The Code Letter on a motor nameplate is used for what purpose?

The Code Letter on a motor nameplate is used for what purpose?

• A. Locked rotor kVA/hp (for starting current calculation)
• B. Maximum efficiency rating
• C. Number of poles
• D. Frame size

Answer: (C)

The code letter on a motor nameplate is used to identify the number of poles. The pole count determines the motor’s speed at a given line frequency (synchronous speed = 120 × frequency / number of poles). So, this code provides a quick way to know the motor’s speed characteristic without reading the mechanical drawing. For example, at 60 Hz a 2-pole motor runs about 3600 rpm, a 4-pole motor about 1800 rpm, and a 6-pole motor about 1200 rpm. Other items on the nameplate relate to different data (starting current and FLA for protective calculations, efficiency rating, or physical frame size), but the code letter itself is specifically tied to the pole count and the resulting speed.

The code letter on a motor nameplate is used to identify the number of poles. The pole count determines the motor’s speed at a given line frequency (synchronous speed = 120 × frequency / number of poles). So, this code provides a quick way to know the motor’s speed characteristic without reading the mechanical drawing. For example, at 60 Hz a 2-pole motor runs about 3600 rpm, a 4-pole motor about 1800 rpm, and a 6-pole motor about 1200 rpm.

Other items on the nameplate relate to different data (starting current and FLA for protective calculations, efficiency rating, or physical frame size), but the code letter itself is specifically tied to the pole count and the resulting speed.