Siemens Frequency inverters MICROMASTER – MICROMASTER 420

Frequency inverters MICROMASTER

The MICROMASTERs are a range of frequency inverters for controlling the speed of three phase AC motors. With their default factory settings they cover a large range of simple motor control applications. Via its comprehensive functionality they can also be used for advanced torque control applications.

Siemens MICROMASTER 420 inverter

The MICROMASTER 420 inverter is suitable for a variety of variable-speed drive applications.

It is especially suitable for applications for pumps, fans and conveyor systems.

It is the ideal cost-optimized frequency inverter solution. The inverter is especially characterized by its customer-oriented performance and ease-of-use. Its large supply-voltage range enables it to be used all over the world.



The MICROMASTER 420 has a modular design. The operator panels and communication modules can be easily exchanged without requiring any tools.

Main characteristics
  • Easy, guided start-up
  • Modular construction allows maximum configuration flexibility
  • Three fully programmable isolated digital inputs
  • One scalable analog input (0 V to 10 V) can also be used as a 4th digital input
  • One programmable analog output (0 mA to 20 mA)
  • One programmable relay output
    30 V DC/5 A, resistive load
    250 V AC/2 A, inductive load
  • Low-noise motor operation through high pulse frequency, adjustable (observe derating if necessary)
  • Complete inverter and motor protection
Protection features
  • Overload current 1.5 x rated output current (i.e. 150 % overload capability) for 60 s, cycle time 300 s
  • Overvoltage/undervoltage protection
  • Inverter overtemperature protection
  • Motor protection using PTC via digital input (possible with supplementary circuit)
  • Earth fault protection
  • Short-circuit protection
  • I2motor thermal protection
  • Locked motor protection
  • Stall prevention
  • Parameter interlock

Options (overview)
  • EMC filter, Class A/B
  • LC filter
  • Line commutating chokes
  • Output chokes
  • Gland plates
  • Basic Operator Panel (BOP) for parameterizing the inverter
  • Advanced Operator Panel (AOP) with multi-language plain text display
  • Asian Advanced Operator Panel (AAOP) with Chinese and English plain text dis­play
  • Cyrillic Advanced Operator Panel (CAOP) with Cyrillic, German and English plain text display
  • Communication modules
    • DeviceNet
    • CANopen
  • PC connection sets
  • Mounting kits for installing the operator panels in the control cabinet doors
  • PC start-up programs exe­cutable under Windows 98/NT/2000/XP Professional
  • TIA integration with Drive ES
Mechanical features
  • Modular design
  • Operating temperature: -10 °C to +50 °C (+14 °F to +122 °F)
  • Compact housing as a result of high power density
  • Easy cable connection, mains and motor connections are separated for optimum electromagnetic compatibility
  • Detachable operator panels
  • Screwless control terminals
International standards
  • The MICROMASTER 420 inverter complies with the requirements of the EU low-voltage guideline.
  • The MICROMASTER 420 inverter has the CE marking.
  • Acc. to uL and cucertified
  • c-tick
Performance features
  • Latest IGBT technology
  • Digital microprocessor control
  • Flux current control (FCC) for improved dynamic response and optimized motor control
  • Linear V/f characteristic
  • Quadratic V/f characteristic
  • Multipoint characteristic (programmable V/f characteristic)
  • Flying restart
  • Slip compensation
  • Automatic restart facility following mains failure or fault
  • Internal PI controller for simple process control
  • Programmable acceleration/deceleration, 0 s to 650 s
  • Ramp smoothing
  • Fast current limit (FCL) for trip-free operation
  • Fast, repeatable digital input response time
  • Fine adjustment using a high resolution 10-bit analog input
  • Compound braking for rapid controlled braking
  • Four skip frequencies
  • Removable “Y” capacitor for use on IT systems (with non-grounded mains supplies, the “Y” capacitor must be removed and an output choke installed)

MICROMASTER 420 inverter  Technical specifications

Technical data


Mains voltage and power ranges

200 V to 240 V 1 AC ±10 %

0.12 kW to 3 kW

200 V to 240 V 3 AC ±10 %

0.12 kW to 5.5 kW

380 V to 480 V 3 AC ±10 %

0.37 kW to 11 kW

Power frequency

47 Hz to 63 Hz

Output frequency

0 … 650 Hz, (limitation to 550 Hz in production to comply with legal requirements) 1)

Power factor

≥ 0.95

Inverter efficiency

96 % to 97 % (Further information is available on the Internet at:

Overload capability

Overload current 1.5 x rated output current (i.e. 150 % overload capability) for 60 s, cycle time 300 s

Inrush current

Less than rated input current

Control method

Linear V/f characteristic; quadratic V/f characteristic; multipoint characteristic (programmable V/f characteristic); flux current control (FCC)

Pulse frequency

16 kHz (standard with 230 V 1/3 AC)
4 kHz (standard with 400 V 3 AC)
2 kHz to 16 kHz (in 2 kHz steps)

Fixed frequencies

7, programmable

Skip frequency ranges

4, programmable

Setpoint resolution

0.01 Hz digital
0.01 Hz serial
10 bit analog

Digital inputs

3 fully programmable isolated digital inputs; switchable PNP/NPN

Analog input

1, for setpoint or PI controller (0 V to 10 V, scaleable or for use as 4th digital input)

Relay outputs

1, programmable, 30 V DC/5 A (resistive load); 250 V AC/2 A (inductive load)

Analog output

1, programmable (0 mA to 20 mA)

Serial interfaces

RS-485, optional RS-232

Motor cable lengths

  • without output choke

max. 50 m (shielded)
max. 100 m (unshielded)

  • with output choke

see variant dependent options

Electromagnetic compatibility

Inverter available with internal EMC filter Class A; available as options are EMC filters to EN 55 011, Class A or Class B


DC braking, compound braking

Degree of protection


Operating temperature

–10 °C to +50 °C (+14 °F to +122 °F)

Storage temperature

–40 °C to +70 °C (–40 °F to +158 °F)

Relative humidity

95 % (non-condensing)

Installation altitude

Up to 1000 m above sea level without derating

Standard SCCR
(Short Circuit Current Rating) 2)

100 kA

Protection features for

• Undervoltage

• Overvoltage

• Overload

• Earth faults

• Short circuit

• Stall prevention

• Locked motor protection

• Motor overtemperature

• Inverter overtemperature

• Parameter interlock

Compliance with standards

UL, cUL, CE, c-tick

CE marking

Conformity with low-voltage directive 73/23/EEC

Cooling-air volumetric flow required, dimensions and weights
(without options)

Frame size (FS)

Cooling-air volumetric flow required (l/s)/(CFM)

H x W x D (mm)

Weight, approx. (kg)



173 x 73 x 149




202 x 149 x 172




245 x 185 x 195


Cubic Feet per Minute