You've described a classic scenario for an ungrounded system. The high voltages you're measuring to ground are due to capacitive coupling. Here's a breakdown of why you're seeing this and why it's higher than you might expect: Capacitive Coupling to Ground

Every conductor has a small amount of capacitance to ground. This capacitance exists between the transformer windings and the grounded metal enclosure of the transformer, and between the secondary conductors and any grounded conductive objects near them (conduit, equipment frames, etc.). This capacitance forms a high impedance path to ground.

Floating Neutral & Voltage Division

Because the secondary is ungrounded (floating), the voltage isn't fixed relative to ground. The lines of the secondary are essentially capacitively "tied" to ground through these capacitances. Think of it like two capacitors in series from each line to ground, forming a voltage divider. The voltage from each line to ground depends on the ratio of these capacitances.

The High Voltage Explanation



Balanced Capacitance (Ideal Case - Rarely Seen)

If the capacitance from each secondary line to ground were perfectly equal, you'd expect to see roughly half the secondary voltage (60VAC) from each line to ground. This is what you'd expect theoretically.

Imbalanced Capacitance (What's Happening Here)

In reality, the capacitances are almost NEVER equal. Differences in wiring runs, proximity to grounded objects, and even the physical construction of the transformer itself will cause imbalances. When one side has much less capacitance to ground than the other, it will be pulled much closer to ground potential, while the other side will be pulled up higher in voltage relative to ground. The 460VAC and 401VAC readings indicate a significant imbalance in capacitive coupling.

Why 460VAC and 401VAC Exceed 120VAC? This is key. The ungrounded secondary allows the entire secondary circuit to float to a voltage above ground. The voltage difference between the two secondary lines will always be 120VAC (the transformer output), but the reference point of the circuit as a whole can shift significantly relative to ground potential. The imbalance in capacitive coupling allows one line to "float" above ground potential and the other line to "float" below ground potential, by much larger amounts. Why This Can Vary (and why you've seen lower voltages before)

The exact voltage levels to ground depend on:

The amount of capacitance to ground

Longer wire runs, more proximity to grounded objects, and even humidity can increase capacitance.

The balance of capacitance

Even small changes in wiring can significantly affect the balance.

Source Impedance

The source impedance of the primary power feeding the transformer affects how readily the voltage can be pulled away from the ideal.

Loads Connected

If there are loads connected, they can provide alternate, resistive paths to ground, which can bleed off some of the voltage.

Why This is a Problem (or not)



Nuisance Tripping (Less Common on such a Small Transformer)

The capacitive coupling can, in some cases, create enough current to trip ground fault protection, if there's a significant imbalance.

Increased Risk of Insulation Breakdown

Higher voltage stress on insulation can contribute to eventual failure, although with a 120V secondary, it's less of an immediate concern compared to higher voltage systems.

Confusing Troubleshooting

As you've experienced, these voltages can mislead troubleshooting efforts.

Not Necessarily a Critical Problem

Ungrounded systems can operate perfectly fine for many years. They often provide continuous operation even with a single ground fault (though the ground fault should be located and corrected promptly).

What to Do

1.

Confirm Ungrounded

Double-check that the neutral is truly ungrounded. It sounds like you already did this, but it's crucial. Look for any accidental connections to ground.2.

Document and Monitor

Record the voltages to ground on both lines. If the voltages are stable, and the system is operating correctly, you can choose to leave it alone. Monitor for changes.3.

Consider Grounding (with precautions)

The best solution is often to establish a grounded neutral on the secondary.

However, do NOT simply ground one side. You MUST do this through a grounding resistor. A resistor limits the ground fault current and prevents high fault currents that could damage equipment. Grounding Resistor

Use a properly sized grounding resistor. A common choice is to limit the ground fault current to around 5-10 amps. Consult with an electrical engineer or qualified electrician to determine the correct resistor value and wattage.

Proper Connection

Connect the grounding resistor between the "neutral" point of the secondary and the grounding system.

In summary, the voltages you're seeing are due to capacitive coupling in an ungrounded system, exacerbated by an imbalance in the capacitance to ground from each secondary line. While not necessarily immediately dangerous, this can be confusing and can indicate a potential issue with insulation stress. Grounding through a resistor is the best long-term solution, but should be done carefully by a qualified professional.Disclaimer: I am an AI chatbot and cannot provide electrical engineering advice. Consult with a qualified electrician or electrical engineer for any work on electrical systems. Working with electricity can be dangerous. Flag for review