Technical information

Definitions of technical terms used on this site.

Rated primary voltage (V)

This is the supply voltage assigned to the transformer by the manufacturer.

Rated secondary voltage (V)

This is the secondary output voltage assigned to the transformer when supplied with the rated primary voltage, frequency range, rated secondary current, all assigned by the manufacturer for the specified operating conditions of the transformer.

Rated power (VA)

The specified power levels in this catalogue are the secondary power levels, in other words, those available when the transformer is loaded. It is the product of the RMS rated secondary voltage by the RMS rated current. If the transformer has more than one output winding, the rated power denotes the maximum sum of the products of RMS rated secondary voltage by the RMS rated secondary current, respectively. This rated power is defined for rated ambient temperature conditions.

example : P = 3,2 VA T70/B

The transformer can deliver 3.2VA at maximum ambient (70°C), the load consisting of a resistor load defined by R(load) = U(sec)_/P (assigned U sec & P values), heating does not exceed the relevant limit for Class B components used in this construction.

NOTE: When the transformer is intended to supply DC voltage and current in conjunction with rectifiers and smoothing capacitors, the VA power required from the transformer is far higher than the U(DC) and I(DC) product. To help you to determine the true transformer power, our Technical Department is at your disposal.

Ambient temperature (ta)

The maximum temperature at which the transformer may be operated continuously under nominal conditions of use. It is the air temperature measured close to the transformer after thermal stabilization when operating at rated conditions.


The increase of the winding temperature when operating at rated conditions and maximum ambient temperature. The heating must be determine by the resistance method.

Temperature class

The international classification of temperature classes is as follows:

A 105°C H 180°C
E 120°C 200 200°C
B 130°C 220 220°C
F 155°C 250 250°C

It defines the maximum temperature the transformer components must withstand in continuous operation, in compliance with the N° 85 IEC publication classification. There insulating materials are therefore certificated for the thermal index corresponding to the declared class in accordance with N° 216 IEC standard.

Particular points of EN 61558-2-6 standard safety transformers

On-load secondary voltage tolerance: This should not differ from the rated value by more than: 10% for transformers with build-in resistance to short-circuits (a supplement of 5% is granted on the 2 nd secondary for tranformers with 2 secondaries).

Off-load secondary voltage: The values given in this catalogue are maximum theoretical values.

Note: For safety transformers, this should never exceed 50 V rms. In the case of a transformer with several secondaries, the sum of the secondary voltages should be less tan 50 V rms

Adapted transformers from the standard series

Any transformer whose requires Power and Ambient corresponding to those of our 44000 & 45000 range, and whose secondary voltage can fit in our minimum to maximum secondary range will be covered by EN61558-2-6,EN60950, or UL506 approvals, depending on the effective choice.

Special transformers

Myrra can use the 44000, 45000 or 46000 standard ranges to examine any transformer for compliance with your specifications and with international standards. On request, we can add thermal protection, thermal fuse thermal switch-CTP. In certain cases, the addition of thermal protection enables the ambient temperature to be increased, while still complying with EN 61558.