What is Ex nR restricted breathing protection?

What is Ex nR?

Ex nR (restricted breathing) is an ATEX and IECEx protection concept defined in IEC 60079-15. It relies on a sufficiently airtight enclosure to prevent a hazardous atmosphere from entering during normal operating conditions.

The principle is straightforward: if flammable gas cannot get inside the enclosure, it cannot be ignited by the electrical components within. The enclosure is not hermetically sealed, it restricts breathing rather than eliminating it entirely. The standard requires that any hazardous atmosphere present outside is present for less than 10 hours per year in any concentration, which aligns with Zone 2 minimum requirements.

What Ex nR is not suitable for

Ex nR is not suitable for equipment with cyclical operation, for example, components that switch on and off repeatedly. Cyclic operation creates pressure changes inside the enclosure, which act like a pump drawing surrounding air in. This defeats the restricted breathing principle and must be avoided.

Zone 2 and self-certification

Ex nR equipment falls under ATEX Category 3G (Equipment Protection Level Gc). Under IEC 60079-15, category 3 equipment is subject to a manufacturer's self-certification rather than third-party notified body examination, provided the manufacturer can demonstrate compliance through testing.

indEx can provide this self-certification because all indEx enclosures carry a component certificate of II 2GD, Ex e IIC Gb, Ex tb IIIC Db IP66, a higher certification level than required for Ex nR. The ATEX component certificate allows a manufacturer to self-certify for Zone 2 applications once all required tests have been completed.

Stringent tests are carried out to meet the ATEX directive, including heat rise, impact and ingress protection tests. This test data forms the technical file that supports the declaration of conformity.

Why IP66 is essential for Ex nR

The IP66 rating is not simply a water and dust specification for Ex nR enclosures, it is the mechanism of protection itself. The IP66 seal prevents a hazardous atmosphere from entering the enclosure when it is in normal operating conditions.

IP66 is also the most demanding ingress test for an enclosure: it involves powerful water jets directed at the joint areas between lid and base, precisely where any seal compromise would occur. Passing IP66 therefore demonstrates that the gasket joint is sufficiently tight to restrict breathing to safe levels.

indEx silicon gaskets perform at both high and low temperatures and are tested and approved to T3. T6–T4 temperature classes are generally accepted as the norm for enclosures and are compatible with IP66 certification. The gasket must ensure that the normal process of expansion and contraction of the steel enclosure does not allow the seal to be compromised such that a hazardous atmosphere could ingress.

Temperature limits

IEC 60079-15 imposes two temperature requirements that must be demonstrated by test:

• The temperature rise above ambient must not exceed 20 K during normal operation.
• When power is switched off, the rate of temperature fall must not exceed 10 K per hour.

These limits exist because rapid cooling creates a partial vacuum inside the enclosure that can draw in surrounding air. If the fall rate is controlled, the pressure differential remains small enough that the restricted breathing seal prevents ingress of hazardous atmosphere.

Testing is carried out with the enclosure equipped at maximum component density, the configuration the client intends to use. If additional components are added later, the certification becomes invalid.

The three pressure tests

In addition to the heat rise test, one of the following three pressure tests must be completed. The appropriate test depends on the enclosure design:

Test 1, With provision for routine checking

For apparatus that allows periodic checking of its restricted breathing properties. The time interval required for an internal pressure of 500 Pa below atmospheric to change to 150 Pa below atmospheric must be not less than 80 seconds.

Test 2, Without provision for routine checking

For sealed apparatus under constant temperature conditions. The time interval required for an internal pressure of 3 kPa below atmospheric to change to 1.5 kPa below atmospheric must be not less than 3 minutes.

Test 3, Variable volume enclosure (simple pressurisation, Pz)

For enclosures where the nominal internal volume changes with pressure. The enclosure is pressurised with air maintained at an overpressure of 400 Pa. The rate of air supply required to maintain this overpressure is measured. The value divided by the net enclosure volume in litres must not exceed 0.125. This is also known as simple pressurisation or Pz.

The certification process

Where ATEX is applicable, indEx performs the temperature rise and pressure tests on an enclosure equipped with the maximum density of components specified by the client. The components within the enclosure do not themselves need to be ATEX-certified, the primary protection is the restricted breathing enclosure itself.

indEx maintains a full technical file for each project, including all test data and component manufacturers' details, to support the declaration of conformity under the ATEX directive. On completion of testing, a Certificate of Conformity is issued to certify the apparatus to Ex nR. This is charged from £150 and is payable on certificate completion.

Once certified, the client may not install additional components. If the power dissipation within the enclosure increases, the certification becomes invalid, the enclosure may remain safe in practice, but there would be no test data to support that argument.

What we need from you

To provide a quotation and carry out testing, indEx requires the following from the client:

• Full technical data and drawings for all internal components
• The desired internal footprint, including mounting plate size
• Power dissipation of each component in normal operation
• Physical component sizes (height, width, depth)

This data is generally available from component manufacturers on request. Good industrial components are generally acceptable; indEx reserves the right to request an alternative if a component is found to be unacceptable at a later stage.

The testing procedure

1. indEx provides a quotation based on the information supplied.
2. A manufacturer's drawing is produced for client approval (at additional cost).
3. A single sample enclosure is built for each size required, at the unit cost in the quotation.
4. The client installs all components into the sample enclosure.
5. An indEx engineer attends site to complete the required testing. Travel costs are dependent on distance from our facility in Ashford, Kent, and will be advised at quotation stage.
6. The client must be able to wire up and run a dummy load through the complete apparatus. indEx may require the dummy load to run for 24 hours prior to the test engineer's arrival.
7. Once testing is complete, the Certificate of Conformity is issued.

During the testing process, it is theoretically possible for the client to assemble all other required units in parallel, provided the components are exactly the same as those in the type test enclosure.

To discuss an Ex nR project, contact our engineering team directly:

• General enquiries, 01233 801890, [email protected]