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Skills Assessment > MCC Motor Control Centers > Flashcards

MCC Motor Control Centers Flashcards

1
Q

Discuss the risks of arc-flash

A

An electrical explosion resulting from current traveling to ground or phase to phase. Heat, flying debris, shock wave, and vaporized metal can cause injury or death.

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2
Q

Risks for electrocution from 480v bucket?

A

Connected to main buswork. possibility of multiple voltage souces and levels.

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3
Q

Risks of electrocution from control wiring?

A

Multiple voltage sources. Usually 120VAC.

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4
Q

Risks of electrocution from UPS systems?

A

Voltage may be present even after isolationg the equipment. Multiple voltage sources. DC battery side of circuit has very high current available.

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5
Q

Risks of electrocution from distribution panels?

A

Hazardous when removing the cover and voltage checking.

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6
Q

What is the significance of grounding?

A

Grounding is used to provide a solid path for stray current to travel. This enables current overload devices such as fuses and breakers to sense unsafe current situation and shut off power.

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7
Q

What is the imprtance of isolation procedures?

A

Electrical isolation protects personnell from shock and unintended motion of equipement.

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8
Q

What is the most important piece of equipment needed when troubleshooting a MCC?

A

Multimeter.

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9
Q

What is the first thing you would use a meter for when troubleshooting an MCC?

A

Verify that no voltage is present.

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10
Q

What is a multimeter used for when troubleshooting a MCC?

A

Wire continuity.
Open or closed contacts.
Open fuses.

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11
Q

When equipment won’t start, what are common faillures to look for?

A

Tripped breaker.
Blown fuse.
Tripped overload.
Defective control circuit.

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12
Q

If the circuit breaker is tripped or a fuse is blown, what should be done prior to energizing the circuit? Why?

A

Verify that none of the phases are going to ground. The breaker could explode or the fuse blown again.

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13
Q

What are potential causes of tripped overloads?

A

Overloading of the motor - caused by any number of things.

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14
Q

What diagram can be used for troubleshooting?

A

Sigle line or motor schematic.

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15
Q

When sdhould the LOTO procedure be usded?

A

When contact with energized conductors is possible or motor movement could cause injury.

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16
Q

What PPE is needed when working on an energized MCC?

A

Gloves, hood, flash suit, arc-rated face sheild.

17
Q

What is the purpose of an IR scan?

A

Loose connections and overloaded equip[ment can be found with their heat signatures.

18
Q

Where do you find National Electrical Code (NEC) Standards?

A

NFPA 70E for behaviors, NFPA 70 for wiring methods.

19
Q

What does MCC stand for?

A

Motor Control Center

20
Q

What does an MCC normally control?

A

Motors, pumps, compressors, fans, lights, etc.

21
Q

What are some components in an MCC compartment?

A

Fuses, breakers, control voltage transformer. contactor, motor starter, control wiring, overload protection, pilot lights, push buttons.

22
Q

What is the purpose of overload protection?

A

To protect a motor if it starts to overamp.

23
Q

What informatyion would you need to size overloads?

A

Full load current off of the motor and wire size.

24
Q

What is the purpose of a breaker?

A

A breaker disconnects power in case of a fault/short-circuit.

25
Q

How do you know what the control voltage is?

A

Listed on the motor started anmeplate or test using meter.

26
Q

If you have a 480 VAC bucket and the starter coil is 120 VAC, what will you need to make this starter work?

A

Control transformer, fuses, etc.

27
Q

What information do you need before you can size a starter?

A

Motor HP.

28
Q

Can you trust the pilot light to tell you if the motor is running or not?

A

No, the pilot light can burn out, the motor starter could weld closed.

29
Q

What is a dual element, time delay fuse?

A

A fuse with two elements. One made for short time-high voltage events like a short curcuit and the second for overload monitoring over time.

30
Q

How can THD (Total Harmonic Distortion) affect your electrical system? How do you determine THD?

A

Additional heating of electrical system components can damgae or shorten the lifespan of equipment. Osiliscope, or power quality analyzer.

Skills Assessment (10 decks)

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