What is Arc Resistant Switchgear? Working and Benefits

Arc resistant switchgear provides a safe way to protect workers and equipment from the dangers of an electrical arc. This type of switchgear uses an array of special features to prevent or reduce the effects of electrical arcing. To help you understand arc rated switchgear, we put together an overview of how it works, its features, and how it can protect workers and equipment.

What is Arc Flash?

Arc resistant switchgear is designed to help mitigate the harmful effects of an arc flash by helping to prevent, reduce, and channel it away from workers equipment. But what is arc flash and why is it so dangerous? Also, what causes it to occur?

An arc flash happens when current travels through ionized air. It’s usually an attempt by the current to move from one conductor to another. When this happens, an immense amount of energy is released.

The energy of an arc quickly converts into visible light and extreme heat. The heat makes the air to expand almost instantaneously. This is what causes the explosion. Situations that might trigger arcing include:

• A fault in an electrical system
• Damage to electrical equipment or insulation
• Poorly installed or maintained electrical equipment
• Human error, especially when workers are performing maintenance on live equipment

Switchgear Arc Flash

A switchgear arc flash is arcing that happens inside the switchgear assembly or enclosure. Arc flashes are common in circuit breakers when contacts separate, on high voltage switchgear isolators when they are opened, and in other devices.

A switchgear arc can also happen between adjacent components, especially when the insulation between them is worn or broken, or when a switchgear connection is loose, corroded, or damaged in other ways.

Arcing may also result from a tool connecting two conductors or an animal in the gear assembly. An operator may trigger arcing if they accidentally touch a live component. When switchgear arcing present a risk to workers, it becomes a top priority to invest in arc resistant equipment.

What is Arc Resistant Switchgear?

Arc resistant switchgear is simply switchgear that has been designed to protect operators from the dangers of arcing. It allows workers to safely maintain equipment without the risk of arc flash accidents and injuries. A switchgear arc flash can be dangerous in the following ways.

• First, the heat generated can be quite high, up to 35,000 degrees Fahrenheit. Such temperatures would quickly melt or vaporize some metals.
• Secondly, the pressure generated by an arc flash can result in dangerous explosions. Shock waves from a switchgear explosion caused by arcing have been known to cause panels to rupture and debris to come out flying.

In order to prevent a high voltage switchgear explosion and its associated risks, arc resistant equipment is used. This type of switchgear comes with special features to contain the arc as well as deflect it away from persons working on or near the switchgear.

Switchgear Arc Protection

Switchgear arc protection mainly involves the use of vents and duct system to carry away the super-hot gases and high pressures of an arc flash away from the switchgear enclosure and to a safe location. This can be in the area above the switchgear or outside the switchgear room.

Other arc flash protection methods employed by arc resistant switchgear include, but are not limited to, the following.

• Remote racking and switching of switchgear
• Using devices that reduce the time taken to clear an arc
• Using reinforced switchgear enclosures such as extra thick steel doors and additional hinges
• Including flame barriers in the enclosure assembly
• Using flaps that seal switchgear vents in the event of an arc fault

Workers who maintain and operate the switchgear must also wear the proper Personal Protective Equipment (PPE), which includes arc-rated clothing, gloves, face shields, and other gear. This is to offer an added degree of protection to prevent injuries.

Arc Resistant Switchgear Design

The construction of arc flash resistant switchgear varies depending on whether it’s meant to exhaust the energy of an arc flash within a building or outside. Generally, this type of switchgear will come with flaps that open under the intense pressure of arcing energy.

The flaps allow the heated gases of an arc flash and the pressure to safely vent out of the enclosure and away from the operator. When venting arc flash gases outside of the switchgear room is necessary, extra duct work is used.

Depending on the manufacturer guidelines, a specified height clearance from the floor to the room’s ceiling is required. Other features include those discussed earlier, such as reinforced switchgear design and using heavy duty steel.

Arc Flash Switchgear Rating

Arc resistant switchgear is defined as switchgear that is built to withstand the occurrence of internal arc flashes. These are defined by ANSI C37.20.7 standard, alongside the usual ANSI/IEEE and UL standards for electrical switchgear.

Unusually, the manufacturer will label the switchgear ratings for arc resistance and provide the operating conditions for which the tests are based upon. Arc flash gear ratings also result in several types of arc resistant equipment. These are discussed next.

Arc Resistant Switchgear Types

Arc resistant switchgear is designed with different arc mitigation capabilities as defined by the ANSI standard C37.20.7. Based on the standard, arc resistant switchgear types include type 1 and type 2. These offer varying accessibility features.

Arc Resistant Switchgear Type 1

Type 1 arc resistant switchgear is accessible in the front only. That means the operator is only safe when standing in front. This type of AR equipment is not widely used since it satisfies fewer arc resistant switchgear requirements.

Arc Resistant Switchgear Type 2

This type of arc switchgear provides arc flash resistance functionality all around its perimeter: front, back, and sides. Type 2 arc-rated switchgear is further classified as type 2B or 2C. The added suffix specifies the additional functionality. This is explained below.

Arc Resistant Switchgear Type 2B

The arc resistant switchgear type 2B is similar to type 2. However, it includes additional arc resistance functionality by being arc resistant when the low voltage compartment is opened. The added properties make it safer for operators to work with.

Arc Resistant Switchgear Type 2C

The 2C AR switchgear is the highest level of arc resistance. This includes features from both type 1 and type 2B, as well as an additional feature: being arc-resistant in the individual compartments. When it comes to arc resistant switchgear, type 2B is the most common and type 1 the least popular.

Conclusion

A switchgear arc can cause an explosion that can damage equipment, injure or kill workers, and start fires. This makes it a serious hazard in the switchgear room. To mitigate the risks associated with arc flash events, many electricians choose to install arc resistant switchgear. This type of switchgear is designed to contain and redirect the energy of an arc flash, protecting both people and equipment from its destructive force.