If transformer primary is 120V and secondary is 12V at 20A, what is the primary current?

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Prepare for the CWEA Electrical/Instrumentation (E/I) Grade 1 Test. Use flashcards and multiple-choice questions, each with hints and explanations. Get ready for your exam!

Multiple Choice

If transformer primary is 120V and secondary is 12V at 20A, what is the primary current?

Explanation:
In an ideal transformer, power in equals power out (Vp × Ip = Vs × Is). The secondary side supplies 12 V at 20 A, which is 240 VA. To find the primary current, divide by the primary voltage: Ip = (Vs × Is) / Vp = 240 / 120 = 2 A. So the primary current is 2 amperes. This assumes ideal conditions; real transformers have small losses, but the current will be very close to 2 A.

In an ideal transformer, power in equals power out (Vp × Ip = Vs × Is). The secondary side supplies 12 V at 20 A, which is 240 VA. To find the primary current, divide by the primary voltage: Ip = (Vs × Is) / Vp = 240 / 120 = 2 A. So the primary current is 2 amperes. This assumes ideal conditions; real transformers have small losses, but the current will be very close to 2 A.

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