The aging of connecting wires often does not "suddenly fail", but first emits some perceptible "distress signals". Based on multiple recent documents, common signals can be summarized into four categories: "look, touch, smell, and measure":

Look at the appearance

The insulation layer becomes darker, loses its luster, and develops yellow, gray, or charred patches or fine mesh-like cracks. Parts of it fall off, exposing copper/aluminum

. (Note: The original text appears to be an incomplete or ungrammatical Chinese sentence, hence the translation is also incomplete and ungrammatical. If the original text is intended to be a complete and grammatical sentence in Chinese, please provide the complete sentence for a more accurate translation.).

The plug, socket, and terminal block exhibit verdigris, white oxidized powder, or blackened traces

. (Note: The original text appears to be incomplete, so the translation is also incomplete. If the original text is complete, please provide it for a more accurate translation.).

The wire is stiff, produces a "crisp sound" when bent, or has wrinkles or cracks on its surface

. (Note: The original text appears to be an incomplete or accidental input, hence the translation is also incomplete and appears as a period.).

Touch the temperature/hand feel

Shortly after power-on, the cable becomes visibly hot (>50°C) when touched with the back of the hand (after power-off), or the connector is locally overheated

. (Note: The original text appears to be an incomplete or ungrammatical sentence, hence the translation is also incomplete and ungrammatical. If the original text is intended to be a complete sentence, please provide the complete text for a more accurate translation.).

When bending, if the wire feels hard and the insulation layer flakes or crumbles, it indicates that the material has become brittle

. (Note: The original text appears to be an incomplete or accidental input, hence the translation is also incomplete and insignificant.).

Smell the scent

During operation, a faint smell of burning, plastic, or pungent hydrogen chloride is often detected, which is mostly due to the overheating and decomposition of the insulation layer

. (Note: The original text appears to be an incomplete or ungrammatical sentence, hence the translation is also incomplete and ungrammatical. If the original text is intended to be a complete sentence, please provide the missing content for a more accurate translation.).

Measure performance (with the help of tools)

Insulation resistance meter: if the resistance is less than 0.1 MΩ in a damp 220 V circuit and less than 0.22 MΩ in a dry circuit, it is determined to be aged

. (Note: The original text appears to be incomplete or a typo, hence the translation is also incomplete and placeholder text is provided.).

Multimeter: If the DC resistance of a conductor is more than 1.5 times higher than the standard value of a new wire, it indicates oxidation or a reduced wire diameter

. (Note: The original text appears to be an incomplete or unintended input, hence the translation is also incomplete or placeholder text.).

Infrared temperature measurement: When fully loaded, the surface temperature rise exceeds 20°C or locally exceeds 70°C, indicating a risk of overheating

. (Note: The original text is an empty string, so there is no actual content to translate. If you have a specific text to translate, please provide it.).

Leakage protector: frequent tripping without new loads (leakage current > 30 mA), mostly caused by decreased insulation