What power ratings are available for metal clad resistors?

Metal clad resistors typically range from 10W to 50W (compact designs), 50W to 150W (standard chassis mount), and 150W to 500W or more for high-power applications. Higher ratings are possible with proper heat sinking.

Tech Talk
Metal Clad Resistors: Construction, Applications,
and High-Power Performance Guide

Q: What are metal clad resistors used for?

Metal clad resistors are commonly used in motor braking systems (dynamic braking), load banks and power testing equipment, power supplies and inverters, industrial automation systems, and electric vehicles and charging systems. They are ideal for absorbing and dissipating large amounts of electrical energy safely.

Q: Do metal clad resistors require cooling?

Yes, proper cooling is essential. Without adequate heat dissipation, the resistor must be derated. Mounting to a heat sink or metal chassis is strongly recommended.

Q: What industries use metal clad resistors?

Metal clad resistors are widely used in industrial automation, renewable energy (solar, wind), automotive and EV systems, and power electronics and energy storage.

Metal clad resistors are among the most reliable and versatile components used in modern power electronics. Known for their durability, heat dissipation, and high power handling, these resistors are widely used in industrial, automotive, and renewable energy systems.

In this guide, we’ll explore how metal clad resistors are built, where they are used, and why they are essential in demanding electrical applications.

What Are Metal Clad Resistors?

Metal clad resistors (also called aluminum-housed or wirewound power resistors) are high-power resistors enclosed in a rugged metal casing—typically aluminum.

They are designed to dissipate large amounts of heat efficiently while maintaining stable electrical performance.

RARA’s metal clad resistor range includes models such as:

RH10C (10W cement encased)

RH / FRH (15W–50W aluminum housed)

URH (20W–100W UL-rated)

Image of the IRN ULN ITF ULF metal clad resistor

IRN / ULN / IRF / ULF (50W–500W high power)

Image of the ARN automotive resistor AECQ200

Automotive-grade ARN series (up to 150W)

These products cover a wide range of resistance values, tolerances, and thermal characteristics.

Construction of Metal Clad Resistors

Metal clad resistors are typically wirewound resistors inside an aluminum enclosure, optimized for thermal management.

Key Construction Elements

1. Resistive Element (Wirewound Core)

Made from alloys such as nichrome or similar resistive wire
Wound around a ceramic core for insulation and thermal stability
Provides precise resistance and excellent stability under load

Wirewound designs are known for:
High accuracy
Low noise
Strong overload capability

2. Ceramic Insulation Core

Electrically isolates the resistive wire
Provides mechanical strength and heat resistance

3. Heat-Resistant Cement Filling

Encapsulates the wire element
Protects against vibration, dust, and mechanical stress
Improves thermal conduction to the outer casing
This construction makes the resistor resistant to harsh environments

4. Aluminum Housing (Metal Cladding)

Acts as a heat sink
Allows mounting directly to chassis or external heat sinks
Enables high power ratings (often up to hundreds or even thousands of watts)

5. Terminals / Connections

Screw terminals, leads, or busbars
Designed for high-current connections and easy installation

Key Features and Advantages

1. Excellent Heat Dissipation

The aluminum casing efficiently transfers heat away from the resistive element, allowing continuous operation at high power.

2. High Power Ratings

Metal clad resistors commonly operate from:
10W to 500W (standard)
Up to 1000W+ with proper heat sinking

3. Mechanical Durability

Resistant to vibration and shock
Suitable for industrial and automotive environments

4. Wide Resistance Range

Typical ranges include:
0.1Ω to several MΩ depending on model

5. Stability and Reliability

Low temperature coefficient (TCR)
Stable performance across wide temperature ranges

Applications of Metal Clad Resistors

Metal clad resistors are used wherever high power dissipation and reliability are required.

1. Motor Drives & Dynamic Braking

Used as braking resistors in VFD systems
Absorb excess energy when motors decelerate
Prevent damage to drive electronics

These are commonly used in:

Elevators
CNC machines
Industrial automation systems

2. Power Supplies & Inverters

Pre-charge and discharge circuits
Energy dumping in power electronics
Voltage balancing
Applications include:
Solar inverters
UPS systems
EV charging infrastructure

3. Load Banks & Testing Equipment

Simulate electrical loads for testing generators and power systems

Used in:

Data center testing
Generator commissioning
Battery discharge systems

4. Industrial Machinery

Current limiting
Snubber circuits
Heating and energy dissipation
Widely used in:
Manufacturing equipment
Robotics
Automated control systems

5. Automotive & EV Systems

Electric vehicle charging and braking
Battery management systems
High-power resistive loads
RARA’s AEC-Q200 automotive series reflects this growing demand

Example Product Configurations

Low Power (10W–50W)

Compact aluminum or cement-encased designs
Used in control circuits and smaller systems

Medium Power (50W–150W)

Chassis-mounted resistors
Used in industrial control and automation

High Power (150W–500W+)

Heavy-duty aluminum housings
Often mounted to heat sinks
Used in braking, load banks, and energy dissipation systems

Inductive vs Non-Inductive Designs

Metal clad resistors can be configured as:

Inductive (Standard Wirewound)

Higher power capability
Suitable for DC or low-frequency applications

Non-Inductive

Special winding techniques cancel inductance

Used in:

High-frequency circuits
Pulse applications
Snubber networks

Thermal Management Considerations

To maximize performance:

Mount resistors on metal surfaces or heat sinks
Use thermal compound if required
Ensure proper airflow
Without proper heat dissipation, power ratings must be derated.

Why Choose Metal Clad Resistors?

Metal clad resistors are the go-to solution for high-power, high-reliability applications because they offer:

Superior heat handling
Long operational life
Mechanical robustness
Flexible configurations
Broad application range
As industries shift toward electrification (EVs, renewable energy, automation), demand for these resistors continues to grow.

Conclusion

Metal clad resistors are a critical component in modern power electronics, combining rugged construction with high-performance electrical characteristics. From motor braking systems to renewable energy applications, their ability to safely dissipate energy makes them indispensable.

Manufacturers like RARA provide a wide range of configurations—from compact 10W units to high-power 500W+ chassis-mounted resistors—ensuring solutions for virtually any application.

Frequently Asked Questions About Metal Clad Resistors

What is a metal clad resistor?

A metal clad resistor is a high-power resistor enclosed in an aluminum housing designed for efficient heat dissipation. These resistors are typically wirewound and are used in applications requiring high reliability and power handling.

What are metal clad resistors used for?

Metal clad resistors are commonly used in:
Motor braking systems (dynamic braking)
Load banks and power testing equipment
Power supplies and inverters
Industrial automation systems
Electric vehicles and charging systems
They are ideal for absorbing and dissipating large amounts of electrical energy safely.

How do you mount a metal clad resistor?

Metal clad resistors should be mounted to a metal surface or heat sink to maximize heat dissipation. Using thermal compound between the resistor and mounting surface improves thermal conductivity and performance.

What is the difference between wirewound and metal clad resistors?

Wirewound refers to the internal construction (resistance wire wound around a core), while metal clad refers to the external aluminum housing. Most metal clad resistors use wirewound elements inside.

Are metal clad resistors inductive?

Standard metal clad resistors are inductive due to their wirewound design. However, non-inductive versions are available using special winding techniques for high-frequency or pulse applications.

What power ratings are available?

Metal clad resistors typically range from:
10W to 50W (compact designs)
50W to 150W (standard chassis mount)
150W to 500W+ (high-power applications)
Higher ratings are possible with proper heat sinking.

Do metal clad resistors require cooling?

Yes. Proper cooling is essential. Without adequate heat dissipation, the resistor must be derated. Mounting to a heat sink or metal chassis is strongly recommended.

What industries use metal clad resistors?

These resistors are widely used in:
Industrial automation
Renewable energy (solar, wind)
Automotive and EV systems
Power electronics and energy storage

Tech TalkMetal Clad Resistors: Construction, Applications, and High-Power Performance Guide