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The current in amperes that a conductor can carry continuously under the conditions of use without exceeding its temperature rating
Ampacity
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The permanent joining of metallic parts or circuits assuring electrical continuity and capacity to safely conduct any current likely to be imposed
Bond
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Device used to completely disconnect a circuit when any abnormal condition exists.
Circuit breaker
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Any wire, cable, or substance capable of carrying an electrical current
Conductor
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A device that protects a circuit from an overcurrent condition only. It has a fusible link directly heated and destroyed by the current passing through it
Fuse
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A conducting connection, whether intentional or accidental, between a circuit and piece of equipment, the earth, or some body serving as earth; a place of zero electrical potential
Ground
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The voltage between any given conductor and any point at ground potential
Ground voltage
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Voltage above 15,000 volts
High voltage
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Voltage between 15,000 and 600 volts
Intermediate voltage
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A current-carrying conductor intended to deliver power to or from a load normally at an electrical potential other than ground
Leg
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600 volts or less
Low voltage
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Suited for circuits rated at 600 volts or lower
Low voltage circuit breaker
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Control device used to de-energize the motor in a low voltage condition and keep it from re-starting automatically upon return of normal voltage
LVP controller
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Control device used to de-energize the motor in a low voltage condition and restart the motor when normal voltage is restored
LVR controller
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Control device maintains the motor across the line at all times
LVRE controller
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Provides control and protect for the operation of a motor
Motor controller
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A current-carrying conductor normally tied to ground so that the electrical potential is zero
Neutral
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The greatest root mean square (effective) difference of potential between any two legs of the circuit
Phase voltage
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Designed to cause the prompt removal of any part of a power system that might cause damage or interfere with the effective and continuous operation of the rest of the system
Protective relays
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Any failure that may occur within a given zone will cause the tripping or opening of all circuit breakers within that zone
Zone of protection
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Explain the following terms as they apply to Electrical Distribution Systems
- Single-line (one-line) diagram
- Commercial or utility power
- Diesel power
- Failure-free power
- Neutral grounding
- Voltage class
- Protective relays
- Overlapping protective zones
Single-line diagram - simple and easy-to-read diagram showing power supplies, loads, and major components in the distribution system.
Commercial or utility power - electric power supplied to the facility
Diesel power - economical/practical source of standby power
Failure-free power - power supplied to vital equipment with automatic switching so that interruption of power is minimized
Neutral grounding - helps prevent accidents to personnel and damage to property by fire
Voltage class - high voltage > 15,000 volts, intermediate voltage is 600-15,000 volts, low voltage # 600 volts
Protective relays - cause prompt removal of any part of a power system that suffers a short circuit
Overlapping protective zones - created around each element of the power system to prevent element failure from interrupting the whole system operation
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Describe the protection provided by each of the following
- Breakers
- Fuses
- Protective relays
- Breakers - disconnect component from the power system
- Fuse - protects component from overcurrent
- Protective relays - cause prompt removal of any part of a power system that suffers a short circuit
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State the purpose of circuit breakers
The purpose of a circuit breaker is to provide a means for connecting and disconnecting circuits of relatively high capacities without causing damage to them.
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Given a simple schematic of a circuit breaker control circuit, describe the operation of that breaker during remote operation and automatic tripping
- The three most commonly used automatic trip features for a circuit breaker are overcurrent, underfrequency, and undervoltage.
- If any one of the conditions exists while the circuit breaker is closed, it will close its associated contact and energize the tripping coil, which, in turn, will trip the circuit breaker.
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List the three most widely used protective features that may be incorporated into a circuit-breaker control circuit
The three most commonly used automatic trip features for a circuit breaker are overcurrent, underfrequency, and undervoltage
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State the function of motor controllers
Motor controller - controls and protects the operation of a motor
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State three protective features (overloads) that may be incorporated into a motor controller
Controller’s protective features - fuses, thermal overloads, and magnetic overloads
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Given a simplified drawing of a motor controller, describe the operation of that motor controller
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- 4-Wire Three Phase Wye System Neutral connected Node.
- Safest Possible Multi-purpose distribution system
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