Polarity is very important to know when banking and ______ transformers.

• A. Paralleling
• B. Step-up
• C. Autotransformer
• D. Isolation

Answer: (A)

When connecting multiple transformers to share load, you must make sure their voltages are in phase so their magnetic fields reinforce each other. Polarity, shown by the dot marks on windings, tells you which ends of the windings are in the same phase at any moment. If you connect transformers with opposite polarity, they can oppose each other, driving circulating currents between the units, causing overheating, protection trips, and uneven load sharing. Ensuring identical polarity across all transformers in a bank lets the voltages add properly and the bank behave as a single, larger source.

While polarity matters for all transformers, the idea highlighted here specifically applies to paralleling or banking transformers, where improper polarity would create a direct conflict between sources. The other options describe different transformer types or purposes and aren’t about the essential requirement for correct phasing when transformers are tied together in parallel.