# AutoQuiz: How to Calculate the Speed of a Four-Pole Synchronous Motor

AutoQuiz is edited by Joel Don, ISA’s social media community manager.

Today’s automation industry quiz question comes from the ISA Certified Automation Professional certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional’s skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for information about the CAP program. The following question comes from the CAP study guide, Performance Domain V, Deployment.

Considering a 60 Hz power source, at what speed does a four-pole synchronous motor run?

a) 1200 RPM
b) 1800 RPM
c) 2400 RPM
d) 3600 RPM
e) none of the above

Synchronous speed in RPM = (two × frequency × 60) / (number of poles). For a 60 Hz, four pole motor that would be = (two × 60 × 60) / four = 1800

The correct answer is B, 1800 revolutions per minute (RPM).

Reference: Webb, Industrial Control Electronics, Merrill Publishing, 1990

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