Relays help meet requirements of IEC60204-1

When it comes to designing machinery to meet the requirements of the Machinery Directive (89/392/EEC), one of the key Type B standards used is IEC60204-1:1997.

When it comes to designing machinery to meet the requirements of the Machinery Directive (89/392/EEC), one of the key Type B standards used is IEC60204-1: 1997, Safety of machinery - Electrical equipment of machines - Part 1: General requirements (this standard also exists as BS EN60204-1: 1998).

Typical machinery that is designed to this standard includes metalworking machinery, food machinery, assembly machines, fairground rides, pumps, compressors and power-operated doors (a more comprehensive list is included in Annex A of the standard).

Clearly the standard provides a great deal of information that is useful in the design of safety-related control circuits, but there are certain areas that could easily be overlooked.

Within the introduction to the standard, it is stated that requirements and recommendations are made not only in relation to the safety of personnel and property, but also to consistency of control response and ease of maintenance.

Considering the safety and maintenance aspects together gives an insight into the thinking behind some of Section 7, "Protection of equipment", which contains subsections for overcurrent protection, overload protection of motors, and phase sequence protection.

Common sense says that these areas of a machine's design should be considered, but it is perhaps not always realised that they are covered by the standard - which should be adhered to when designing virtually any machinery that is to be CE marked in accordance with the Machinery Directive.

Section 7.3 of IEC 60204-1 states: "Overload protection of motors shall be provided for each motor rated at more than 0.5kW.

Overload protection of motors can be achieved by the use of devices such as overload protective devices, temperature sensing devices, or current-limiting devices".

More is included in the standard itself, but this extract gives the essence.

Pilz is well known for its safety relays, software-configurable safety controllers and programmable safety systems.

Furthermore, in the wake of recent announcements, the company is gaining a loyal following for its gate switches and emergency stop pushbuttons.

But another area where Pilz can help customers is in the supply of electronic control and monitoring relays, which largely consists of the S-Range of slimline 22.5mm-wide devices.

These enable machine builders to meet the wider obligations laid down by standards such as IEC60204-1.

For example, to comply with the requirements of section 7.3 of this standard, which calls for overload protection of motors, machine builders can install a Pilz thermistor monitoring relay type S1MN, S1M0 or S1MS, or a true power monitoring relay type S1WP.

For each type of device there is a range of models available to suit most application requirements in terms of parameters such as measuring voltage, measuring current and supply voltage.

Section 7.5 of IEC60204-1 states: "Where a supply interruption or a voltage reduction can cause a hazardous condition, damage to the machine, or to the work in progress, undervoltage protection shall be provided (eg to switch off the machine) at a predetermined voltage level".

Again, the standard includes more detail than this.

To meet this requirement, Pilz offers three voltage monitoring relays: S1UM, S3UM and ZUZ.

Various models are available to suit a range of AC and DC voltages, and the S3UM also monitors phase sequence while the ZUZ and S1UM benefit from a facility that allows the reaction time to be adjusted.

Between them, these three types of voltage monitoring relay can meet the needs of most applications.

Section 7.8 of IEC60204-1 states: "Where an incorrect phase sequence of the supply voltage can cause a hazardous condition or damage to the machine, protection shall be provided".

Machinery is most at risk of being subjected to incorrect phase sequencing when it is transferred from one supply to another or if it is mobile machinery that has a facility for connection to an external power supply.

It has already been mentioned that the S3UM device monitors phase sequence in addition to voltage, but Pilz also offers the S1PN phase sequence monitoring relays.

Three alternative models are available to suit different supply voltages and all three feature two auxiliary output contacts and LEDs to indicate "power" and "fault".

Machine builders who require clarification of their obligations under IEC60204-1 are invited to contact Pilz to discuss the machine design and applicable standards.

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