Carbon Brushes: What They Do and When to Replace Them

carbon brushes maintenance for electric motors brushes for electric motors carbon brushes for electric motors

Carbon brushes, also called motor brushes, are an essential part of many electric motors. Used across all kinds of industrial and commercial equipment, these small components keep electricity flowing between a motor’s stator windings and the rotating center of the motor.

Understanding carbon brushes helps you prevent motor damage and avoid costly downtime. That’s why we’ve compiled the internet’s top-searched questions about motor brushes into one simple guide.

In this guide, you'll learn:

• What carbon brushes do

• How to tell when brushes are wearing out

• What causes sparking and how to prevent damage

• How to replace brushes safely and correctly

What are brushes in a motor & what are their purpose?

Motor brushes are small sliding blocks, usually made of carbon, that create a continuous electrical pathway between the stationary wires of a motor and its spinning center. They do this by “brushing” against the rotating part of the motor, acting as a sliding contact.

Quick note: In motors and generators that use brushes, the rotating surface the brush rides on is usually either a commutator or slip rings (also called collector rings). Commutators are made of segmented copper bars and are designed to switch/reverse current as the motor turns. These are most commonly used in brushed DC motors and universal motors. Slip rings are smooth continuous rings that provide a continuous electrical connection to a rotating assembly (no mechanical switching). You’ll most often see slip rings in wound-rotor AC induction motors and in some generator/excitation setups.

Because brushes are designed to constantly rub against moving parts, they’re the primary wear point of the motor, sacrificing themselves to help protect more expensive internal rotating assemblies.

Are carbon brushes universal?

Short answer: no, carbon brushes are not universal. While they might look similar, the details make all the difference when it comes to performance and motor life.

Carbon brushes are designed for specific motors, taking into account things like voltage, current, RPM, temperature, and load. Even a small change in brush composition or size can cause problems like poor contact, excess arcing, uneven wear, and accelerated commutator damage.

Every electric motor has specific needs when it comes to brush material and design. Some brushes are softer and designed to wear faster to protect the commutator, while others are harder for heavy-duty industrial use.

When it’s time to replace your brushes, always match the size, material grade, and style to the original specifications. If you’re not sure what your motor needs, check the markings on the old brush or the motor’s nameplate. Feel free to reach out to our team at sales@esrmotors.com for help with this process.

What are the pros and cons of carbon brushes?

When it comes to electric motors, brushed motors (motors that use carbon brushes) aren’t your only choice. Brushless motors are another option that manage power transfer electronically, not mechanically like brushed motors.

Because brushless motors don’t use consumable carbon brushes that naturally wear over time, they typically have lower maintenance requirements and are, generally, more efficient.

However, brushed motors still have several advantages that make people choose them:

• Cost-effectiveness: Because they use mechanical commutation (brushes) rather than complex electronic controllers, brushed motors are often cheaper to purchase up front.
• Simple control systems: Unlike brushless motors that require an electronic drive to operate, a brushed motor can often be connected directly to a DC power source. This simplicity can make them easier to integrate and troubleshoot in many legacy industrial environments.
• High torque at low speeds: Brushed DC motors are known for strong low-speed torque, which is why you still see them used in cranes, winches, and heavy traction applications.
• Durability in harsh environments: Because they lack sensitive onboard electronics, brushed motors can often handle extreme temperatures and rugged conditions better than their brushless counterparts.

How often should motor brushes be replaced?

Depending on how the motor is being used, carbon brushes often last anywhere from 1,000 to 4,000 hours but real-world brush life can vary a lot based on load, heat, dust, humidity, and commutator condition.

According to Helwig Carbon, brushes should be replaced at signs of cracking, disintegrating, or burning.

A practical rule of thumb: all brushes have a minimum length and if they’re worn to (or near) that point, it’s time to replace.

How do I know if my carbon brushes are bad?

Common signs of brush trouble include:

Excessive or worsening sparking
Loss of power / inconsistent speed
Visible burning, chipping, cracking, or crumbling
Uneven wear (one brush much shorter than others)
Heavy carbon dust buildup inside the motor or brush holder area
Noise changes (a new “scratchy” sound can mean poor contact)

Important note: Some light “pinpoint” sparking can be normal in brushed motors. What you don’t want is bright, sustained arcing, heavy sparking, or a sudden change in sparking behavior.

Can worn brushes damage a motor?

Yes. Worn carbon brushes can damage a motor if left unchecked and can potentially lead to motor failure.

When brushes get too worn, it can lead to:

Loss of electrical contact
Brushes need consistent contact to properly carry current. Poor contact can cause unstable commutation and other issues.
Excessive sparking / arcing
Light sparking can be non-destructive, but destructive sparking can electrically erode both the brush and the commutator. If it’s not corrected, it can eventually lead to equipment failure.
Heat damage and accelerated wear
When sparking and commutation problems increase, heat typically increases too. Commutator overheating is tied to specific wear patterns (like “copper drag”), and once the surface starts overheating/softening, wear can snowball fast.
Commutator wear (grooves, burning, machining damage)
On motors with commutators, poor electrical contact can lead to arcing that essentially “machines” the commutator surface and causes grooving. In more severe cases, high sparking levels can remove metal from commutator bar edges (burning/etching that gets worse with continued operation).

An important note: the brush isn’t always the original culprit. Sparking at the brush face is often the first sign that something else needs attention (spring pressure, brush holder condition, commutator surface, alignment, load, contamination, etc.).

Also worth knowing: carbon brush dust is conductive. If it builds up inside a motor, it can cause tracking, shorts, and extra heat, so cleanliness matters.

Can I replace carbon brushes myself?

Yes, replacing carbon brushes is often something you can do yourself.

Keep in mind that carbon brushes are specific to the motor they’re in. Our team can help you locate exact replacements that will keep your operations running without delay. If you aren’t comfortable replacing them yourself, one of our experienced team members can help connect you with a repair shop that can.

Before you order replacements, check these basics:

• Brush size and lead/terminal style
• Brush grade/material (match OEM spec when possible)
• Brush holder condition (brush should slide freely)
• Spring condition/pressure
• Commutator or slip ring condition (grooves, burns, rough surface, out-of-round)
• Uneven wear patterns across brushes (replace as a set when appropriate)

How do I replace carbon brushes?

To replace carbon brushes, here are the steps you should follow, according to Helwig Carbon:

1. Disconnect power using approved lockout/tagout procedures.
2. Remove the old brushes and inspect them (take note of unusual conditions of the brush or brush holders).
3. Inspect the commutator for any unusual conditions. Check out this helpful commutator appearance guide.
4. Check the inside of the holder cavity for dust, dirt, carbon build-up, or burned areas. Clean if necessary.
5. Check the terminal connections. Clean if necessary.
6. Secure holders to the mount by checking for tightness and proper alignment.
7. Check the spring force of current springs and make sure they are within the recommended range.
8. If the replacement brushes are made from a different grade of material, remove any old film from the brush tracks using a dry untreated canvas or rubber abrasive.
9. Install new brushes into the holders, paying attention to the orientation of angle-holder designs.
10. Apply the constant-force spring. After applying the spring, pull up on the brush and release gently to make sure the brush moves freely in the holder.
11. Connect the terminals and make sure connections are tight and secure.
12. Seat the brush with commutator garnet paper. (Avoid emery cloth—conductive grit can cause problems.)
13. For final wear-in, operate the DC machine at no load.

Helwig Carbon makes a great video guide to replacing your brushes. Click the link to watch:
https://youtu.be/DM-PiNqYHC8

Final Thoughts

Carbon brushes are a small but essential part of brushed electric motors. A little inspection and maintenance can go a long way in preventing commutator damage and avoiding downtime.

To learn more, make sure to check out our further resources listed below or contact our team to get specific questions answered. The ESR team is here to help you with all your electric motor needs.