How and why are Altistart Softstart de-rated for altitude?

Issue:
How and why is the Altistart 48 de-rated for altitude?

Product Line:
ATS48 ATS22 Altistart Softstarts

Environment:
All

Cause:
Wiring

Resolution:
The lower air pressure results in lower air density and so the cooling is less efficient.
There is also a maximum limit. This is due to the reduced air electrical resistance, which requires larger spacing to prevent arcing. The circuit boards and component spacing allows only a certain altitude and you can’t install it higher.

Maximum Operating Altitude;

3300 ft (1000 m) without de-rating. Above this, de-rate the

nominal current by 2.2% for each additional 330 ft

(100 m) to a maximum of 6600 ft (2000 m)

Released for:Schneider Electric South Africa