February 2009
ISA Certified Automation Professional (CAP) program
Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems.
The following question comes from the CAP study guide, Performance Domain III, System Design, Design, specify, and procure the hardware/software used in the system
CAP question
To minimize electrical interference when AC power and DC signal wiring meet in a control panel, it is BEST to:
A. Use a different size wire.
B. Cross the wires at 90 degrees.
C. Run the wires parallel to each other.
D. Twist the AC wires around the DC wires.
CAP answer
The correct answer is B, cross the wires at 90 degrees.
Crossing the wires at 90 degrees will minimize the exposure of the wires to each other and therefore minimize the effects of interface. “Using a different size wire” will have no effect on the electrical interference. “Running the wires parallel to each other” will increase the exposure of the wires to each other and increase the effects of interference. “Twisting the AC wires around the DC wires” will also increase the effects of interference.
Reference: Thomas A. Hughes; Programmable Controllers, 4th Edition; ISA Press, 2005
Read questions answered by our experts or join the email list.
