Electrical safety

Electrical hazards

• Joule heating of human tissue
• Involuntary muscle contractions
• Ventricular Fibrillation

Resistance of Humans

• Ranges from 100\Omega to 1M\Omega
• Equivalent circuits for humans

Heart stoppage

Source: El-Sharkawi, Electric Energy

Step potentials

• Large currents flowing to ground can create hazardous voltage differences along the ground
• If the potential difference across a persons stride is high enough, a shock can occur

Step potentials

Source: El-Sharkawi, Electric Energy

Step potentials

Source: El-Sharkawi, Electric Energy

Step potentials

Source: El-Sharkawi, Electric Energy

Ground Fault Circuit Interruptor (GFCI)

• A ground fault circuit interruptor monitors the difference in current between the hot and neutral lines
• If the current is unequal, that means that another conductor is carrying current to ground, which is a hazardous situation.
• If Kirchoff’s current law is violated, something unsafe might be happening.

Ground Fault Circuit Interruptor (GFCI)

Ground Fault Circuit Interruptor (GFCI)

Fire Risk

• The earth is a ground in our grid, so trees can complete a circuit
• If a tree completes the circuit, current flows through the tree
• The electrical potential energy is converted to thermal energy
• Thermal energy can lead to temperatures high enough for ignition

Fire Ignition Diagram

Fire Circuit

Grid Upgrades

• Undergrounding lines costs between $2 million and $6 million per mile