Leakage Current and Capacitance

Discussion in 'General Electronics Chat' started by Management, Apr 8, 2010.

  1. Management

    Thread Starter Active Member

    Sep 18, 2007
    Can someone explain to me the relationship between leakage current and capacitance?

    Next can you tie that in with how the capacitive component of leakage current can cause nuisance trips to occur in a GFCI/GFI?

    I probably didn't ask the questions properly so if confused I can try to explain.

  2. SgtWookie


    Jul 17, 2007
    All capacitors have SOME leakage, even if it's hardly measurable. It's not a perfect world.

    Aluminum electrolytic capacitors typically have higher leakage than other types. Very basically, the higher the capacitance rating, the greater the plate area, and the greater the leakage rate. Current leakage is one cause of power dissipation in the capacitor.

    If the capacitor's power dissipation becomes high enough, the electrolyte solution in the capacitor will boil, causing catastrophic failure of the package. Aluminum confetti will be everywhere.

    Polarized electrolytic capacitors can frequently be re-formed. I've attached a very old document (ReformerNo1.pdf) from WWII days that contains tables of cap values vs voltage rating vs acceptable leakage rates, and details how to use an ancient capacitor dielectric re-former. It's about 4mb in size, and interesting from both a practical and historical aspect.

    I've also attached a more modern cap re-former "how-to" guide.

    GFCI breakers sense the difference in current flow between neutral and hot, and also sense current in the ground path. Actual current limits may vary a bit between manufacturers, but if the difference or ground current is more than a few mA's, the circuit will be interrupted.