1 April 2005

ISA Certified Automation Professional (CAP) Program

This question is from the CAP study guide, Domain II.

Definition: Identify customer requirements and complete high-level analysis of the best way to meet those requirements.

CAP question

What is the recommended limitation in meters for the length of a fast Ethernet (100 Megabits per second) segment on twisted pair cable?

A. 10

B. 100

C. 300

D. 350

CAP answer

The correct answer is B, 100 meters.

Because of the high speed of fast Ethernet, the use of twisted pair cable is limited to 100 meters (328 feet). Ten meters would limit installations unnecessarily. Three hundred meters and 350 meters would exceed recommendations substantially, resulting, potentially, in signal errors.

Reference: Berge. Fieldbuses for Process Control: Engineering, Operation, and Maintenance, ISA Press, 2001.

Nicholas Sheble (nsheble@isa.org) edits the Certification department. For information about the CAP program, go to www.isa.org/CAP.