For our purposes, one rule applies concerning safety around electrical apparatus:
If you have any doubt about whether or not something is safe, leave it alone. Let a professional electrician work on it.
Household voltage, normally about 117 V (but sometimes twice that for large appliances such as electric ranges and laundry machines), is more than sufficient to kill you if it appears across your chest cavity. Certain devices, such as automotive spark coils, can produce lethal currents even from the low voltage (12 to 14 V) in a car battery.
Consult the authority or your electrician concerning what kinds of circuits, procedures, and devices are safe and which aren’t.