Low Voltage Distribution Board Safety

March, 2007

Published by Terry Chandler Director of Engineering, Power Quality Thailand LTD/Power Quality Inc., USA. Emails: terryc@powerquality.org, terryc@powerquality.co.th


Accidental Death is REAL!!

Electrical Shock Fatalities in the USA
  • Electric shocks are responsible for about 1,000 deaths in the United States each year, or about 1% of all accidental deaths.
  • Electric shocks cause death in 3-15% of cases. Many survivors require amputation or are disfigured by their burns.

Electrical Injuries
  • Electrical injuries can be caused by a wide range of voltages but the risk of injury is generally greater with higher voltages, and is dependent upon individual circumstances.
  • Electric shock
  • Electrical burns
  • Loss of muscle control
  • Thermal burns
Electrical Shock
  • A voltage as low as 50 volts applied between two parts of the human body causes a current to flow that can block the electrical signals between the brain and the muscles.
  • Stopping the heart beating properly
  • Preventing the person from breathing
  • Causing muscle spasms
Electrical Burns
  • If an electrical current passes through the human body it heats the tissue along the length of the current flow. This results in deep burns that  are permanently disabling.
  • Burns are more common with higher voltages but may occur from low voltage.
Loss of Muscle Control
  • An electric shock causes painful muscle spasms that can be strong enough to break bones or dislocate joints.
  • This  often means the person cannot ‘let go’ or escape the electric shock.
  • The person may fall if they are working at height or be thrown into nearby machinery.
Burn Injury Survival
Image: American Burn Association (1991-1993 Study), Published in 2006
The Hazards of Electricity – Do You Know What They Are? by D. K. Neitzel

Thermal Burns
  • Overloaded, faulty, incorrectly maintained, or short circuits  get very hot.
  • Even low voltage batteries (12V) can get hot and may explode if they are shorted out.
Arc Flash
Arc Flash has 3 issues
  • The arc temperature
  • The incident energy
  • The pressure developed by the expanding gas

The main concern is the arc temperature  and ignition of clothing.

Arc Flash Test

An arc flash test used a circuit adjusted to deliver 20,000 amperes at 480 V, 3 phase. The bright light is the arc.


Arc Flash Test 2

As the arc develops (second from top), it melts and vaporizes the metal of the electrodes and the box.


Arc Flash Test 3

This vaporizing metal  expands outward with the pressure wave, and the test stand is enveloped in the arc flash explosion.


Arc Flash Test 4

The duration of the arc was about 0.045 sec. The test was set up at the Square D High Power Lab in Cedar Rapids, IA.


Arc Flash Result
Outdoor gear following arc flash

Approach to Energized Part
Image: Illustration of Boundaries , Published in 2006
The Hazards of Electricity – Do You Know What They Are? by D. K. Neitzel
Image by Creative Safety Supply: https://www.creativesafetysupply.com/qa/arc-flash/how-to-determine-ac-flash-boundaries

Safety Requirements by Category 0 to 4

Arc Flash Protection

Dressed for Safety
Photo: Salisbury by Honeywell

Arc Flash labeling in USA

Safety Review
  • Shock hazard
  • Burn hazard from electrical current
  • Burn from thermal (hot wires)
  • Explosions due to Arc Fault

Some Safety Tips
  • Never work alone on electrical circuits.
  • Use lock outs to prevent accidental circuit activation.
  • Wear protective gloves, eye and face protection and clothing.
  • Double check the expected voltage before work.
  • Always deenergize circuits if at all possible.
  • DO NOT ASS-U-ME the circuit is off.
  • Always make sure the area around your feet is clear.
  • If a ladder is necessary it should be fiberglass.

BE SAFE!!!

Image by Energy Management Corporation: How to Assess Your Equipment for Arc Flash Hazards

Published by PQTBlog

Electrical Engineer

One thought on “Low Voltage Distribution Board Safety

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s