The motor enclosure used for industrial purposes is

Question

Examoogle · Accepted Answer

Protected type

Explanation: A protected type motor is designed with an enclosure that provides a degree of protection against accidental contact with live or moving parts while allowing adequate ventilation. It is the standard choice for most indoor industrial environments where the atmosphere is relatively clean and dry.

Working Principle: The enclosure utilizes strategically placed openings or mesh guards. These openings are sized to prevent external objects (such as tools or fingers) from touching rotating parts, while facilitating the flow of cooling air through the motor frame to maintain thermal equilibrium under steady-state load conditions.

Key Formulas: $T \propto \Phi \cdot I_a$ — torque developed is proportional to flux and armature current; $P_{loss} = I^2R + W_c$ — power loss due to heating requiring ventilation

Key Points: Protected enclosures ensure safety by restricting access to hazardous internal parts.; They are not hermetically sealed and rely on ambient air for cooling.; Not suitable for outdoor use or environments with heavy dust/moisture.; Industrial standards are governed by IP ratings (typically IP21/IP22).

Advantages: Cost-effective for standard factory floors; Excellent heat dissipation due to direct air flow; Easy to maintain and inspect

Disadvantages: Vulnerable to water dripping or splashing; Not suitable for corrosive or hazardous chemical environments; Limited protection against fine particulate dust

Applications: General purpose indoor machinery; Conveyor systems; Machine tools in clean shops

Additional Info: Drip-proof motors are a subset of protected motors designed specifically to prevent entry of falling drops of liquid.. Totally enclosed motors are used when environmental contamination is severe, but they require larger frames for the same power rating due to limited convective cooling.

Answer: A is correct — The protected type enclosure is the standard industrial choice providing the necessary balance between worker safety and efficient motor cooling.

Exam Tip: Always relate motor enclosures to their specific IP rating; an IP21 motor is protected against solid objects > 12mm and vertical water drops, whereas an IP54 motor is required for dust and splash resistance.

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