Electromechanical products

BR930 Q Style and VT1 Relays: Overview

In the digital age, it’s perhaps surprising to learn that considerable investment is still being made in the development, manufacture and testing of relays, which remain a vital piece of infrastructure at the very heart of the majority of the world’s railways.

With track relays first introduced to the rail network as a safety feature in the 1900s, it wasn’t long before the first relay was developed, with the product evolving over the years from the freestanding units of 1910 through to the Q-style relays that are so familiar today. 

The use of relays peaked in the 1980s and 90s, before the development of solid state and computer based interlockings, and they continue to play a key part in railway infrastructure.

With more than a hundred years’ experience in the manufacture of relays in the UK, Siemens Mobility has supplied units to over 95 countries, manufacturing more than two million units for both mainline and metro applications. Projects range significantly in scale, scope and complexity, from single unit replacements to the 13,000 relays supplied in the 1970s to London Bridge - at the time, the world’s largest geographical interlocking.

Siemens Mobility remains the world’s largest supplier of Q-style relays and offers a range of over 430 relay variants, ensuring that in the vast majority of cases, it has a product to meet designers’ precise functional requirements.

Siemens Mobility BR930 Q Style Relays

BR930 Q Style relays offer considerable size and cost saving benefits when compared with the previous large plug-in and shelf type relays. Careful attention to design detail culminated in the production of a safe, dependable and efficient relay, within a standardised, minimum space envelope.

A method of safety interlocking has evolved such that only those units compatible with the plugboard could be mounted. Safety-interlocking with the plugboard is accomplished by the use of pins fitted into holes in the rear of the base moulding and retained by a plate whose fixing screws are protected by tamper-evident seals. Five pins are normally used, and their configuration may be governed by a numerical B.R. Pin Codes, other code series using extra pin position such as S or X. Our Pin Code Index can be found in the link below and will help determine the appropriate relay for your application.


British Rail (now Network Rail) subsequently approved the IRSE designs and published them as a series of B.R. Specifications, starting with B.R.930.  This specified the requirements for a basic dc, neutral, tractive-armature relay; subsequent releases covered varieties such as ac immune and biased types. Please see the glossary of relay types below:

A.C. Immune

A dc relay which will not operate if an ac voltage up to a stated value is applied to the relay coil.


A dc relay which will only operate with one particular polarity of supply. It will not operate if supply polarity is reversed.

Double Wound Coils

A neutral dc relay with two equal independent windings on the coil. Each winding will operate the relay so that relay can be operated from either of two independent sources.

Lamp Proving Relays

A neutral dc relay designed to operate from the current supplied to signal lamps and to release when lamp

or lamps burn out. Some relays incorporate a bridge

rectifier to operate from ac lamp currents.

Magnetically Latched

A dc relay which will only operate with one particular polarity of supply and remains operated when supply is removed. A second winding of the relay coil must be

energised with the correct polarity supply to release the



A dc relay which will operate with either polarity of

supply to the coil.

Sensitive Relay

A neutral relay with high coil resistance and low power consumption.

Slow Acting Relays

A neutral dc relay with a built-in copper slug to delay

the operation or release action (time delay range 0-500ms). Units incorporating various timing methods such as thermal, capacitor/resistor, electronic or synchronous motor (time delay 0-4 minutes).

Track Relay

A neutral relay with low coil resistance and low power consumption.

Train Carried Relays

These relays are a standard design Q type relay with special relay bases to enable them to fit on antivibration resilient mountings.

Twin Relays

A unit having two independent relays, with up to 8

contacts each, all in a standard ‘Q’ type case. Both relays are of the same standard of construction and safety as the single ‘Q’ relays.

Siemens Mobility VT1 Relays

The VT1 relay is designed for use in ac double and single rail resistive or capacitive fed track circuits.  In capacitive fed applications the ‘Control’ winding is made to resonate using an internally mounted capacitor.  This gives the sensitivity and correct phase shift for this application. In resistive fed applications the control winding is unresonated.


The VT1 is a two element ac induction track relay in which a pivoted vane is caused to rotate in a magnetic field. The magnetic field is produced by two elements each consisting of a winding on a laminated iron core. These elements are termed ‘Local’ and ‘Control’. The rotary movement of the vane is converted into linear movement by cranks and links and transmitted to contact assemblies.

Siemens Mobility BR930 Q Style & VT1 Relays Technical Support

Building on a century of experience, Siemens Mobility is able to provide considerable technical support and expertise, offering advice on the most appropriate relay for individual project needs and having the capability to design and manufacture new units for individual projects. With a fast turnaround on enquiries, quotes and manufacture, the lean manufacturing unit provides a modern, efficient and effective support service to customers around the globe.

Relays often operate in challenging yet safety critical environments, so quality and reliability are paramount. Significant investment continues to be made across the manufacturing facility in plant, processes and personnel to guarantee the quality of all equipment. This ensures it can operate just as effectively and reliably in the heat and humidity of Saudi Arabia as the extreme cold of Scandinavia.

Siemens Mobility BR930 Q Style & VT1 Relays Technical Support

To learn more about all of our Siemens Mobility Q Style and VT1 Relays’ technical information, please feel free to check out the data sheets.

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