Electrocution instantly causes the muscles in a person's body to tense up. This is dangerous because it means a person holding a live wire can't let go. 

Ideally, you'll be able to turn off the source of the electricity in this kind of situation, Alex Elderfield explains. But if that's not possible, you can help the person (without getting electrocuted yourself) by breaking the circuit. The simplest way to do that is to find a long hard object, like a stick, and give the person a firm whack.