Increased support from VLT® Soft Starters


The Danfoss VLT® Soft Starter MCD 500 range now supports 690 V on IT earthing systems.

The primary advantage of the combination of 690 V and IT systems is a lower current and limited fault currents. This results in key benefits for the industries where IT earthing systems are used such as Marine and Offshore, Chemical, Mining and Minerals, Metals and Oil and Gas.

The lower current means reduced cable dimensions. This, in turn, implies lower costs, as less copper is needed, and reduced weight, which is important for industries and applications where weight and space is limited (for example, on vessels) and where long motor cables are frequently used (for example, in mines).

Reduced fire risk

Compared to TN systems, the fault currents in IT systems are much lower because, in case of an insulation fault, the current cannot loop via the transformer’s neutral. This ensures that the electrical equipment is subjected to less stress and so its lifetime is extended, optimizing overall maintenance costs.

Fires and explosions can often be started by high local over-heating or by an electric arc due to an insulation fault. The higher the fault current, the greater the risk of fires and explosions. This risk is particularly present in mines, silos and chemical applications and on oil rigs and ships. Due to the lower fault currents in IT systems, the risk of fires and explosions is reduced.

The cost of equipment rated for operation at 690 V and IT systems is generally higher than equipment rated for 380-500 V (TN systems). However, for certain industries and applications, the benefits mentioned above outweigh the higher initial costs.


Illustration 1. The different earthing systems – IT system highlighted


Ideal for a wide range of applications

The applications in 690 V IT system environments where the VLT® Soft Starter MCD 500 is the optimal choice are where the primary requirement is to either move something (for example, water or material/rocks) from one location to another at a constant pace, or setting material in motion in a fixed location (for example, stirring a liquid). These include pumps, fans, compressors, conveyors, agitators/mixers and cranes.

Compared to the Direct On-Line (DOL) or variable frequency converter alternatives, the VLT® Soft Starter MCD 500 offers several features with valuable benefits:


Feature Benefit
Operation of the application with nominal speed with optimum efficiency and zero harmonics Cost savings (TOC)

Long motor cables (up to 500 m) without filtering (both on input and output side)

Only losses during ramping (normally between 5 and 15 sec.) Less heat to dissipate

Low temperature rise inside industrial enclosures

Simple, tried-and-tested technology


Low installation costs

High reliability and availability

Low operation and maintenance costs of the Soft Starter

High power density


Minimum space requirements and low weight
Reduced inrush currents


Harmonize well with high efficiency class motors such as IE3 and in partially IE4

Less wear and tear on equipment lowers maintenance costs of the entire application

Light weight means lower costs

The VLT® Soft Starter MCD 500 is substantially lighter than the equivalent VLT® AutomationDrive FC 302 (see illustration). Its reduced weight has a significant impact on fuel consumption and performance, which makes it the ideal choice for any fixed-speed application on board a vessel.


Illustration 2. Weight comparison VFD vs Soft Starter

Soft starters improve uptime, save energy and effectively protect motors. They are also key to providing you with the freedom to choose the motor control solution that best suits your application.

You can read more about the VLT® Soft Starter MCD 500 here and about other soft starters in the Danfoss Drives portfolio here.

If you have any questions about the Danfoss range of soft starters, don’t hesitate to add a comment below. We’re here to help.

Author: Mikkel Nyhold Bruncke, Global Product Manager, Danfoss Drives

Comments are closed.