Drive Applications, Selection, and Engineering Decisions

Introduction

An electrical drive is a coordinated system that converts electrical energy into controlled mechanical motion. It normally includes a motor, power converter, controller, sensors, protection, mechanical transmission, and the driven load. Selecting a drive is therefore not simply a matter of choosing a motor with sufficient power. The engineer must match the complete system to the load’s torque–speed requirement, duty cycle, dynamic performance, environment, safety obligations, energy objectives, and maintenance strategy.

In mechatronics, drive selection affects positioning accuracy in robots and CNC machines, production rate in conveyors, ride quality in elevators, energy consumption in pumps and fans, and range and thermal safety in electric vehicles. A technically functional but poorly selected drive may exhibit overheating, unstable control, excessive vibration, electromagnetic interference, premature bearing failure, or unacceptable lifecycle cost.

Learning Objectives

After completing this chapter, the student should be able to:

1. Classify loads according to their torque–speed characteristics and duty cycles.
2. Select motors, converters, feedback devices, and braking systems for common applications.
3. Evaluate drives using performance, efficiency, reliability, safety, maintainability, and lifecycle cost.
4. Explain application-specific requirements for robotics, CNC systems, pumps, fans, conveyors, elevators, renewable generation, electric vehicles, and automation.
5. Develop and justify an engineering drive-selection decision.
6. Identify limitations, standards, hazards, and emerging technologies relevant to drive integration.

1. The Drive as an Engineered System

A modern drive consists of several interacting subsystems:

• Energy source: utility supply, battery, DC bus, or renewable generator.
• Power converter: rectifier, inverter, chopper, or bidirectional converter.
• Motor: induction, permanent-magnet synchronous, synchronous reluctance, brushed DC, or another machine.
• Control system: regulates speed, torque, position, current, voltage, or power.
• Feedback: encoders, resolvers, Hall sensors, tachometers, current sensors, and temperature sensors.
• Mechanical interface: coupling, gearbox, belt, ball screw, rack-and-pinion, wheel, drum, or pump impeller.
• Protection and safety: circuit protection, overload detection, safe torque off, emergency stopping, guarding, and thermal supervision.

The system boundary should include the load and its mechanical transmission. A motor that appears suitable at its shaft may be unsuitable after gearbox losses, reflected inertia, shock loading, or regenerative operation are considered.

For rotational motion, mechanical power is

where P_m is mechanical power in watts, T is torque in newton-metres, and ω is angular speed in radians per second. If speed is specified in revolutions per minute, n, then

This relationship assumes a rotating shaft and uses radians per second for angular velocity. A useful engineering form is

where torque is in N·m, power P_kW is in kW, and speed n is in r/min. The constant 9550 follows from unit conversion and is appropriate for mechanical shaft power.

The drive must satisfy both steady-state and transient requirements. Steady-state requirements include continuous torque, speed, power, efficiency, and thermal equilibrium. Transient requirements include acceleration, deceleration, reversing, disturbance rejection, positioning, and peak torque.

2. Load Characterisation

2.1 Torque–speed laws

The first selection task is to identify how load torque changes with speed.

For a centrifugal pump or fan, the affinity laws for geometrically similar operation are approximately

where Q is flow rate, H is head or pressure-related energy, and P is shaft power. These laws assume similar operating conditions and are not exact near shutoff, cavitation, or strongly altered system curves. They explain why speed control can provide substantial energy savings.

2.2 Inertia and acceleration

The total inertia seen by the motor includes the motor rotor, coupling, gearbox, and load reflected through the transmission. For an ideal gearbox with speed ratio i = ω_m/ω_L, load inertia reflected to the motor is

where J_L is load inertia and J_L,ref is the equivalent motor-side inertia. This assumes negligible gearbox compliance and loss. A large inertia ratio increases acceleration time and may require a higher peak torque rating.

The dynamic torque equation is

where T_m is motor torque, T_L is opposing load torque, J_eq is equivalent rotational inertia, and α is angular acceleration. Friction and transmission losses should be added to the resisting torque in a practical model.

2.3 Duty cycle and thermal selection

Motor ratings are meaningful only with a duty description. Common duty patterns include continuous operation, short-time operation, intermittent periodic operation, and highly variable loads. The motor’s thermal stress depends on current, speed, cooling, ambient temperature, and the duration of overloads.

For a sequence of constant-torque intervals, an approximate equivalent torque for heating is

where T_i is torque during interval i and t_i is its duration. This is an approximation based on copper-loss heating proportional to current squared and torque approximately proportional to current. It should not replace the manufacturer’s thermal model when cooling varies significantly with speed.

The motor should satisfy both

and

with suitable margin. Excessive oversizing can reduce efficiency and power factor at light load, increase cost, and impair dynamic response.

3. Choosing the Motor and Converter

Induction motors

Induction motors are rugged, economical, widely available, and suitable for pumps, fans, compressors, conveyors, and many industrial machines. With a variable-frequency drive, speed is controlled by changing stator frequency while maintaining an appropriate voltage-to-frequency relationship. Sensorless vector control can provide good torque control, whereas encoder feedback improves low-speed and positioning performance.

Permanent-magnet synchronous motors

Permanent-magnet synchronous motors offer high efficiency, high torque density, and excellent dynamic performance. They are common in robotics, servo systems, electric vehicles, and high-efficiency industrial equipment. Their disadvantages include magnet cost, possible demagnetisation under severe fault or thermal conditions, and the need for sophisticated control. Regeneration can occur readily, so the inverter and DC-link energy management must be designed accordingly.

Synchronous-reluctance motors

Synchronous-reluctance motors avoid permanent magnets and can provide high efficiency with suitable rotor design and control. They are attractive where magnet supply, cost, or high-temperature considerations are important, although acoustic noise, torque ripple, and control requirements must be evaluated.

Brushed DC motors

Brushed DC motors provide straightforward torque control and high starting torque. Brushes and commutators, however, require maintenance and limit operation in dusty, explosive, or high-speed environments. They remain useful in low-cost actuators and legacy systems but are frequently replaced by electronically commutated machines.

Power converters and control modes

A converter must be selected for voltage, current, overload, switching frequency, regenerative operation, harmonic performance, cooling, and network compatibility. Important control modes include:

• Scalar control: simple and economical; appropriate for many fans and pumps.
• Sensorless vector control: improved torque regulation without a mechanical sensor.
• Closed-loop vector control: high torque accuracy and low-speed performance.
• Servo control: coordinated current, speed, and position loops for precise motion.
• Direct torque control: rapid torque response, with implementation-dependent ripple and switching behaviour.

The converter current rating must reflect motor current, overload duration, ambient temperature, altitude, switching frequency, and application class. A converter’s nominal kW rating alone is insufficient.

4. Application-Specific Selection

4.1 Robotics

Robotic joints require high torque density, low reflected inertia, smooth low-speed operation, repeatable positioning, and controlled braking. Servo motors are usually paired with high-resolution encoders or resolvers and a reduction transmission such as a harmonic, planetary, or cycloidal gearbox.

Selection must consider payload, reach, joint acceleration, gravity torque, collision detection, cable routing, backlash, and thermal duty. Gravity-loaded joints may require continuous holding torque even when stationary. A normally energized brake or a counterbalance may be required to prevent a vertical axis from falling after power loss.

The robot controller must coordinate current, velocity, and position loops. Encoder errors, gearbox compliance, and structural flexibility can create oscillation. Safety-rated monitored stop, reduced-speed operation, and force or torque limitation are important where humans and robots share a workspace.

4.2 CNC machine tools

CNC systems generally use servo drives for feed axes and a separate spindle drive. Feed axes demand high stiffness, rapid acceleration, low following error, and precise interpolation. Ball screws, linear motors, or rack-and-pinion systems may be used depending on travel and speed.

The spindle drive must provide a broad speed range, constant torque below base speed, and approximately constant power above base speed. Tool changes, tapping, cutting shocks, and regenerative deceleration impose transient demands. Encoder feedback may be required for rigid tapping and spindle orientation. Bearing preload, vibration, thermal growth, and electromagnetic compatibility influence machining accuracy.

4.3 Pumps and fans

Centrifugal pumps and fans are classic variable-torque applications. Variable-speed drives allow the operating point to follow process demand rather than throttling flow with a valve or damper. Energy savings are especially significant when speed is reduced, because ideal shaft power varies approximately with the cube of speed.

The engineer must still check minimum flow, pump cooling, lubrication, cavitation margin, resonance, motor cooling at low speed, and water-hammer effects during ramps. Constant-pressure control often uses a pressure transducer and a feedback controller. The drive should prevent dry running and excessive cycling.

4.4 Conveyors

Conveyors commonly require constant torque and may have high breakaway torque when loaded. Selection includes belt or chain friction, material mass, incline, acceleration time, starting frequency, and jam conditions. Multiple conveyor sections may require coordinated speeds to avoid product accumulation.

A soft starter may be sufficient for simple fixed-speed systems, while a variable-frequency drive is preferable where speed variation, controlled starting, or energy management is required. Long conveyors may need braking resistors or regenerative converters during downhill operation. Mechanical brakes and emergency-stop circuits must be designed independently of ordinary software stopping.

4.5 Elevators and hoists

Elevators are safety-critical, four-quadrant applications. The drive must control acceleration, constant-speed travel, deceleration, leveling, and load-dependent torque. Counterweights reduce average motor power but do not eliminate worst-case torque conditions.

Regenerative operation occurs while lowering a heavy car or raising a light one. Returned energy can be fed to the building supply, stored in a common DC bus, or dissipated in a braking resistor. A mechanical brake normally holds the car when the drive is disabled; it must not be treated as the sole means of normal speed control. Overspeed protection, brake monitoring, emergency operation, and inspection modes must comply with applicable elevator standards and local regulations.

4.6 Renewable generation

Wind turbines and variable-speed hydro systems use drives or power converters to decouple generator speed from grid frequency and to control active and reactive power. A doubly fed induction generator uses a partially rated converter connected to the rotor, whereas a permanent-magnet generator commonly uses a full-scale converter.

Photovoltaic systems use maximum power point tracking to select the voltage and current at which array power is maximised. Grid-connected converters must satisfy synchronization, anti-islanding, harmonic, fault-ride-through, and protection requirements. Reliability is strongly affected by thermal cycling, humidity, lightning, and power semiconductor stress.

4.7 Electric vehicles

An electric vehicle traction drive combines a battery, contactors, inverter, motor, reduction gear, differential, braking system, and vehicle control unit. It requires high peak torque for launch, high efficiency over a changing duty cycle, regenerative braking, wide speed range, low acoustic noise, and safe isolation from the chassis.

Permanent-magnet synchronous motors provide strong torque density; induction and reluctance machines may offer cost or high-speed advantages. The inverter must manage battery voltage variation, current limits, thermal constraints, and field weakening. Regenerative braking is limited by battery state of charge, temperature, traction, and charging power. Friction brakes remain necessary for emergency and low-speed braking.

4.8 Factory automation

Automation applications range from indexing tables and packaging machines to automated guided vehicles and process lines. Selection depends on synchronization, cycle time, repeatability, networking, diagnostics, and safety functions. Distributed drives connected through industrial Ethernet can coordinate motion while reducing wiring, but network latency and failure behaviour must be analysed.

5. Engineering Decision Criteria

Performance

Performance includes speed range, torque accuracy, acceleration, settling time, positioning error, stiffness, noise, vibration, and response to disturbances. A drive should be assessed against the actual motion profile rather than an isolated catalogue rating.

Efficiency and power quality

Overall efficiency is

where P_out is useful mechanical output power and P_in is electrical input power. If motor, converter, gearbox, and auxiliary efficiencies are represented separately,

provided the power-flow directions and definitions are consistent. Harmonic currents, poor power factor, standby consumption, and cooling-fan power should be included in serious evaluations.

Reliability and maintainability

Reliability is influenced by thermal stress, bearings, insulation, power semiconductors, connectors, sensors, contamination, vibration, and software. Mean time between failures is useful for comparison but does not guarantee field performance. Maintainability includes access, modular replacement, diagnostic quality, spare-parts availability, lubrication requirements, and technician competence.

A practical design includes condition monitoring for temperature, vibration, current imbalance, insulation degradation, encoder health, and DC-link abnormalities. Predictive maintenance should support—not replace—sound mechanical inspection and safety procedures.

Lifecycle cost

Lifecycle cost should include purchase, installation, commissioning, energy, maintenance, downtime, replacement, disposal, and training. A simplified present-value model is

where C₀ is initial cost, N is analysis life in years, r is the discount rate, and the annual cost terms are expressed in consistent currency units. This model assumes costs can be estimated by year and discounted financially; uncertainty should be tested with sensitivity analysis.

For example, suppose a drive retrofit costs $18,000 initially and saves $6,000 per year for four years, with $1,000 annual maintenance cost and a discount rate of 8%. The annual net benefit is $5,000. The present value of benefits is

The simple present-value balance is approximately $16,560 − $18,000 = −$1,440, excluding residual value and downtime savings. Thus, the retrofit is not justified on energy and maintenance alone under these assumptions, although production or reliability benefits might change the decision. The simple payback is 18000/5000 = 3.6 years, but payback alone ignores discounting and risk.

Safety and compliance

Drive integration must address electrical shock, arc energy, unexpected startup, stored energy, rotating machinery, braking failure, and loss of feedback. Safety-related functions may include emergency stop, safe torque off, safe stop, safely limited speed, and safe direction. These functions require appropriate architecture, validation, testing, and documentation.

Standards and regulations vary by jurisdiction and application. Engineers should consult applicable machinery, functional-safety, electromagnetic-compatibility, elevator, industrial-control, and vehicle standards rather than assuming that a general-purpose drive is automatically compliant. Lockout/tagout, discharge-time verification, guarding, risk assessment, and cybersecurity controls are essential.

6. A Structured Selection Procedure

A defensible selection process can be organised as follows:

1. Define the mission profile: speed, torque, position, cycle time, starts per hour, ambient conditions, and operating modes.
2. Model the load: include friction, gravity, inertia, transmission efficiency, shock, and regeneration.
3. Determine continuous and peak requirements: calculate torque, power, acceleration, thermal duty, and braking energy.
4. Choose the motor family: compare induction, permanent-magnet, reluctance, or brushed machines.
5. Choose converter and feedback: check voltage, current, overload, control bandwidth, feedback resolution, braking, and communication.
6. Check mechanical integration: shaft, bearings, coupling, gearbox, alignment, torsional resonance, and mounting.
7. Evaluate environment: temperature, altitude, dust, water, corrosive agents, vibration, hazardous location, and enclosure rating.
8. Design protection and safety: fuses, disconnects, grounding, overloads, thermal sensors, safe stop, and emergency systems.
9. Evaluate energy and lifecycle cost: include losses, harmonics, downtime, maintenance, and replacement.
10. Validate: perform simulation, factory tests, site acceptance tests, parameter backups, and commissioning checks.

A weighted decision matrix can compare alternatives. Each criterion is assigned a weight w_j whose sum is one, and each alternative receives a normalised score s_ij. The weighted score is

This method structures judgement but does not eliminate engineering responsibility. A low score in a mandatory safety criterion cannot necessarily be compensated by a high score in cost.

7. Applied Case: Conveyor Retrofit

Background

This illustrative case concerns a 30 m packaging conveyor driven by a 7.5 kW induction motor through a gearbox. The existing direct-on-line starter causes mechanical shock, high starting current, and product instability. The conveyor operates 16 hours per day, five days per week, and requires two operating speeds: 0.8 m/s for normal production and 0.4 m/s during inspection.

Problem

The conveyor must start smoothly with a maximum loaded belt torque of 95 N·m at the gearbox output. The gearbox ratio is 10:1, motor speed during operation is 1,450 r/min, and gearbox efficiency is 92%. The required motor torque, neglecting acceleration torque initially, is

At 1,450 r/min, the corresponding motor power is

The installed 7.5 kW motor is therefore substantially oversized for the stated running load, although acceleration, jam clearance, thermal conditions, and future production must be checked before downsizing.

Analysis and approach

A variable-frequency drive with sensorless vector control is proposed. It provides controlled acceleration, two speed references, overload protection, and diagnostic data. The motor is not immediately replaced because the existing motor may be useful for standardisation and intermittent overload capacity. A measurement campaign records current, speed, start time, belt loading, and temperature over representative shifts.

The drive is selected with a motor-duty overload rating suitable for conveyor service, input protection, an EMC-compliant installation, and a braking resistor only if stopping time and stored kinetic energy require it. A mechanical emergency-stop circuit and safe torque off are included; software ramp-down is not treated as an emergency stop.

Outcome

The retrofit reduces starting shock and allows inspection speed without mechanical changes. If measured operation confirms that the motor remains lightly loaded, a later replacement with a correctly sized motor may reduce losses, but only after verifying cooling, overload margin, and standardisation costs. The decision demonstrates why nameplate power, rather than measured duty and load modelling, should not be the sole selection criterion.

Learning points

• Torque must be referred through the transmission correctly.
• Gearbox efficiency affects both required motor torque and power.
• A drive solves control problems but does not correct an unsuitable mechanical design.
• Safety functions must be independent and validated.
• Measurement before replacement can prevent both oversizing and undersizing.

8. Contemporary Developments and Limitations

Wide-bandgap silicon-carbide and gallium-nitride switches can reduce switching losses and increase power density, but they may create faster voltage transitions, common-mode currents, bearing-current risk, and greater insulation stress. Output filters, appropriate cable selection, grounding, and motor compatibility may be required.

Digital twins and model-based commissioning can estimate thermal state, predict faults, and test control strategies before installation. Artificial intelligence can assist anomaly detection using current, vibration, and temperature data. However, AI systems require representative data, validated thresholds, cybersecurity protection, and human oversight. A statistically detected anomaly is not by itself proof of a mechanical failure.

Cloud-connected drives improve fleet visibility but introduce authentication, software-update, data-governance, and availability concerns. Engineers should apply least-privilege access, network segmentation, secure backups, and controlled change management.

Common technical limitations include incomplete load data, uncertain duty cycles, catalogue ratings based on ideal cooling, poor grounding, incorrect encoder installation, unmodelled regeneration, and excessive reliance on default drive parameters. Good engineering combines calculation, manufacturer data, measurement, testing, and operational feedback.

Best-Practice Checklist

Before approving a drive design, confirm that:

• the complete load profile is known;
• continuous, peak, and regenerative conditions are covered;
• motor and converter ratings match voltage, current, overload, and cooling conditions;
• feedback resolution and control bandwidth meet the application;
• braking energy has a defined destination;
• harmonics, EMC, bearing currents, and cable effects are addressed;
• mechanical resonance and transmission backlash are considered;
• safety functions are risk-assessed, validated, and documented;
• maintenance access, spares, diagnostics, and training are available;
• lifecycle cost includes energy, downtime, and disposal;
• commissioning records and parameter backups are retained.

Chapter Summary

Drive selection is a system-engineering decision involving the motor, converter, controller, feedback, transmission, load, safety system, and operating environment. Load classification begins with torque–speed behaviour, inertia, acceleration, regeneration, and duty cycle. Induction motors are robust and economical; permanent-magnet and reluctance machines offer high efficiency or torque density; servo systems provide the feedback and control performance required for precision motion.

Robotics and CNC machines prioritise dynamic response and positioning. Pumps and fans benefit from variable-speed control because their power demand can vary approximately with the cube of speed. Conveyors and elevators require high starting or holding torque, while elevators and renewable systems demand carefully engineered regeneration. Electric vehicles combine traction performance, efficiency, battery limitations, thermal management, and functional safety.

A sound decision evaluates performance, efficiency, reliability, maintainability, safety, power quality, environmental conditions, and lifecycle cost. Weighted matrices, present-value analysis, load measurements, simulation, and commissioning tests support—but do not replace—engineering judgement. Contemporary drives increasingly use wide-bandgap power devices, network connectivity, digital twins, and AI-assisted monitoring, all of which introduce new integration and cybersecurity responsibilities.

Key Terms

Electrical drive: Integrated system that controls electromechanical energy conversion.

Torque–speed characteristic: Relationship between required or produced torque and rotational speed.

Duty cycle: Time sequence describing load, speed, and operating states.

Variable-torque load: Load whose torque typically increases with the square of speed.

Constant-power region: Operating region in which power remains approximately constant while torque decreases with speed.

Regeneration: Conversion of mechanical energy back into electrical energy.

Inertia reflection: Transformation of load inertia to the motor shaft through a transmission ratio.

Vector control: Converter control method that regulates flux- and torque-producing current components.

Servo drive: Closed-loop drive for accurate speed, torque, or position control.

Field weakening: Control operation that extends speed beyond base speed by reducing effective air-gap flux.

Safe torque off: Safety function that prevents the motor from producing torque without necessarily isolating all electrical voltage.

Lifecycle cost: Total discounted cost of ownership over the analysis period.

Power quality: Characteristics of electrical supply and distortion affecting equipment operation.

Braking resistor: Resistor that dissipates regenerated electrical energy as heat.

Sensorless control: Drive control that estimates motor state without a mechanical speed or position sensor.

Thermal equivalent torque: Approximate torque used to assess heating over a variable duty cycle.

Maximum power point tracking: Control that extracts maximum available power from a renewable source.

Common-mode voltage: Voltage component shared by conductors relative to ground, potentially causing bearing currents and EMC problems.

Review Questions

Short Answer Questions

1. Why is motor nameplate power alone insufficient for drive selection?
2. State the approximate torque–speed relationships for constant-torque, variable-torque, and constant-power loads.
3. What is the purpose of feedback in a servo drive?
4. Why can a centrifugal pump save substantial energy when operated at reduced speed?
5. Identify two conditions that can cause regenerative operation.

Long Answer Questions

1. Explain a complete drive-selection procedure from load definition through commissioning.
2. Compare induction, permanent-magnet synchronous, and synchronous-reluctance motors for industrial applications.
3. Discuss the special performance and safety requirements of elevator drives.
4. Explain how efficiency, reliability, maintainability, and lifecycle cost should be evaluated together.
5. Describe the principal drive requirements of an electric vehicle traction system.

Analytical / Application Questions

1. A conveyor requires 120 N·m at the load shaft and uses a 12:1 gearbox with 90% efficiency. Determine the motor torque required, neglecting acceleration torque. Explain what additional information is needed before selecting the motor.
2. A fan operates at 80% of rated speed. Using the affinity laws, estimate its relative shaft-power demand and state the assumptions behind the estimate.
3. Select between a simple scalar-controlled drive and a closed-loop vector servo for a vertical robotic axis. Justify the decision using torque, holding, positioning, safety, and maintenance criteria.

Multiple Choice Questions with Answers

Question 1

Which load is most closely associated with torque proportional to the square of speed?

A. Centrifugal fan

B. Loaded hoist

C. Constant-power spindle

D. Positive-displacement pump

Correct Answer: A. Centrifugal fan

Question 2

For an ideal gearbox with speed ratio i = ω_m/ω_L, the load inertia referred to the motor is:

A. J_L i^2

B. J_L/i^2

C. J_L/i

D. J_L + i^2

Correct Answer: B. J_L/i^2

Question 3

Which application most directly requires four-quadrant operation?

A. Constant-speed lighting fan

B. Elevator with lifting and lowering loads

C. Resistive heater

D. Unidirectional low-power blower

Correct Answer: B. Elevator with lifting and lowering loads

Question 4

The approximate shaft-power relationship for a centrifugal fan under similar operating conditions is:

A. P ∝ n

B. P ∝ n^2

C. P ∝ n^3

D. P ∝ 1/n

Correct Answer: C. P ∝ n^3

Question 5

What is the principal advantage of encoder feedback in a precision servo axis?

A. It eliminates all mechanical friction

B. It provides measured position or speed for closed-loop control

C. It removes the need for a power converter

D. It guarantees zero maintenance

Correct Answer: B. It provides measured position or speed for closed-loop control

Question 6

A motor produces 20 N·m at 1,500 r/min. Its approximate mechanical power is:

A. 0.31 kW

B. 3.14 kW

C. 31.4 kW

D. 300 kW

Correct Answer: B. 3.14 kW

Question 7

Which item is normally required when regenerated energy raises the DC-link voltage?

A. A braking resistor or regenerative energy path

B. A larger encoder only

C. A lower insulation rating

D. Removal of all current sensors

Correct Answer: A. A braking resistor or regenerative energy path

Question 8

Why may an oversized motor be undesirable?

A. It always has zero starting torque

B. It can operate inefficiently at light load and increase cost

C. It cannot be protected thermally

D. It prevents all speed control

Correct Answer: B. It can operate inefficiently at light load and increase cost

Question 9

Which criterion belongs directly in lifecycle-cost analysis?

A. Only catalogue purchase price

B. Energy, maintenance, downtime, and replacement costs

C. Only motor colour and enclosure shape

D. Only maximum no-load speed

Correct Answer: B. Energy, maintenance, downtime, and replacement costs

Question 10

Safe torque off is best described as a function that:

A. Provides mechanical braking in every condition

B. Prevents the motor from producing torque through the drive

C. Increases motor speed during an emergency

D. Replaces risk assessment and guarding

Correct Answer: B. Prevents the motor from producing torque through the drive