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Master Switch STS

Multi Switch STS Three-Phase
(3:3 100-800 A)

Transfer Systems

Installing a Master Switch static transfer switch provides additional resilience and protection from the disruption that can be caused by the failure of a single power source. The result is the absolute protection of industrial utilities and critical information technology against power supply and load faults.


Technical Specifications

Product Brochures

Operating principle

Master Switch guarantees a source of redundant power, allowing the load to be switched between to alternative and independent power sources.

Switching can be automatic (when a supply source falls outside of acceptable tolerances) or manually done by an operator from the front panel or remotely.

Protection against power supply faults

If one of the two power sources falls outside tolerance levels, Master Switch will transfer the consumers to the second power source (switching is instantaneous if the two sources are in phase).

Protection against environmental disturbances

Overloads and load faults

In the event of an overload, the user can decide the level of intervention of the internal protection devices in order to block the power supply. In the extreme case of a downstream short circuit, Master Switch disconnects the load in order to avoid jeopardising the operation of the other loads (i.e. in the event of poor selectivity of the protection devices).

Total microprocessor control

Microprocessor control logic ensures:

  • Fast and safe switching between power sources
  • Monitoring of all parameters via LCD display
  • Constant monitoring of SCR operation
  • Advanced remote diagnostics (RS232 and TCP/IP).

Redundant design

Power is supplied to the internal logic by two physically separate supply circuits that are fully independent and that can be replaced in “hot replacement” mode without causing power supply interruptions to the load. In the event that the power supplied by both sources fails, full system operation is guaranteed by the “Power Supply back up” function, which provides auxiliary power supply to the circuits from an external, independent power source.

Master Switch is equipped with a dual redundant ventilation system known as: “fan redundance plus”. Thanks to this feature, and in the unlikely event that two fans fail at the same time, those remaining would still be able to dissipate the heat generated at nominal load and with an ambient temperature of up to 40° C. Also the fans can be replaced in “hot replacement” mode, ensuring continuity during the replacement operation.

Superior protection

In the event of an output short circuit, Master Switch blocks the transfer between the two power sources, eliminating the risk of propagating the short circuit and its effects to the other loads. A back feed control circuit ensures the automatic intervention of the protection devices when a return of power to one of the two Master Switch inputs is detected.


The layout of the moving components and parts is designed to ensure easy frontal access:

  • power cable connections that are easily accessed with entry from below
  • boards housed in a dedicated area for rapid diagnosis / replacement
  • all parts subject to monitoring, maintenance and/or replacement.

Advanced communications

Master Switch provides information, measurements, statuses, and alarms via the LCD display. The STS is compatible with PowerShield3 supervision and shutdown software for Windows operating systems 8, 7, Hyper-V, 2012, 2008, and previous versions, Mac OS X, Linux, VMWare ESXi, Citrix XenServer and other Unix operating systems.

MODELS MTS 100 MTS 150 MTS 200 MTS 250 MTS 300 MTS 400 MTS 600 MTS 800
NOMINAL CURRENT 100 A 150 A 200 A 250 A 300 A 400 A 600 A 800 A


Nominal voltage – sources S1/S2 380 – 400 – 415 VAC three-phase + N
Input voltage tolerance 180-264 VAC (selectable)
Switched input phases 3+N (4-pole) – 3 (3-pole)
Nominal frequency 50/60 Hz
Input frequency tolerance


+/-10% (selectable)
Network compatibility IT, TT, TNS, TNC


Transfer type “Break Before Make”
Available transfer methods Automatic / Manual / Remote
Transfer time following source


< 4 msec (S1/S2 synchronised)

10 msec (S1/S2 non synchronised)


Efficiency at full load > 99%
Noise at 1 m from front (from 0 to full load) 55 dBA 55 dBA 55 dBA 55 dBA 55 dBA 55 dBA 57 dBA 62 dBA
Operating temperature 0 °C – 40 °C
Relative humidity 95% non-condensing 5-95% non-condensing
Max. installation height 1000 m at nominal power (-1% power for every 100 m above 1000 m) – Max 4000 m
Reference standard EN 62310-1 (safety) EN 62310-2 (electro-magnetic compatibility)


Weight (kg) 155 160 205 210 235 240 375 560
Dimensions WxDxH (mm) 685 x 530 x 1500 685 x 580 x 1770 950 x 730 x


1250 x 850 x 1905
Color RAL 7016 RAL 7024
IP rating IP 20
Moving the STS Transpallet









Download the Pdf here