junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
Not being a code expert, could not find any direct code reference (if any) to adding an inductor to the grounding conductor.
Added in user equipment.. Had a lab technician add a GFCI protected extension cord with a fairly elaborate GFCI circuit to a test setup, and complained about the GFCI always tripping when turning on the test.
Measured trip on cord GFCI at 4.1 mA 60 Hz but in operation measured less than 100 uA 60 Hz leakage after installing a 5 mH inductor in green wire inside power supply..
The GFCI extension cord with integral GFCI is used to supply a 3000 V isolated switch mode power supply switching at 140 kHz, NO grounded EMI filter capacitors. The 140 kHz common mode leakage current was tripping the GFCI. The FETs in the SMPS have about 40 pF capacitance to ground.
I know this is not NEC covered since the inductor was installed inside plug in equipment; however,
if I had chosen to add the inductor on the green wire to a GFCI outlet in a plastic box, would that be any type of code violation? The inductor not much more that a multiturn ferrite bead.
Added in user equipment.. Had a lab technician add a GFCI protected extension cord with a fairly elaborate GFCI circuit to a test setup, and complained about the GFCI always tripping when turning on the test.
Measured trip on cord GFCI at 4.1 mA 60 Hz but in operation measured less than 100 uA 60 Hz leakage after installing a 5 mH inductor in green wire inside power supply..
The GFCI extension cord with integral GFCI is used to supply a 3000 V isolated switch mode power supply switching at 140 kHz, NO grounded EMI filter capacitors. The 140 kHz common mode leakage current was tripping the GFCI. The FETs in the SMPS have about 40 pF capacitance to ground.
I know this is not NEC covered since the inductor was installed inside plug in equipment; however,
if I had chosen to add the inductor on the green wire to a GFCI outlet in a plastic box, would that be any type of code violation? The inductor not much more that a multiturn ferrite bead.