A low voltage, high current testing unit...

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Question 1 of 2066636eed28f7522a1c51d75f

A low voltage, high current testing unit consisting of an autotransformer, ammeter, and timer may be used to test the proper tripping function of a three-pole magnetic circuit breaker. What is the correct procedure for using this apparatus?

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Question 1 of 20

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🔍 Key Concepts

• Common tripping bar purpose on a three‑pole magnetic circuit breaker • Difference between testing each pole individually vs all poles simultaneously • How a clamp‑on ammeter reads current when clamped around one conductor vs multiple conductors

💭 Think About

• Ask yourself what you are trying to prove when testing the tripping function of a three‑pole breaker: is it the individual pole performance, the common trip mechanism, or both? • Think about what happens to the net magnetic field (and indicated current) in a clamp‑on ammeter if it encircles all three phase conductors carrying balanced three‑phase current. • Consider whether the common tripping bar should stay connected or be removed if you want to verify that one overloaded phase will trip all three poles together.

✅ Before You Answer

• Verify how a clamp‑on ammeter behaves if it is clamped around all three phase conductors of a balanced three‑phase circuit (what current will it show?). • Check the intended function of the common tripping bar on a three‑pole breaker: does it need to be attached or removed to confirm that an overcurrent in one pole trips all three? • Confirm whether testing procedures for three‑pole breakers typically require testing each pole separately or all poles at once to get meaningful time‑current data.

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