You're right on track with your understanding of floating neutral inverters and the potential for phantom voltages. The fact that you received a shock, even a small one, needs investigation. You are also correct it could be capacitance. Let's break down the likely causes

Understanding the Situation
Floating Neutral

An ungrounded neutral system isn't directly connected to ground (the vehicle chassis in this case). This theoretically prevents ground loops and makes the system more tolerant of a single fault.

Phantom Voltages

High-impedance voltmeters can pick up stray voltages due to capacitive coupling and electromagnetic fields. These are usually harmless.

Low-Impedance Meters

Low-impedance meters "load down" the circuit, effectively shunting these phantom voltages to ground.

Your Observation

The crucial point is that you received a shock, indicating a real current flow, not just a phantom voltage reading.

Possible Causes of the Shock1. Capacitive Coupling (Most Likely)



Mechanism

The inverter's internal components (transformer windings, heatsinks, etc.) have capacitance to the inverter's metal case, and the case is electrically connected to the chassis of the truck. The AC voltage on the hot (phase) conductor capacitively couples to the chassis. This forms a very high-impedance path, but still allows a small AC current to flow when you touch the hot conductor and the chassis simultaneously.

Factors Increasing Capacitive Coupling

Higher AC frequency (most inverters output modified sine waves, which have higher frequency components). Larger surface area of internal components. Closer proximity of internal components to the case.

Why it's surprising

The current is small, but even a small current at 60VAC can be perceptible, especially if your skin is damp or you have a low tolerance to electrical shock.2.

Leakage Current through Insulation



Mechanism

Imperfect insulation within the inverter can allow a small leakage current to flow from the AC circuits to the case. Over time, insulation can degrade due to heat, vibration, or contamination (dirt, moisture).

Likelihood

Less likely than capacitive coupling if the inverter is new and well-maintained.3.

DC Leakage (If Inverter has DC Isolation)



Mechanism

Some inverters have DC isolation. If this isolation is compromised a small DC leakage current can flow from the DC input (truck's battery) to the AC output or the inverter's case.

Likelihood

Rare, but possible, especially if the inverter has been exposed to harsh conditions.

Why the Floating Neutral Doesn't Completely Protect You

A floating neutral inverter reduces the risk of electric shock compared to a grounded system in some scenarios, but it doesn't eliminate it entirely. It protects against a single ground fault causing immediate danger. However: Second Fault Scenario

If you were to touch the hot wire and there was a pre-existing ground fault (e.g., a damaged wire touching the chassis), you would complete a circuit and receive a potentially dangerous shock.

Capacitive Coupling/Leakage

As explained above, these mechanisms can provide a current path even with a floating neutral.

Steps to Investigate and Mitigate the Risk1. Thorough Visual Inspection

Check the inverter's case for any damage, cracks, or signs of overheating. Inspect the wiring connections for tightness and insulation damage. Ensure the inverter is clean and dry.2.

Leakage Current Testing (Important!)



Use a clamp meter designed to measure leakage current (AC mA range). Standard clamp meters are not sensitive enough. Clamp the meter around the AC output conductors (both hot and neutral) together. The meter should read close to 0 mA. A reading above 0.5 mA is a concern. Next, clamp the meter around the inverter's chassis ground wire (if it has one). Any significant reading here indicates current leakage to ground. Important Safety Note

Disconnect the inverter from the truck's battery before opening the inverter's case.3.

Insulation Resistance Test (Megger)

This test requires a megohmmeter (Megger), which applies a high DC voltage to measure insulation resistance. Test the resistance between the AC hot and neutral conductors and the inverter's case. A low resistance reading indicates insulation breakdown.

Important Safety Note

This test can damage electronic components if not performed correctly. Consult the inverter's manual and follow proper safety procedures.4.

Consider Bonding the Neutral (Cautiously)



Warning

This changes the behavior of the system and should only be done if you understand the implications.

Method

You could bond the neutral conductor of the inverter to the vehicle chassis.

Pros

Reduces phantom voltages and makes the system more predictable. Potentially reduces the capacitive coupling shock hazard (but not always).

Cons

Introduces the possibility of ground loops.

Considerations

If you bond the neutral, ensure the vehicle's electrical system is also properly grounded.5.

Professional Inspection

If you're uncomfortable performing the tests above or if you suspect a serious problem, have a qualified electrician inspect the inverter and the vehicle's electrical system.

Key Takeaways Floating neutral inverters have advantages, but they're not immune to shock hazards. Capacitive coupling and leakage current are common sources of minor shocks. Any perceptible shock warrants investigation and corrective action. Leakage current testing is crucial for identifying insulation problems. Consider bonding the neutral only if you fully understand the implications.* When in doubt, consult a qualified electrician.

Safety First! Electricity can be dangerous. Always take precautions when working with electrical equipment. If you're not comfortable with any of these procedures, seek professional help. Flag for review