what must you not do?

Answer 1

• do not attempt to re-energize it unless cause found and fixed
  (May be waived if major plant equip is endangered)
• first ground fault could be minor, second could be catastrophic => find all grounds promptly and isolate
• do not push ground test if ground present (may cause phase to phase fault)

Question 2

What is the difference between pushing the ground test push button and the light test push button?

Answer 2

Light test- all lights should be same (if not, light is faulty)

Ground test- small ground on system => tests ground alarm, not lights (ground so small, lights not affected)

Question 3

What phase is the ground detection circuitry monitoring?

Answer 3

All, A, B, and C

Question 4

What busses on 480 volt system have curb key interlocks?

How do they work?

Answer 4

11D, E
12D, E , M , N
13D, E , J , I
14D, E
15D, E

Prevents powering bus from both S/U and AUX, only two out of three bkrs able to be closed at a time
(If bkr closed, it captures key, only two keys)

Question 5

Where does Control power come from on 480 volt loads?

Answer 5

Comes from two phases of itself (480 volt supply power)

Question 6

What is different about loads inside cnmt regarding bkr line up?

Answer 6

There is a redundant supply bkr

Backs up main supply bkr on fault (disrupt high current, protecting electrical penetration)