Why is 480V so dangerous?

electrical technician inspecting equipment

We hear it all the time:

“Can 480V produce large arc flashes?”

The short answer? Yes. 480V is prone to large arc flash incidents due to its voltage level and typical fault currents.

Voltage alone doesn’t tell the whole story. In fact, not only is 480V a dangerous shock hazard, but it is one of the most common and dangerous voltages for arc flash.

Let’s break that down and explain how current and clearing time are even more important.

Arc Flash Is About Current and Time—Not Just Voltage

When it comes to arc flash, two factors really affect arc flash size:

1. Available fault current

2. Clearing time (how quickly a breaker or fuse isolates the fault)

If a fault occurs, say, a tool bridges two conductors, in a small fraction of a second, an arc flash will occur. The arc flash continues until the upstream protective device opens the circuit and clears the fault. This can happen fast, but in electrical terms, even a quarter or half-second is a long time. The longer it takes for the fault to clear, the larger and more dangerous the arc flash becomes.

So yes, voltage plays a role, but the real danger lies in the amount of current that can flow during the fault and how long the fault lasts.

Why 480 Volts Is the “Sweet Spot” for Arc Flash

From an arc flash perspective, 480 volts is frequently the worst-case scenario. It’s high enough voltage to allow arcs to form and sustain themselves, and it is usually accompanied by a tremendous amount of available fault current.

Here’s why:

• High available fault current. Higher voltages require less current, and lower voltages require more current to deliver the same amount of power (this is why power is transferred over long distances at high voltage). A 12,470V system might only have 3000A of available fault current; alternatively, a 480V system with the same power requirements might have 70,000A of available fault current.

  
  

• 480V faults are particularly good at sustaining arcs because:

  
  

  • 480V is a three-phase system, and at least one phase is always delivering power to feed an arc (in contrast, single-phase voltage crosses zero 60 times a second and self-extinguishes)

    
    

  • 480V is more than enough potential to maintain an arc between conductors once initiated. In other words, 480V hits the “sweet spot” with both voltage and current.

It’s Not Just About Voltage. It’s Also About How Long the System Allows the Fault to Exist

Think of it this way:

An arc flash is like a burst pipe.

• Voltage is the water pressure.

• Current is the rate of flow of the water (think gallons per second).

• Clearing time is how long it takes to shut off the valve.

It’s not just the pressure (voltage) that causes damage; it’s how much water (current) comes through and how long it spills (clearing time).

The Bottom Line

If you’ve ever thought, “480 volts can’t be that dangerous,” think again.

480V systems are among the most common culprits for serious arc flash incidents.

Voltage alone doesn’t determine risk; current and clearing time also play major roles.

Three-phase systems (like nearly all industrial setups) are especially hazardous as they can sustain an arc.

Still have questions about your system’s arc flash potential? Don’t guess. Contact the experts at Guidant Power. We’ll help you understand the actual risk and ensure your team stays safe.