What should the multimeter read between the two windings of a transformer?

• A. OL
• B. 0
• C. 1
• D. 10

Answer: (A)

The key idea is that transformer windings are electrically isolated from each other, connected only through magnetic coupling. When you measure DC resistance between the primary and secondary with a multimeter, there is no direct conductive path, so the reading appears as infinite resistance. Multimeters often display this as OL (open loop). This shows there’s proper insulation between windings and no shorted path. If you did see a finite low resistance, that would indicate a fault such as a shorted turn or compromised insulation. Remember, you’d typically measure the resistance of each winding individually to verify they’re intact, and then expect an open circuit between windings.