Questions and Answers
What does a motor overload relay consist of?
A current-sensing unit and mechanism activated by the sensing unit.
What should low-voltage and high-voltage cables be separated by when placed in parallel runs?
At least 6 inches.
What type of contacts are normally open (NO) on magnetic contactors?
Contacts that are apart when the relay is de-energized.
What are lighting contactors rated for?
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What do low-voltage remote control switching relays use?
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Which of the following can provide motor overload protection but have the disadvantage of being nonrenewable?
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What type of device can multiply the switching function of a pilot device?
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What are the two classifications of overload relays?
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How do you reverse the rotation of a motor?
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Why are mechanically held relays and contactors often used?
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Which of the following relays is resistant to shock and vibration, commonly used for the I/O track of a programmable controller?
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What can the lubrication of a motor be accomplished using?
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If contactor action is dependent on current flow, what is the contactor described as?
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What do melting alloy and metallic overload relays react to?
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What is the normal control voltage range for solid-state relays?
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What is a probable cause of relay-controlled equipment failing to start when the contactor is closed?
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Where should the panel for a low-voltage lighting control system enclosure be mounted?
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What is the result of increasing the armature spring force in a relay?
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Study Notes
Motor Overload Relays
- Consist of a current-sensing unit and a mechanism that opens the motor circuit when activated.
- Designed to protect motors from overheating by disconnecting the power in case of overload.
Cable Placement
- Low-voltage and high-voltage cables placed in parallel must be separated by at least 6 inches.
- Separation is crucial to protect low-voltage conductors from electromagnetic noise.
Magnetic Contactors
- Normall open (NO) contacts remain apart when the relay is de-energized.
- Used in various applications to control power delivery.
Lighting Contactors
- Rated to handle high inrush currents, which are significant when lighting systems are activated.
- Essential for managing the initial surge of electricity when lights are turned on.
Low-Voltage Remote Control Switching Relays
- Utilize a split coil to control operations remotely.
- Provide a means for easy operation of electrical devices from a distance.
Motor Overload Protection
- Dual-element or time-delay fuses can provide motor overload protection.
- They are nonrenewable, meaning they must be replaced after a fault occurs.
Control Relay
- An electromagnetic device that multiplies the switching function of pilot devices.
- Enhances the control capabilities within electrical systems.
Overload Relay Classifications
- Overload relays are classified into two types: thermal and magnetic.
- Thermal relays react to heat generated by excess current, while magnetic relays respond to current levels.
Motor Rotation
- To reverse a motor's rotation, connect L1 to motor terminal T3 and L3 to terminal T1.
- Proper connections are critical for the desired motor function.
Mechanically Held Relays
- Preferred for their quieter operation compared to electrically held devices.
- Often used when noise reduction is important in an application.
Solid-State Relays
- Resistant to shock and vibration, making them suitable for the I/O track of programmable controllers.
- Typically have control voltages ranging from 3V to 32V.
Motor Lubrication
- Timing relays can be utilized for scheduling lubrication at specified intervals.
- Ensures motors operate smoothly and decreases wear and tear.
Relay Functionality
- Relays that depend on current flow for action are described as electrically held.
- Their operation is contingent upon the presence of electrical current.
Overload Relay Types
- Melting alloy and metallic overload relays react to fluctuations in motor load current.
- Essential for maintaining motor health and preventing damage.
Contact Issues
- A probable cause of relay-controlled equipment failing to start is one contact not closing properly.
- Ensuring all contacts operate correctly is vital for reliable equipment functionality.
Low-Voltage Lighting Control System Panels
- Should be mounted at eye level between two studs for easy access and visibility.
- Layout considerations help in maintaining user-friendly system access.
Relay Armature Spring Force
- Increasing the armature spring force results in higher drop-out values.
- This adjustment can affect the relay's responsiveness to changing conditions.
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Description
Test your knowledge with these flashcards covering crucial concepts from Electricity Level 2, Section 11. Each card features important terminology and definitions related to electrical systems, such as motor overload relays and cable separation for noise protection. Perfect for students and professionals alike seeking to reinforce their understanding in the field of electricity.
