How are control transformers classified?

Control transformers are classified based on their output capacity, typically expressed in volt-amperes (VA). The classification takes into account both the voltage and the current supplied by the transformer, which together determine its ability to handle electrical load. A transformer rated in VA signifies the maximum output voltage multiplied by the maximum current it can provide.

In practice, this means that when assessing control transformers, professionals need to consider the relationship between voltage, current, and the resulting power delivery. While watts (power) can be used to express load, the VA rating provides a more accurate measure for transformers, especially when dealing with reactive loads encountered in HVAC systems.

Using watts or amperes in classification does not fully account for the electrical characteristics that transformers must manage, particularly in the context of alternating current systems where power factors come into play. Therefore, classifying control transformers in terms of VA—rather than just watts or amperes—ensures that both voltage and current capacity are adequately represented. This is why the classification of control transformers is effectively expressed as watts per volt-amperes, reinforcing the importance of understanding how transformers function in controlling circuits.