The standard 61439-2 is valid for an altitude up to 2000m. With altitude the atmosphere is modified, cooling efficiency and dielectric properties are impacted.
When installed above 2000m altitude, Prisma P, G and Linergy BS, LGY, LGYE must be derated for the voltage Ui and current.

- The most impact is on voltage (Ui,Ue). As Ui may decrease significantly with the altitude, it must stay valid for the real Ue.
- About the current, the derating should be applied as per the devices altitude derating. (ie: breakers NSX, NW . . .). these deratings are generally given in devices catalogues and may change, depending the ranges.

For Prisma range of products, deratings are:

Altitude	0-2000 m	up to 3000 m	Up to 4000 m	Up to 5000 m
Voltages Ui           k=	1	0.88	0.78	0.68
Current                  k=	As per installed devices altitude derating

More information on the physical phenomena is available in IEC60664 §5.1.2, and “Paschen law” (atmospheric characteristics modified with altitude)

Udgivet til: Schneider Electric Danmark