**Brushes and Commutating Poles in DC Motors**

In a DC motor, the commutator and brushes play a crucial role in the conversion of electrical energy to mechanical energy. The commutator is a rotating switch-like device that facilitates the flow of current through the motor windings. The brushes, typically made of carbon or graphite, make contact with the commutator and help in the transfer of current.

**Commutating Poles and Brush Lead**

Commutating poles, also known as interpole or compensating poles, are additional pole pieces that are placed between the main field poles of a DC motor. Their purpose is to improve the commutation process by reducing sparking and increasing the motor's overall performance.

The brushes in a DC motor are typically placed in a specific position with respect to the commutator segments. This positioning is known as the brush lead. The brush lead can be either forward or backward, depending on the motor's design and requirements.

**Backward Lead and No Commutating Poles**

When a DC motor does not have commutating poles, the brushes are given a backward lead. This means that the brushes are positioned slightly behind the neutral axis of the commutator segments.

The reason for providing a backward lead in such motors is to ensure smooth and efficient commutation. As the armature rotates, the brushes make contact with the commutator segments. In a motor without commutating poles, the brushes tend to drag the current in the opposite direction of armature rotation. This backward lead compensates for this effect.

**Advantages of Backward Lead**

- **Reduced Sparking:** By giving the brushes a backward lead, the likelihood of sparking between the brushes and commutator segments is significantly reduced. This is important because sparking can cause wear and tear, leading to decreased motor lifespan.

- **Improved Commutation:** The backward lead helps in achieving better commutation, which is the process of transferring the armature current from one commutator segment to the next. This ensures that the motor operates smoothly and efficiently.

- **Enhanced Motor Performance:** By reducing sparking and improving commutation, the backward lead contributes to overall motor performance. It helps in reducing electrical losses, improving power transfer efficiency, and maximizing the motor's torque and speed characteristics.

**Conclusion**

In a DC motor without commutating poles, the brushes are given a backward lead. This positioning helps in reducing sparking, improving commutation, and enhancing the motor's overall performance. The backward lead compensates for the drag effect of the brushes and ensures efficient conversion of electrical energy into mechanical energy.