Basic Electrical Safety

Safe Voltage Levels

The fundamental approach to protect against electric shock is to prevent contact with voltages that can cause a hazardous current through the body.  Voltages above 30 Vrms or 42.2 volts peak or 60VDC are considered great enough to potentially cause a lethal electric shock to humans.  Much of electric safety is concerned with avoiding human contact with voltages of this level under both normal operating and fault conditions.

Electric Shock and Wet Locations

The discussion so far has been about dry locations, but what if conductive fluids are involved in the contact surface that delivers the current to the human body?  Conductive fluids will greatly increase the amount of current through the human body that will be produced by a given voltage. In these situations the focus is not on limiting current but with limiting the amount of current that can be supplied by a circuit under fault conditions.  Normally this is done with a Ground Fault Circuit Interruption (GFCI) device – also known as a Earth Leakage Circuit Breaker (ELCB).  The problem here is that there is disagreement among international standards on the issue of how much current must pass through the body for it to be an electric shock concern. However, within the semiconductor industry 5mA has been accepted as a maximum limit. This is consistent with the number given in the US National Electric Code.  This means that if electric shock is a concern in a wet location, the current available to a ground fault should be limited to 5mA.