Principles for using terminal blocks in the Ex area

Explosion protection around the world is mainly based on the IEC 60079 series of international standards and European and American standards and directives. In North America, the basis for this is the National Electrical Code (NEC) in the USA and the Canadian Electrical Code (CEC) in Canada.

Directive 2014/34/EU (formerly ATEX 100a) is of particular importance to manufacturers of devices and protective systems within CENELEC countries of the European Community and beyond. We meet international requirements with IECEx certificates. This means that use in Ex e “increased safety” protection is permitted in Zone 1 and 2.

The principle of “e” increased safety protection (IEC/EN 60079-7) is generally based on increased design measures. The most important ones for terminal blocks are:

• Air clearances and creepage distances
• Terminal blocks must be secured against loosening and they must be fastened and designed so that the cables cannot come loose or be impermissibly damaged by the terminal point.
• The clamping pressure must not be transmitted via insulating parts.
• Terminal blocks that are intended for the connection of multi-stranded conductors must be fitted with an elastic intermediate element.

These requirements and the technical data are checked by an independent testing institute (notified body, e.g., DEKRA, PTB, TÜV, etc.) and certified by the appropriate certificate. The following tests must be verified by the type examination:

• Type test according to IEC 60947-7-1/-2

• Proof of air clearances and creepage distances and dielectric test

• Aging test:

  • 14 days of storage at 95°C and 95% humidity

  • A further 14 days with dry heat at the level of the TI value of the insulation material

  • 24 hours of low-temperature storage at -65°C with subsequent conductor pull-out test

The terminal blocks are therefore approved for installation in Zone 2 and, in particular, Zone 1, i.e., in the actual Ex area. The latter, however, is only on condition that the terminal blocks are installed in connection boxes. The connection boxes must also be approved for Ex e protection and must have at least IP54 protection. The installation instructions, including mounting diagrams, must be followed.

The Phoenix Contact terminal blocks approved for Ex e are standard terminal blocks. They are 100% routine-tested during the manufacturing process in accordance with IEC/EN 60079, which includes a dielectric test.

In the case of terminal blocks from Phoenix Contact, it is therefore not necessary to differentiate between Ex and non-Ex terminal blocks when ordering from stock. The advantages are readily apparent.

No special approval is required for terminal blocks in applications with Ex i intrinsic safety protection. In addition to Ex e approved terminal blocks, standard terminal blocks can also be used here. The increased requirements for air clearances and creepage distances:

• Between adjacent terminal blocks
• Between terminal blocks and grounded metal parts

The distances for rigid insulation are specified in IEC/EN 60079-11 and must be observed. Information regarding the use of Ex i protection can be found in the installation instructions for the terminal blocks for Ex e protection.

In order to be able to measure currents that are above the intrinsically safe range by means of knife disconnect terminal blocks or to protect these currents with standard glass fuses, knife disconnect terminal blocks and fuse terminal blocks with approval for Ex nA protection are available. All elements that can be separated must have a separation force that is greater than 15 N or 100 times their own weight. This will prevent accidental opening. In Zone 2, cartridge fuse-links with sand filling are then used in the fuse holders. The requirements are specified in IEC/EN 60079-15, which will soon be integrated into IEC/EN 60079-7 as Ex “ec”.

Detailed information on terminal blocks in the Ex e and Ex i area is available in the download area for the respective approved terminal blocks.

Here you will find the following:

• Technical data according to IEC/EN 60079
• Approved accessories
• Important installation instructions and mounting diagrams
• Declaration of conformity

However, explosion protection is not just an issue for installers, planners, and operators in traditional systems in the chemical and petrochemical industry. Even in apparently harmless areas of the food industry, for example, there is a significant potential for danger.

This brochure examines the risks in potentially explosive areas. It is intended to help in day-to-day work.