Discharging Capacitors

Capacitors are widely used in Electrical and Electronic applications.  They are used in filter circuits, for power factor correction, for starting motors and for a host of other applications.  Capacitors store electric charge and can retain it for long periods, even days and weeks.  Hence, they can cause a severe electric shock or burns when someone accidentally makes contact with them even when the equipment has been switched off.

Thus, when an equipment is being repaired, it is essential to ensure that the capacitors inside are safely discharged. 

There are three common ways of discharging capacitors.  The first is by shorting the leads with a metallic object such as a screw driver or a wire.  This method causes a rapid discharge of the capacitor as the leads are shorted.  This results in excessive current which can melt the leads of the capacitor.  The molten metal can be thrown around the equipment damaging components and even causing damage to people nearby (in the eyes and skin).  Hence, this method should not be used.

The second method is to discharge the capacitors with filament lamps.  By connecting a filament lamp of the appropriate voltage lamps, the capacitor can be discharged.  The lamps glow initially due to the presence of the charge.  The light, then slowly diminishes indicating the discharge of the potential.  If the voltage is higher than the voltage rating of the lamp, two or more lamps can be connected in series. 

The third method of discharging capacitors is by the use of resistors.  A resistor with a suitable wattage rating can gradually discharge the capacitor.  This is the most ideal method of discharging capacitors.   (See also article on Bleeder Resistors)