Defected connections make up the majority of electrical related issues identified with thermography.
In a distribution panel each connection and fuse has a very small resistance. When current passes through a circuit it’s components heat up. As a connection deteriorates the resistance increases with a corresponding increase in temperature. When the temperature rises above a pre-determined value, the component is deemed as defective.
It is important to recognize the thermal gradients associated with defected connections on electrical components.
An increase in electrical resistance on a connection will cause localized heating. Heat is conducted away from the local resistance, thus creating a thermal gradient.
Example below – A contactor and overload relay unit. Defected connections identified on contactor on phase2 & 3. Excessive overheating is identified between the contactor and the overload relay unit. This indicates that the contacts at this point are defected. In this arrangement the links are part of the overload assembly. If damaged the overload unit should be replaced.
When a connection is identified as defected it does not always mean that it is loose.
It can be oxidized, corroded, or have dirty contact surfaces. There may be a problem with the cross threading or the wrong bolt or screw could be in place. The connection can be wrongly sized or the conductor strands could be broken away from the fitting.
Often, applying a specific torque (or re-tightening) will not solve the problem.
Where defected connections are identified they should be dismantled and investigated. Contact surfaces should be cleaned and remade, applying the correct pressure to restore full electrical contact.
Excessive overheating (as in our example) at either terminal connection or contacts causes cable insulation damage and pitting of the contacts, therefore accelerating their temperature rise. Wires and components should be replaced if subjected to excessive overheating (as in the example image above).
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