Maintenance without Hot Work Permit – Multi Purpose Terminal simplifies installation in Zone 1

The hot work permit, required for many maintenance works in zone 1, e.g. with high-capacity valves, becomes unnecessary using a multi purpose terminal. A 3-stage removal process ensures that any potential sparks remain within the flameproof enclosure.

Often high energy electric circuits also have to be used in Zone 1 explosive environments. In hazardous areas where flammable gases, dust or mists may occur, neither sparks nor hot surfaces must cause an explosion. Electrical devices used in these environments must include protection against this possibility. For electric circuits in measuring and control technology the intrinsic safety type of protection is usually preferred. However, often high energy electric circuits with Ex-e type protection have to be used, e.g. to switch solenoid valves in flameproof enclosures. In the past a hot work permit was required to carry out maintenance work on these electric circuits or the circuits had to be switched off.

The principle

With the new multi function terminal a 3-stage removal process ensures that any potential sparks remain within the flameproof enclosure of the connector.

The red removal lever of the module disconnects the electric circuit.

The metal pins of the module remain in the flameproof cones until after the manual removal of the module.

At this time any potential spark will already have been extinguished and the module is deenergized.

Advantages

The multi functional terminal can be used beneficially for a multitude of tasks. A typical example is to provide fuses for solenoid valves in combination with Remote I/O.

Solenoid valves in flameproof enclosures use a higher drive current than that available with intrinsically safe solenoid valves. However, a powerful valve is particularly important especially for robust applications. In the example shown the high energy valves are switched directly by the Remote I/O via modules connected in Ex-e-type protection.

The Ex-e electric circuits are safeguarded using multi functional terminals and at the same time equipped with a disconnection point which allows the separation of the individual drive circuit for maintenance under explosion-protection conditions without a hot work permit. Figure 4 represents the logical diagram of the electric circuit. The control voltage "V" is fed to the valve via the switch "S" integrated in the Remote I/O. The multi functional terminal "F" is inserted as a safety component. If the safety module is removed, the terminals of the module towards the valve are deenergized and the valve can be replaced without problems. If the fuse triggers because of a short circuit in the valve circuit, the fuse can be replaced by exchanging the safety module.

Versatile application

Besides the use as a safety disconnect terminal the multi function terminal can also be used in a multitude of other applications. The plug-in module has a flameproof enclosure and can therefore be fitted with various electronic components to cover the requirements of the measuring and control technology. Amongst these options are the installation of diodes as OR links as well as the use as coupling relays either designed as a mechanical relay or as an electronic semiconductor relay. Multi function terminals can even be used as bus termination modules for the high power trunk of a PROFIBUS PA or Foundation Fieldbus line.

Summary

Multi function terminals feature modules in a flameproof enclosure within a plug-in base for various tasks in measuring and control technology to make the handling of applications with high energy electric circuits as simple as for intrinsically safe circuits. The special plug-in technology and the multitude of integratable electronic components make this product a very useful element for installations in Zone 1 explosive environments.