As shown in figure "B" of the illustration of the motors of the solidly grounded distribution system, assuming all three motors are running, what statement is true if the following current readings are taken with an AC clamp-on ammeter clamped around the entire cable rather than individual conductors of a cable? Common loop: 3 amps Motor #1 loop: 0 amps Motor #2 loop: 3 amps Motor #3 loop: 0 amps See illustration EL-0128.
• How a clamp-on ammeter behaves when it is clamped around all conductors of a 3‑phase motor circuit instead of a single conductor • In a solidly grounded system, how ground-fault current returns to the source through equipment grounding conductors and bonding jumpers • How the common loop reading relates to the sum of all ground-fault currents, and how each motor loop isolates which motor’s grounding path is carrying fault current
• If the clamp encircles all three phase conductors to a healthy motor (no ground fault), what is the net magnetic field / net current the meter sees, and why? • If one motor has a ground fault to its frame, which physical path will the fault current take back to the source in this diagram, and which loop(s) will now show a non‑zero reading? • Compare the given readings: which motor’s loop shows current, and what does that specifically say about where the ground-fault current is flowing?
• Remember that for a balanced 3‑phase load with no ground fault, the vector sum of the three phase currents is zero, so a clamp around all three should read ~0 A • Verify which conductors pass through each labeled loop in figure B (common loop vs motor #1, #2, #3 loops) and which of those include the equipment grounding/bonding jumper • Match each choice to the idea: “grounded motor” = loop shows ground-fault current, “free of grounds” = loop reads ~0 A; then see which option fits all four meter readings simultaneously
No comments yet
Be the first to share your thoughts!