Technical Explanations


Unless otherwise required all transformers are dimensioned that the specified assessment output voltage will be attained at the power rating with the efficiency factor cos phi = 1. For three phase current, the rated voltage is the phase-to-phase voltage.


All transformers listed are suitable for use with a rated frequency of 50 – 60 Hz. Double stamp means the same power for both frequencies.

Ambient Temperature

The rated ambient temperature is the maximum temperature the transformers may operate continuously under normal operating conditions. The transformers are rated to a ambient temperature of 40°C. You must consider that they will be attached that the required cooling is warranted, especially inside of housing with higher protection class.

The transformes must be attached that the ducts are vertically aligned. The ducts inlet and outlet must be free of obstructions. For ambient temperature higher than 40°C, the power must be reduced according to the following table.

Ambient Temperature 45° C 50° C 55° C 60° C
Nominal Rating as % of Unit Rating 95 85 80 75

Power-On Time

The nominal rating specification in the catalog refer to the operating mode Continuous Operation (CO). In cases with shorter loading times, Intermittent Operation (IO), mostly a transformer with a lower unit rating can be used.

The transformers power-on time is the percentage of power-on time to duty cycle time. To avoid impermissible temperature rates the duty cycle time must be limited to 10 minutes. The reduction coefficient listed below indicates the permissible transformer size reduction subject to the permanent operation. The time of operation in % can be calculated with the following formula:

Time of Operation % = (Load Time / Duty Cycle Time) x 100%

Time of Operation in % 100 80 70 60 50 40 30 20
Factor 0,95 0,89 0,85 0,77 0,70 0,63 0,55 0,45

Example: rated power is 200 VA, operating time 6 minutes time of operation in % = 6 min. / (6 min. + 4 min.) x 100 % = 60 %

Choice of type: 200 VA x 0,77 = 154 VA required power is 154 VA, type of choice is 160 VA

Please consider that the voltage drop rises in relation of the nominal power to the unit rating.

Installation at High Altitudes (above 1000 m NN)

The transformers, reactors and power supplies are designed for the installation on sites up to 1000 m NN. If the installation site exceeds this altitude the loading must be reduced. The values of power reduction are listed below:

Installation of Altidude in m 1000 1500 2000 3000 4000
power Reducing Factor 1,00 0,97 0,94 0,90 0,85

Protection Type

The protection class labelled as IP XX specifies protection against foreign bodies, contact and water ingress. The definitions of the individual characteristic digits are specified in DIN 40050.


IP 00 no special protection
IP 20 protection against finger contact
protection against penetration by solid foreign bodies larger than 12 mm
IP 23 protection against finger contact
protection against penetration by solid foreign bodies larger than 12 mm
protection against sparkling water falling at an angle of up to 60° to the vertical
IP 54 complete contact protection
protection aginst dust deposits
protection against splash water

IIn the following table, the first an second code digits are listed with designation and explanation of the scope of protection. The IP code numbers can be assembled by means of these datas.

Protection Levels Against Touching, Foreign Bodies and Water

First Digit Protection Against Contact Protection Against Foreign Bodies Second Digit Protection Against Water
0 no special protection no special protection 0 no special protection
1 big body parts big foreign bodies up to 50 mm 1 vertically dripping water
2 fingers or other similar articles medium-sized foreign bodies up to 12 mm 2 angularly dripping water up to 15°
3 wires, tools or objects with thicknesses up to 2.5 mm small foreign bodies up to 2.5 mm 3 angularly spraying water up to 60°
4 wires, tools or objects with thicknesses up to 1 mm small foreign bodies up to 1 mm 4 splash water from all directions
5 dust deposits complete protection against contact 5 jet of water
6 dust penetration (dust proof) complete protection against contact 6 flooding
      7 immersion with pressure and time defined
      8 permanent immersion with defined conditions