I recently had a situation with a low voltage landscape lighting transformer that is puzzling me. The transformer was connected to a GFCI, which was reading normally (~117 volts). In the transformer, there is an outlet designed to accept an accessory timer. When testing across this outlet, I received voltage readings of between 90 and 104 volts. However, the transformer would not operate. The GFCI did not trip.
Upon further investigation, I determined that the homeowner had unplugged the transformer under full load. This resulted in damage to the neutral on the power cord. A continuity check on the neutral confirmed that it had completely failed and that it was unable to conduct any electricity. Replacing the power cord fixed the problem.
I would appreciate it if someone can explain to me why I might have received a reading of 90-104 volts when testing on the outlet since, ordinarily, when you test between hot and ground, you receive the same reading as testing between hot and neutral.