The severity of electric shock depends on three components: the source voltage, the amount of current flowing through your body and your body’s natural electrical resistance.
Voltage is what most people focus on when discussing electric hazards. So what constitutes a hazardous voltage?
The Health and Safety Executive puts the minimum hazardous voltage at 50V AC and 120V DC.
Other agencies and organisations around the world recommend a minimum hazardous voltage of 30V AC.
But voltage is only one component of an electric shock. The seriousness of it also depends greatly on current and your body’s resistance.
Let’s discuss each individually.
You may have heard the phrase, ‘it’s not the voltage but the current that kills’. In a way this is true since current is what actually flows through your body and affects your muscle and nerve function.
But current on its own is not enough to deliver a serious shock. It needs a strong enough voltage and enough contact time for current to flow.
With sufficient voltage, current above 10 mA can cause an electric shock. Current over 100 mA (0.1A) can easily be fatal.
Your body is naturally resistant to current flow. If your skin is dry, resistance can be as high as 100,000 ohms. Wet skin drops that to as low as 1,000 ohms, which allows much higher current to flow through.
That’s why touching an exposed live wire or terminal with wet hands greatly increases the risk of electric shock.
High voltages can also reduce your skin’s insulation capability, what’s known as dielectric breakdown. This causes a drop in resistance and an increase in current flow.
To be safe, assume any power source is hazardous and treat it with care. If you are working on a socket, switch or live wires, use a voltage tester to check if there is live voltage.
You can also use a multimeter to check exactly how much voltage is flowing through the circuit.