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Aircraft Maintenance TroubleShoot > Alcor EGT and CHT Troubleshoot

What do the different Alcor EGT probe lead colors represent?

Red and yellow wires are type K. Type K is composed of chromel and alumel wire. Red is negative. Type K is the most common. Red and brown/tan wires are type E. Type E is composed of chromel and constantan. Red is negative. Alcor's CHT system has type J wires. Type J is composed of iron and constantan wire. The wires are black and yellow, with yellow being negative.

Most aviation EGT and CHT Systems are based around three types or thermocouples. The most common, type K, has red (-) and yellow (+) wires and is used on most EGT systems. It uses chromel and alumel wires in the element and lead.

Type E thermocouples were used on the earlier EGT Systems. They have red (-) and brown or tan (+) color codes and are composed of chromel and constantan wires and elements and produce twice the voltage of K type. Many CHT Systems use a type J system or iron and constantan metals. They have either black (+) and yellow (-), or red (-) and white (+) color codes.

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