Hot Spot
A point in the circuit producing excess heat locally because of a high-resistance connection or a narrowed cross-section. The power produced is the square of the current times the resistance; so even if the resistance looks small, the heat rises quickly as the current grows. It can usually be noticed before a fault occurs.
In a healthy circuit the heat is spread evenly along the cable. If one point is noticeably hotter than its surroundings, there is extra resistance there. The source can be a loose terminal block, an oxidised contact, an insufficiently crimped lug, cut strands or a joint with an undersized cross-section.
- Detection: scanning with a thermal camera or non-contact thermometer while the load is running; if no instrument is available, cut the power, confirm that no voltage remains at the terminals and then make a comparative check. A hot spot may have reached a temperature that causes burns; do not touch it directly with a bare hand.
- Verification: measure the voltage under load between the two sides of the suspect point. A value above 0.5 V counts as a fault.
- Risky locations: fuse holders, battery terminals, the main chassis bolt, connector pins, terminal blocks that have not been serviced for a long time.
In DC motor and driver installations drawing high current, hot-spot scanning is one of the few faults that can be caught before it turns into a fire. Do not leave the point you find merely retightened; clean the surface and renew the terminal.
Context in which this term is used: Installation, redundancy and field continuity