The post AutoQuiz: How Do You Avoid a Ground Loop on Shielded Cable? first appeared on the ISA Interchange blog site.
Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for information about the CCST program. This question comes from the Level I study guide, Domain 3, Troubleshooting. Level I represents a professional who has a five-year total of education, training, and/or experience.
A ground loop on shielded cable can be avoided by:
a) attaching a safety ground to the instrument casing
b) grounding the shield at only one end of the circuit
c) attaching a safety ground to the control panel
d) grounding the shield at both ends of the cable
e) none of the above
A ground loop refers to an unwanted electrical current in a conductor connecting two points that are supposed to be at the same potential (units are volts), but that are actually at different potentials (not grounded). Ground loops are detrimental to the intended operation of the electrical system.
Potential is the difference in voltage between two points. One of the points should be a ground with voltage equal to 0 (zero).
The best way to avert the ground loop in this question is to ground the shield at only one end of the circuit.
The correct answer is B.
Source: ISA News