After replacing a single-phase transformer, the voltage at the customer's panel is low. What should you check?

• A. Inspect all connections and service conductors for looseness or corrosion, verify the service-wire size, and adjust tap changer settings.
• B. Replace the transformer again.
• C. Ignore measurements and wait.
• D. Check the meter readings at the main panel.

Answer: (C)

When the voltage at the panel remains low after replacing a single-phase transformer, focus on the things that directly affect voltage delivery and regulation. The most common culprits are loose or corroded connections and service conductors. A bad lug, terminal, or splice adds resistance, which causes a voltage drop under load and leaves the panel with a lower voltage than expected. So, inspect every connection from the service head through the transformer, the disconnects, and the panel for looseness or corrosion, and tighten or replace as needed.

Also verify the service conductors are the correct size for the service and for the transformer’s rating. Undersized conductors can’t carry the current without excessive voltage drop, especially when customers draw significant load.

If the transformer has adjustable tap changers, check that they’re set to the correct position for the incoming line voltage and the desired secondary voltage. A mis-set tap can produce a lower-than-desired output at the panel.

Using voltage measurements to guide you helps—check both primary and secondary voltages to identify where the drop is occurring. Replacing the transformer again won’t fix these issues if the root cause is a bad connection, improper conductor sizing, or incorrect tap settings. Ignoring measurements and waiting isn’t a solution; diagnose with the readings and correct the underlying problem.