Arcing vs. Melting Damage: How to Tell the Difference

Electrical fires leave a trail of evidence as they spread, and forensic fire experts read that trail as objectively as possible to determine the nature and origin of the blaze. The type of damage the fire caused to the electrical system can point to how it started. Arcing and melting damage are common in systems devastated by fire, but what are some differences between the two types of damage?

Underlying Cause

Arc damage occurs in an electrical system when electricity flows in an air gap between two ungrounded conductors of widely varying voltage. The short circuit that occurs can lead to an arc flash, or even an arc blast.

Meanwhile, melting damage usually occurs in systems with a high electrical current flow. Components and conductors can overheat from the electrical load and eventually begin to melt.

Visual Appearance

An arc flash is usually accompanied by a bright flash of light and a loud noise. It leaves a pattern of bead-like bits of scorched or melted metal in its wake, which forensic engineering services can analyze to trace the cause of the fire.

Melting damage is not as dramatic or immediately obvious. However, components that are encased in plastic or insulation are common targets for melting, and they may leave behind a sticky residue of melted plastic.

Telling the difference between Arcing and Melting is tricky, and requires an expert to evaluate the material.

How to Distinguish Arcing Damage

Arcing damage can be caused by loose connections, faulty wiring, damaged insulation, or exposure to moisture. Some physical signs of arcing damage on a copper wire are:

• Burn marks or scorch marks on the wire or the surrounding material, indicating where the arc has occurred.
• Charred or melted insulation on the wire, exposing the bare metal to the air and potential hazards.
• A pitted or eroded surface on the wire, where the metal has been vaporized by the arc and left behind small holes or craters.
• A curved or bent shape on the wire, where the arc has pushed the wire away from its original position and altered its alignment.
• A smell of ozone or burning plastic in the air, resulting from the high temperature and chemical reaction of the arc.

How to Distinguish Melting Damage

Melting damage can be caused by overloading, short circuits, power surges, or exposure to high temperatures. Some physical signs of melting damage on a copper wire are:

• A flattened or distorted shape on the wire, where the metal has lost its rigidity and flowed under pressure or gravity.
• A shiny or glossy surface on the wire, where the metal has melted and solidified, forming a smooth or irregular layer.
• A discolored or oxidized surface on the wire, where the metal has reacted with the air or other substances, changing its color or texture.
• A brittle or cracked surface on the wire, where the metal has become weak and fragile, breaking easily or splitting apart.
• A smell of burning metal or smoke in the air, resulting from the high temperature and combustion of the wire.

Potential Severity

Arc damage can be devastating to an electrical system if left unchecked. Those arc flashes and blasts can cause explosions and far-reaching fires in your facility.

Melting damage may be less dangerous to the entire system, but that doesn’t mean it carries no hazards at all. Melted wires and components can cause a failure in one or more parts of your electrical system. Once those components melt, there’s no way to fix them; you’ll have to replace them in full to boost your system’s overall safety.

If you notice arcing or melting damage around your electrical system, consider enlisting a forensic engineering expert to inspect the site. There are a few key differences between these types of electrical damage, but you should still mitigate both dangers to the best of your ability to maintain safety. Contact Dreiym Engineering to learn more about our forensic engineering consulting services.