What is the reason why the electrical shell does not leak electricity, but the test pen can light up?
The main reason is that there will be induced electricity in the metal casing. This induced electric current is very small and can be ignored in normal times. However, when the fingers and shoes are relatively wet (for example, just after taking a shower), they will feel numb. Main reasons: There is a problem with the ground wire (virtual connection or has been disconnected), the metal casing is not well grounded, and the neutral wire and live wire are reversed (most electrical appliances can work normally when they are connected to zero fire, but some very strange things will happen)
