You've raised a critical and complex issue about the effectiveness of GFCI protection in the presence of non-sinusoidal leakage currents. Here's a breakdown of the situation and considerations

Key Points & Concerns:
UL 943 & Sinusoidal Faults

The UL 943 standard, and similar standards in other regions, is primarily designed and tested based on sinusoidal leakage currents. The 6mA trip threshold within 1 second is specifically defined for this type of current.

Non-Sinusoidal Currents & GFCI Behavior

Non-sinusoidal currents, particularly those with high crest factors (as you've observed with your Apple charger), can significantly affect how a GFCI responds. Here's why:

RMS vs. Peak

GFCI's, in their basic design, often rely on detecting the average difference in current between the hot (line) and neutral conductors. RMS (Root Mean Square) provides a useful measure of power delivered. However, the GFCI needs to respond quickly before that average becomes dangerous. The peak current is what causes the immediate danger to a person. A high crest factor means the peak current is significantly higher than the RMS current.

Harmonic Content

Non-sinusoidal currents are composed of multiple harmonic frequencies. GFCI circuitry may not respond equally well to all frequencies. The GFCI's detection circuit might attenuate certain harmonics, effectively reducing the perceived fault current.

Capacitive Coupling

Switch-mode power supplies (like those in phone chargers) often have significant capacitive coupling between the primary and secondary sides. This coupling can create leakage currents that are rich in harmonics and can have high-frequency components that some GFCI designs struggle to detect reliably.

GFCI Design Variations

Different GFCI manufacturers (and even different models from the same manufacturer) may employ different detection methods and filtering techniques. This can lead to variations in their sensitivity to non-sinusoidal currents. Some are designed to be more tolerant of nuisance tripping, which may inadvertently reduce their sensitivity to legitimate faults in the presence of harmonic distortion.

Your Experiment & Implications

Your experiment highlights a potentially serious vulnerability. The fact that you can sustain nearly 100mA RMS leakage current with a high crest factor, even with a load on the 5V side, suggests the GFCI isn't providing adequate protection under these conditions.

Safety Concerns

This is a critical issue because:

Electric Shock

A leakage current of 100mA RMS, even with a high crest factor, is more than enough to cause a serious, potentially fatal, electric shock if a person comes into contact with the energized surface.

Lifted Neutral

Your scenario about a lifted neutral on a switch-mode power supply is very relevant. If the neutral is lifted, the return current may find an alternate path to ground, potentially through a person who touches the equipment. The GFCI might not trip under these circumstances due to the harmonic content of the leakage current.

What should be done?1. Test Multiple GFCI Brands/Models

Repeat your experiment with GFCI outlets from different manufacturers (e.g., Eaton, Siemens, GE, Square D) to see if the results are consistent. Document everything thoroughly.2.

Sophisticated Measurement Equipment

Use an oscilloscope with a current probe to precisely measure the leakage current waveform (including peak values, harmonic content, and frequency spectrum) when the GFCI is not tripping. This data is crucial for understanding the behavior of the GFCI.3.

Consult with an Electrical Engineer

Present your findings to a qualified electrical engineer with experience in power systems and GFCI protection. They can help you analyze the data, determine the underlying causes of the behavior, and recommend solutions.4.

Contact GFCI Manufacturers

Share your findings with Leviton (and other manufacturers if you find similar behavior). Give them the details of your experiment and ask for their feedback. It's possible they are aware of this issue and are working on solutions, or they may want to investigate further.5.

Report to Regulatory Agencies

If you believe the GFCI is not providing adequate protection under normal operating conditions, consider reporting your findings to relevant regulatory agencies (e.g., UL, CSA, or your local electrical safety authority).6.

Modify Wiring

As a temporary modification, consider wiring the outlet without the GFCI. Then consider adding some sort of isolation transformer between the outlet and the equipment. Be sure to follow the electrical code, and consult with a licensed electrician.

Important Considerations



GFCI's are not a substitute for proper grounding. GFCI's protect against line-to-ground faults, but they don't prevent shocks from line-to-neutral faults. Testing

GFCI's should be tested regularly (monthly) using the test button to ensure they are functioning correctly.

Arc-Fault Circuit Interrupters (AFCIs)

While not a direct solution to your specific problem, AFCIs are designed to detect arcing faults (which can be caused by loose connections or damaged wiring). AFCIs and GFCIs provide complementary protection and are often required in combination in modern electrical installations.

Double-Insulated Equipment

Using double-insulated (Class II) equipment can reduce the risk of leakage currents because there is no exposed conductive part that can become energized.

In summary, your findings raise valid concerns about the effectiveness of GFCI protection in the presence of non-sinusoidal leakage currents. It's crucial to investigate this further and take appropriate steps to ensure electrical safety. Flag for review