IEC 60204-1: machine safety

In Europe, the Machinery Directive 2006/42/EC and the Low Voltage Directive 2014/35/EU set minimum standards for safety and occupational health requirements. The details and designs for implementation are defined in separate technical specifications, known as harmonising standards.

IEC 60204-1

One of these harmonising standards is IEC 60204-1, which specifies the requirements for the electrical equipment of machines.

It applies to electrical, electronic, and programmable electronic equipment as well as to groups of networked machines, including control cabinet constructions.

Coverage

IEC 60204-1 basically covers devices and components that are operated with nominal voltages up to 1000 VAC or 1500 VDC and with nominal frequencies up to 200 Hz. It covers the complete electrical installation of a machine all the way to the mains cable.

EMC

Chapter 4 of IEC 60204-1 defines electromagnetic compatibility (EMC). EMC immunity and emission tests are mandatory. However, the standard provides for the possibility of waiving certain tests if the electrical components used already fulfil the relevant EMC requirements and the wiring of the components has been carried out in accordance with the manufacturer’s operating instructions. The CE marking of the components basically guarantees that they fulfil the EMC requirements. However, it should be noted here that the components only have to fulfil the EMC limit values of the component standard. And this is not necessarily sufficient to also comply with the application standard. For example, a motor drive meets the EMC requirement for drives, but not necessarily the requirement for machines. It is therefore advisable to carry out an EMC measurement on the finished system.

Mains connection

IEC 60204-1 sets requirements for the mains connection in chapter 5. Part of this is that a disconnecting device must be provided to prevent unexpected start-up. In the event of a mechanical hazard, it is mandatory to provide an emergency stop (chapter 10).

The protective elements are defined in chapter 7. In addition to the necessary overcurrent protection, the use of residual current circuit breakers (RCD = Residual Current Protective Device) is also defined. Accessory sockets on the machine must be equipped with a personal protection RCD max. 30 mA. Please note that RCDs for personal protection must trip at 30 mA earth leakage current but may already trip at 50% of the limit value.

EMC filter

To comply with the required EMC limits, it is advisable to ensure that the machine is designed in accordance with EMC requirements and to use one or more filters. Often, a 1- or 2-stage summation filter at the mains input is sufficient. If this is not sufficient, it usually helps to place filters or filter elements close to the sources of interference — especially the frequency converters. The measure taken must be verified with an EMC measurement. Earth leakage currents should be measured urgently. If these are too high for a mains connection with RCD, an attempt must be made to reduce them. For example, if the inrush leakage currents are too high, the machine can be started up gradually. This effectively reduces the currents to earth and can often be achieved simply by adjusting the control system. Many EMC filters, especially those for motor drives, generate high leakage currents to earth due to their construction with many large capacitors between phases and earth. These filters can be exchanged for low leakage current variants. The use of 4-wire filters with neutral conductor instead of 3-wire filters can also provide a remedy.

If a machine is plugged into the mains, the touchable voltage at the plug pins must be max. 60 V after 1 second. For machines permanently connected to the mains, a discharge time of 5 seconds is sufficient. To comply with the EMC limits, filters with many large capacitors between the phases are often used. These allow a large attenuation of the interference voltage. The problem is that these capacitors store a lot of energy, which is still present when they are disconnected from the mains. It is recommended to select filters with shorter discharge times. In this case, the discharge time of the capacitors is shortened by using leakage resistors with smaller nominal values. This allows a filter’s time of >6 seconds for discharging the residual voltage of 400 V to 60 V within less than two seconds. Some filters even have discharge times of <1 second and are therefore suitable for plug-in connections.

It should be noted that additional capacitors are often installed next to the filter. The entire system must always be evaluated. Therefore, it makes sense to measure the discharge time of the entire system to the required extra-low voltage. For the insulation measurement against earth, it must be noted that in EMC filters resistors are often wired to the capacitors between phases and earth. For the insulation measurement, these should have a resistance value of at least 1 MΩ. Important: It should also be noted here that there may be other resistors between phases and protective earth throughout the installation. It is therefore essential to measure the insulation resistance of the entire system. Machines must also be tested regarding their environmental conditions. This includes vibration, shock, and impact resistance as well as the altitude of the place of use. EMC filters consist of components such as chokes and capacitors, which could be damaged by high vibration levels or mechanical shock. Therefore, filters with a robust design are recommended. For example, filters with partially potted components are much better protected against vibrations. Most filters are qualified for altitudes up to 2000 m.a.s.l. according to the filter standard IEC 60939. For applications at higher altitudes, the extended air and creepage distances according to IEC 60664-1 must be observed.

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