top of page

Transformers: A Quick Guide

It’s common to have a transformer in a control panel, but what exactly are transformers, how do they work, and what are the different types used in control panels? Let’s have a look at what they actually do 🙂

What Are Transformers?

A transformer in a control panel is used to reduce AC voltage to run a lower voltage on the controls circuit.  Essentially inside it has two coils and the voltage is inducted from the primary coil (input voltage) to the secondary coil (output voltage).  Typically in a control panel that’s to go from 400V or 230V to 24V or 110V.  

How Do Transformers Work?

Transformers operate on the principle of electromagnetic induction. They consist of two main components, primary and secondary windings, which are coils of wire. These coils are wound around a magnetic core, typically made of iron, which helps concentrate the magnetic field.

  1. Electromagnetic Induction: When an alternating current (AC) flows through the primary winding, it generates a magnetic field around the coil.

  2. Magnetic Flux: This magnetic field induces a magnetic flux in the core, which passes through the secondary winding.

  3. Voltage Transformation: The magnetic flux induces a voltage in the secondary winding. The voltage transformation depends on the ratio of turns between the primary and secondary windings. If the secondary winding has more turns than the primary, the voltage is stepped up (increased). Conversely, if the secondary has fewer turns, the voltage is stepped down (decreased).

Fault Finding

There's three main causes of issues with transformers;

a) The wrong terminals - often a transformer will be 'multi tapped', with several configurations of terminals on the primary and/or the secondary side. For example in this photo there are options to connect either 230V, 400V, 415V or 440V on the primary side, and either 12V or 24V on the secondary side. A common mistake is to use the wrong terminals for the voltage required.

b) Overloading the transformer - further details on this below, but make sure the load on the transformer doesn't exceed the rated load.

c) Grounding the 0V - for most applications, 0V on the secondary side of the transformer needs connecting to earth. This prevents issues caused by the secondary voltage 'floating' (which can become quite a high voltage relative to earth), which can be as simple as getting unexpected results which measuring whether or not voltage is present on a specific terminal.

And one more bonus troubleshooting tip - make sure you have voltage on the primary and secondary side of the transformer! If you haven't then it's likely the transformer has failed and needs replacing.

Understanding Transformers: Key Parameters

To select and use transformers effectively, it's important to understand several key parameters:

1. Voltage Rating

The voltage rating indicates the voltage the transformer is designed for on both the primary and secondary windings.

2. Current Rating

The current rating specifies the maximum current the transformer can supply without overloading. Exceeding this rating can damage the transformer and connected devices.

3. Power Rating (VA or kVA)

The power rating, measured in volt-amperes (VA) or kilovolt-amperes (kVA, which is equal to VA x 1000) is approximately equivalent to Watts, so the power rating of the transformer.

4. Turns Ratio

The turns ratio is the ratio of the number of turns in the primary winding to the number in the secondary winding. It determines the voltage transformation characteristics of the transformer.

5. Efficiency

Efficiency measures how well a transformer converts input power to output power. High-efficiency transformers minimize energy loss and heat generation.

To specify a replacement for an existing transformer the crucial parameters are primary & secondary voltages, and power rating. It's also useful to know the size to assess whether the new transformer will fit in place of the old one.

Installation and Maintenance Tips

Proper installation and maintenance of transformers are essential for their longevity and performance:

  • Installation: Ensure transformers are installed in well-ventilated areas to prevent overheating. Follow manufacturer guidelines for mounting and connection to avoid electrical hazards.

  • Maintenance: Regularly inspect transformers for signs of wear, overheating, or damage. Clean and secure connections to maintain efficient operation. Periodically test transformer performance to ensure it meets specified ratings.


Transformers are fundamental components in control panels, providing critical voltage regulation, isolation, and power transformation. Understanding the different types of transformers, their working principles, and key parameters is essential for selecting the right transformer for your application and ensuring safe and efficient electrical power distribution. By following proper installation and maintenance practices, you can enhance the reliability and longevity of your transformers and control systems.


Recent Posts

See All


bottom of page