When you need to switch transformers in systems — for example, in industrial controls, medical equipment or power converters — switching on the transformer can cause large inrush or switch-on currents. This can lead to safety issues, unnecessary strain and unreliable operation of your installation.
Fortunately, there are special solutions to prevent this: transformer switching relays.
🧠 What is a transformer switching relay?
A transformer switching relay is an electronic relay that can switch on a transformer without causing a large inrush current. This is achieved using a so-called soft start method, in which the transformer is first gently pre-magnetised before being fully switched on.
With conventional switching, inrush currents of more than 80× the rated current can occur. This can:
- cause fuses to blow unnecessarily
- strain power components
- reduce overall reliability
A transformer switching relay effectively avoids this problem.
The TSR family from FSM AG
FSM AG offers a range of high-quality transformer switching relays, each designed for specific applications:
TSRL – Standard model for single-phase transformers
- Soft-switch on method for one or more isolated transformers
- No inrush current, even under load
- Suitable for transformers up to 32 A
- Multiple mains voltage options: 110 V, 230 V, 400 V, 500 V and wide voltage ranges
- Available with or without housing, and with rail mounting options
Other models in the TSR series
TSRLF
This variant works with external switches or thyristors and is suitable for frequent switching or higher loads.
TSR01
Compact electronic relay, ideal for applications with limited space, for example in medical electronics or isolation transformers.
TSRD
Designed for three-phase transformers up to 50 A, with the same soft switch-on technology and reliability.
Why choose soft-switch relay technology?
Transformer switching relays offer numerous advantages:
✅ No inrush current
Thanks to the soft-start procedure, the transformer is slowly brought up to operating voltage without high peak currents.
✅ Greater design freedom
Designers can choose transformers based on performance rather than inrush current limitations.
✅ Improved system safety
Protective measures remain intact and systems are more reliable — especially in industrial and medical applications.
✅ Less maintenance
The absence of current peaks and the soft switch-on method reduce the load on components and extend the service life of your installation.
Areas of application
Transformer switching relays are used in:
- Medical technology, where reliable transformer switching is crucial
- Industrial control systems with frequent switching
- Mechanical engineering and power converters
- Connector and isolation transformers where safety and stability are important
Availability at Isatronick
At Isatronick, we offer various models of FSM AG transformer switching relays in our webshop, ready for fast delivery.
These products combine the proven technology of FSM AG with our local technical support and stock service — ideal for engineers and OEMs looking for reliability and speed.
👉 Discover the complete TSR series and order directly from our webshop
If you are dealing with transformers in your design, a transformer switching relay such as the TSRL, TSRLF, TSR01 or TSRD can make a big difference:
✔ No inrush current peaks
✔ Improved system safety
✔ Less stress on components
At Isatronick, we are happy to help you choose the right model for your application.