What Causes Electrical Arcing?

Most everyone in the world has seen an electrical arc. Lightning, certain short circuits, and other times when there is literally electricity moving through the air are all Arc Flashes. We’re going to look into the fundamental causes of electrical arcing.

 

Moving Power

Electricity is essentially a charge being conducted through a wire. All electrical charges want to disperse as quickly as possible. They’re like water behind a dam: it always wants to get out. In the case of electricity, the charge wants to disperse, positive to negative. It always wants to get to ground.

The problem with this is that we want to actually use the electrical charge, so it can’t go straight to ground. We use insulators to keep the electricity essentially safely inside the wire. Without the insulator, the charge would get out and work it’s way to ground like water out of a burst pipe following gravity. Insulators can be a wide range of things. The rubber casing around wire is it’s insulator. The gigantic, ceramic cones on utility poles are insulators that prevent the charge from trying to discharge into the wooden pole.

The air itself is also an insulator. Electricity generally does not want to move through the air. This is why we can have electrical sockets exposed to the open air, but not to water. The air won’t easily conduct an electrical charge but the water will. Water isn’t a great conductor, but it’ll ruin your day.

 

Conducting in the Air

The air is only mostly an insulator. When there is enough power concentrated in a conductor, the air becomes another viable path to ground. This force to move is Voltage, essentially the electrical equivalent of Pressure. When there’s enough pressure, the charge is squeezed out into the air. You can think of this as being the same as blasting water uphill: water at rest won’t go uphill, but pressurized water will.

When the charge gets out into the air, changes start to happen. The charge massively heats the air, creating plasma. Neon lights contain gasses we heat into plasmas to make them glow. In this case, we’ve turned the air into a gigantic, neon sign. Plasmas have basically no resistance and extremely high current carrying capacities. Every amp (every ‘gallon’ if we’re sticking to water analogies), is going to blast through that arc of plasma.

This has some immediate hazards to it. Immediately, there is the absurd voltage and amperage in the air. 120 volts feels like a scary tingle, it’s numbness on over drive, fuzz in your body. Arcing voltages and amperage will fry your body like a cockroach under a rocket launch.

Secondarily, your body, the air, and the conductors have lots of resistance with this much power in play. Resistance is essentially friction from molecules and charges moving. It’s the change of electrical current to thermal energy. What happens when you heat up metal? It melts. What if you heat it really fast? It skips being a liquid and becomes a gas, it sublimates. Generally sublimating things will explode. The pressures involved in the change of volume force the gas to expand, blowing apart anything that hasn’t yet become a gas.

You are already a liquid, so your body won’t sublimate with an extreme electrical charge. Instead, if the energy does anything more than burn, if it heats you up, it’ll cause the water in your body to flash into steam and… you’ll essentially explode. That is of course, a worst case scenario. In lesser cases, the bigger problem is third degree burns, nerve damage, your organs being cooked on the inside, and your heart stopping.

The conditions that create arcs will cause bodily harm, start fires, and destroy equipment.

 

Causes of Conduction

As scary as it is, this sort of electrical arcing is common. In some applications, it’s expected and designed for. In others, it’s not expected, not planned, and incredibly terrifying.

  • Electrical Contacts
    A key component of electrical arcing is proximity to a conductive surface. When electrical contacts are closed, power flows from one to the other smoothly. When the contacts are separated, there is a brief period in which the voltage will arc between the contacts. The resistance of the small amount of air between the contacts isn’t enough to prevent the arc. Special designs, inert gasses, and even insulating oils are used to prevent or mitigate this arc’ing and the damage it causes.
  • Static Charges
    The static charge you experience from walking on a fuzzy surface and then touching a doorknob or other metal object is another type of electrical arc. This is a tiny, harmless event. You carry the charge, but while you’re isolated from ground, it’s harmless. Once you’re grounded, the charge leaves you with a little sting as it arcs to the conductive surface on the way to ground.
  • Circuit Boards
    Well designed electronics contain designs to handle extreme electrical charges. This includes a Spark Gap. These are pointed features in a circuit that direct a spark across contacts safely. Some designs even use Gas Discharge Tubes, essentially little neon-light-like tubes that disperse excess charges.

The less planned for arc cause is hardware failure. There are numerous ways for hardware to fail. It could be dropping a screw driver on high voltage contacts. It could be touching something you really shouldn’t. It could be a piece of heavy equipment melting and blasting a charge out of safely contained, insulated conductors.

 

 

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