## 6 Discussion
### Mechanism behind Glowing Connections and Arc Faults  
From the results of our experiments, we were able to deduce the mechanism behind series arc faults for copper-based contacts. The flow chart for the mechanism is shown in Figure 15.  
A fire hazard from a glowing connection can be accelerated by an arc fault, as is explained in the steps below.  
1. An initial electrical discharge produces small patches of insulating oxides.
2. A repeated discharge in the same location, such as what is caused when a plug is repeatedly removed from and reinserted into a socket during normal use, increases the area of the oxide patches.
3. Once the insulating patches, or the bulge, on the surface have increased to the point where the contact area is exhibiting overcurrent, the process will begin to produce heat through the Joule heating effect. At this stage, the process can be classified based on two main hazards. The first hazard occurs when there is no movement (insertion and reinsertion) of the plug. In this case, residual heat accumulates to the point where oxides can be created from the dissipation heat alone. The second hazard occurs when the contact surface moves so that it is no longer firmly connected, resulting in a vibration being created from the poor contact surface. This can induce a continuous electrical discharge that then greatly increases the temperature of the affected area, to the point where copper is able to oxidize with the atmosphere. Even if the contact area has already formed an oxide bridge, current can still pass through normally. This current flow, however, is not efficient. A small perturbation near the contact point by the operator or the environment can create a small initial spark that could then increase the temperature of the oxide patch near the affected area. If the spark is energetic enough, it can increase the temperature of the patch to the point where the oxide behaves as a semiconductor. A glowing connection or arc fault may then be initiated.
4. In a lower-current setting, a glowing connection can continue so long as there is current being provided and the resistance from the oxide bridge is not high enough  
Figure 15: The process that leads to electrical fires from accumulated heat and arc-fault states.  
to block the current flow. In a high-current setting, a glowing connection can be extremely energetic, so much so that it could melt off part of the oxide bridge. This could potentially split the bridge into two parts. In this case, the current flow stops. On the other hand, in the case where the oxide bridge grows to such a size where it cannot easily melt and break the contact, it will continuously leech copper from both contact surfaces and grow further still. Eventually, a certain size is reached such that the arc fault stops completely, and the glowing connection takes full effect.
5. Once the glowing contact area has been de-energized, the oxide bridge cools down to the point where the copper oxide behaves as an insulator. In this case, the contact surface does not pass any current. If the contact area has a small oxide bridge or a patch of conducting surface, then the contact area with the oxide bridge is able to pass current. The temperature of the small patch of conductive surface may increase due to overcurrent. If the temperature rises to the point where the majority of the oxide bridge changes its state back into a semiconducting phase, then the glowing connection will revert back to the state in step 3. The cycle will continue until the oxide bridge is broken or it is too large to pass current when the circuit is de-energized.