What Causes An Arc Flash?

What Causes An Arc Flash?

Slipped tools or hands
Falling parts
Dust, water, corrosion, oil
Animals
Sometimes there is no known cause
When arc flashes occur by accident, they can sometimes be caused much like the way they are
made on purpose.
An accidental slip of a tool, a loose part, or even your hand touching live parts can provide the
start the current needs to jump from one cable to the next.
Loose connections in the electrical equipment, improper installation, and parts that break and
fall are other possible triggers.
Dust, water, impurities, contamination, corrosion, oil, and grease can also provide a starting
route for the short circuit.
Even animals or bugs can get into electrical devices and start an arc flash.
Typically there is a reason for arc flash accidents, although we may not always know what it
was.

High Voltage Short Circuit

A short circuit, as shown in this next video, does not have a load providing resistance. The arc
that forms goes right through the air with little‐to‐no resistance.
The same thing happens in an arc flash. The circuit is completed straight through the air.

Select whether the following refer to a safely completed circuit or a short circuit that could lead
to an arc flash

safely completed circuit
Turning on a light in an office
Starting a motor control device
short circuit that could lead to an arc flash
Accidentally touching the wires in a panel box with a screwdriver
Splashing water on energized high voltage electrical equipment

What Is An Arc Flash?

What Is An Arc Flash?

Now that we have a good idea about electricity and shock, we can finally get into what an arc

flash is and just how dangerous it can be.

An arc flash is a short circuit through the air in an electrical panel box or any other piece of

energized electrical equipment. Air, as you have already learned, is normally an insulator, but

with a high enough voltage, a slipped tool, or a panel box that is dirty, the circuit can be

completed, causing a short.

When the short happens and the circuit is completed through the air, the air breaks down to

where it offers little‐to‐no resistance to the flow of electricity.

Remember, this is what a short circuit is. A short circuit will have almost zero resistance and will

have very high levels of current. The high current is what is responsible for the arc flash.

The tremendous amounts of energy released in an arc flash make for a very bright, very hot, and

very loud explosion.

Arc Flash vs. Safely Completed Circuits

Higher than normal currents

Now in a safely completed circuit, such as when a motor turns on a manufacturing line, the

circuit is complete, just like in an arc flash, but a safely completed circuit has a load on the

circuit offering resistance.

So in a safely completed circuit, the resistance affects the current in the circuit, keeping the

current under dangerously high levels.

Think of a lamp plugged into the outlet of your house. When you turn it on, the circuit is

completed, but the light bulb has resistance, so the current stays within safe limits.

If you were to stick a paper clip in an outlet, the circuit will also be completed, but this time it

will be a short circuit because the metal paper clip offers very little resistance to the flow of

electricity.

By the way, NEVER stick a paper clip into an electrical outlet. It is dangerous, and if you do it you

will receive an electric shock or worse

How Shock Is Measured

How Shock Is Measured:

I = V / R

To understand how electric shock can hurt you, let’s go back to the equation from Ohm’s Law

that had current on the left side, I equals V divided by R, or current equals voltage divided by

resistance.

Remember that voltage will often stay the same, so the current will depend on how much

resistance there is in the circuit.

If resistance is high, the shock will not be as bad as if the resistance is low. Higher resistance,

then, is better.

Resistance is reduced if you are wet or sweaty, or are not wearing the proper gloves or shoes,

making current (the part that kills you) much greater.

True of false?

When trying to stay safe around electrical hazards, keeping work areas dry and wearing proper

clothing can help keep your body’s resistance high and help keep you from getting shocked. ‐

true

Causes of Electric Shock

Causes of Electric Shock:

There are many ways that a person’s body can become part of an electrical circuit and get

shocked.

You will get an electric shock if you touch a live wire and an electrical ground or if you touch a

live wire and another wire of a different potential.

So, if you touch any live wire and then touch either a different live wire or a ground wire, you

can get shocked.

Electrical Devices

Electrical Devices -1

Fuse
Ground
Fault/ground fault
Receptacle
Plug
A fuse is a protective device that can open a circuit if there is too much current flowing through
it. Since a fuse melts when there is too much current, it protects the rest of the circuit from being
damaged.
Ideally, the fuse will be the weakest point in the circuit and will be the only place that a circuit
will melt.
If a circuit is grounded, it means that the circuit is physically connected to earth ground by a
conductor. This connection to the actual ground, or dirt outside, allows unwanted electricity to
flow to the earth.
Being grounded can prevent the buildup of static electricity and can help prevent electric shock
from faults.
A fault is temporary, unexpected current in a conductor. A short circuit is a type of fault that
allows damaging amounts of current to flow through a circuit.
An arc flash is a type of short circuit.
A receptacle is an outlet for electricity. You have these all over your house and plug items such
as irons and vacuum cleaners into them.
A plug, then, is what gets plugged into a receptacle, allowing an electrical device to get
electricity.


Load
Personal protective equipment (PPE)
Panel board
Transformer
A load is any device that converts electrical energy into light, sound, motion, or heat. One
example would be a light bulb.
A load gives resistance to the current in a circuit.
A light bulb is a load in a circuit that converts electricity into light.
Personal Protective Equipment, or PPE, is clothing and other items that are worn to help keep
you safe when working near arc flash hazards. PPE protects you from the intense light, heat,
sound, and explosion of an arc flash.
The type of PPE required is determined by the amount of voltage and current available. We will
cover determining what type of PPE is needed later in the training.
A panel board is a cabinet containing a group of circuit breakers, fuses, and short circuit
protection devices for lighting, appliances, or other circuits; it is usually placed in or on a wall
with access to the front through a panel door.
You have an electrical panel in your house where the circuit breakers are located.
Transformers help electricity travel over long distances without losing much energy.
Transformers are the only way to get electricity cheaply to your house.
Transformers allow electricity to get to your house by taking the high‐voltage, low‐current
electricity from the power lines and turning the electricity into 120 volt, higher current
electricity.

Transformers are important when learning about arc flash because one of the key components
of how bad an arc flash will be is how much current is available from the transformer supplying
the electricity.

Changes in Voltage, Current, and Resistance:

Changes in Voltage, Current, and Resistance:

If resistance stays the same, then voltage determines current
If voltage stays the same, then resistance determines current
Current is dependent on the voltage and the resistance
Staying with the similarities between electricity and water, let’s see what happens when voltage
and resistance change.
When voltage in a circuit changes, with resistance staying the same, current changes.
If you hook up a light bulb to a 1.5 volt battery, and then change the battery out for a 9 volt
battery, the light will shine brighter due to more current flowing through the circuit because of
the higher voltage.
The resistance comes from the light and does not change.
Similarly, if you increase water pressure in a pipe, more water will flow through it.

When resistance in a circuit changes, with voltage staying the same, current changes. In an arc
flash, resistance drops close to zero on a high voltage circuit, leading to current drastically
increasing, and creating an explosion.
Similarly, if you accidentally cut into a high volume, high pressure water pipe, the sudden
explosion of water could harm you.
Current is difficult to control in a circuit. That is why it is so important to be aware of arc flash
hazards. The rapidly increasing current in an arc flash can cause life altering injuries and even
death.