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What derating factors are applied to contactors at altitude?

For the most common Tesys D range of contactors:
No derating bellow 3000m altitude for voltage and current in the power poles of the contactors.

Rated operational voltage over 3000m :

x 0.9 at 3500m,

x 0.8 at 4000m,

x 0.7 at 4500m,

x 0.6 at 5000m.

Rated operational current over 3000m :

x 0.92 at 3500m

x 0.90 at 4000m

x 0.88 at 4500m

x 0.86 at 5000m

For example, a LC1D80 at 5000m :

- The maximum rated operational voltage is 1000V (IEC 947-4) and 690V (UL/CSA). At 5000m it becomes 1000V x 0.6 = 600V (IEC 947-4) and 690V x 0.6 = 414V (UL/CSA).

- The maximum rated operational AC3 current is 80A at 5000m becomes 80A x 0.86 = 68A.

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