FAQs on intrinsic safety

Is there a form for calculating intrinsic safety, for example where you can simply input the values?

The form for establishing proof of intrinsic safety has not been defined. It can be created and stored in written or electronic form. For example, R. STAHL provides a template at (link). Furthermore, R. STAHL offers proof of intrinsic safety as a service. This service is offered in particular for complex interconnections with several sources.

Are Ex i barriers and Ex i transmitters which have only one PTB certificate according to EN 50020 allowed to continue to be operated?

Ex i barriers and Ex i transmitters with a certificate according to EN 50 014 … EN 50 020 (in accordance with EC directive 76/117/EEC) are allowed to continue to be operated. However, it must be ensured that the influence of concentrated capacitances and inductances of the consumer have been taken into account for the verification of intrinsic safety. This means checks should be performed to determine whether the consumer (generally the intrinsically safe equipment) has been certified with a Ci as well as an Li value. In this case, the proof of intrinsic safety must be evaluated in accordance with the requirements of the current version of IEC EN 60079-14 section

Does the EEx i directive still exist?

The EEx marking was used in the past and referred to the underlying European standard (for intrinsic safety, EN 50020) to distinguish it from the American standard AEx, for example. Devices currently being put on the market must comply with the directive 2014/34/EU ATEX. Existing devices, however, may continue to be operated as long as they have been installed in accordance with the current state of the art.

What is better for Zone 2 – the Ex i or Ex e degree of protection?

This question can only be answered with regard to the application. Ex i offers the advantage that the electrical circuit can be separated and connected without having to disconnect the source of electricity or voltage beforehand. For example, this is useful if measurements or a replacement has to be carried out on an electrical circuit.

In Zone 2, the Ex ec type of protection is often used, since here the proof of intrinsic safety is not applicable and installation together with other non-Ex i electrical circuits is easier. However, the disadvantage is that before connecting or disconnecting the electrical circuit, the source of electricity or voltage must be disconnected.

Can I extend the sensor lines between the isolator and sensor with an M12 plug/coupling combination? Does this plug combination have to have ATEX approval?

Plug connectors for Ex i electrical circuits do not need to have approval. They can be assessed as simple apparatus according to the specifications of IEC EN 60079-0, 600079-11 and 60079-14. However, this is only advisable when using plug connectors with one electrical circuit. As soon as more than one intrinsically safe circuit is laid via the plug connector, the plug connector must fulfil the requirements equivalent to that of an Ex e enclosure. It is therefore advisable in these cases to use a plug connector with ATEX approval. There is a new solution from R. STAHL available – the 8595 series miniCON plug connector.

Is an intrinsically safe circuit affected if you clamp with a HART terminal into the current loop for programming/calibration purposes? Does that void the approval for intrinsic safety?

For temporary connection of a HART field communication to an intrinsically safe 4 to 20 mA signal circuit, it must be ensured that the proof of intrinsic safety is observed. If use of such a device is planned, it is recommended to take into account the Ex i parameters for the proof of intrinsic safety.

As such devices have been certified with input as well as output parameters, proof of intrinsic safety with two sources (typically of the associated equipment and the HART communicator) is required before connection to an intrinsically safe circuit. Without a previous inspection, it has not been ensured that the requirements for intrinsic safety have been observed.

Are intrinsically safe and non-intrinsically safe cables allowed to be laid together if both cables are shielded?

Intrinsically safe and non-intrinsically safe cables are allowed to be laid together in a cable duct or on a cable tray if at least one of the two cables is shielded and the shield is earthed.

How great is the minimum distance from intrinsically safe single cores to non-intrinsically safe single cores in the cabinet?

There is no required minimum distance for insulated conductors. However, spatially separated laying is suggested. Here, the principal guideline is that no external energy must be fed into an intrinsically safe circuit.

For the conductive parts such as core end sleeves or clamping points, the minimum distance is 50 mm (tight string length). 

Are equipotential bonding conductors allowed to be laid together with Ex i cables in the duct?

The EN 60079-14 installation standard gives no clear indication here. An equipotential bonding conductor is a non-intrinsically safe circuit, which can temporarily transmit high power. Therefore, an electromagnetic energy transmission cannot be ruled out. For this reason, they must not be laid together.

Cable manufacturers provide the values for C and L for all cable types (core number and cross section). Therefore, is a cable with 2 x 0.75mm² to be treated the same as a 18 x 0.75mm² cable? Are identical values also valid for both cables?

The values specified by the cable manufacturer can be used independently of the core number of the cable.

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