Electrical switches, used to disconnect/ connect power, have a mechanism to handle flash over current via arcing contacts. Arcing during load break is a normal phenomenon. It is a result of interrupting an electrical signal with significant energy. When two conductive surfaces begin to separate, the electric flow wants to continue. It will continue through the air until separation is great enough to make the electrical arc lose its energy.
Manufacturers understand this and design systems to handle this phenomenon. They add an extra component, rated for the high heat which occurs during flashover.
Tungsten Arc Blades
Tungsten is a common material used as it handles the arcing heat well. It is imperative that this additional tungsten blade operates as intended.
Generally, this “arc blade” is the first part of the electrical connection to make contact during the closing of electrical disconnect switches, and the last part of the electrical connection to break contact during the opening.
Different voltage levels require different technologies, but the idea is generally the same: drag the electric arc between 2 conductors, increasing the distance between them and voltage will eventually lose the energy it needs to sustain itself.
Arc Blade System Inspection
It’s important these blade systems are inspected to make certain they are in working order. When an arc blade hangs up, the resulting mechanism may report the switch is open when in fact part of it still conducts electric power!
How often does this happen? Thankfully, not often. But as we all know in electrical safety, it only needs to happen once to kill a person.
There is NO substitute for a physical inspection, after the appropriate LOTO of the electrical & mechanical systems in use.
All the fancy advanced test apparatus which populates our industry these days are NOT a substitute for an experienced set of eyes to verify proper operation.
See the video for my case in point: this switch mechanism showed OPEN switch status, while the arc blade STILL was hung up and able to conduct 13,200 volts! Fortunately, this was discovered during a PM shutdown, was corrected and no one died.
Switch Mechanism With Arc Blade Hung Up.