Introduction to Intrinsically Safe Radios

Locations and Labels

Labeling – the numbers and letters on the back of the radio

Certification is carried out by approved bodies, who may be registered under multiple systems.

  • In North America these are Nationally Recognized Testing Laboratories (NRTLs).
  • In Europe the laboratories are Notified Bodies under the ATEX scheme.  Under the IECEx system they are Certification Bodies (ExCB).
  • In Brazil the laboratories are accredited by INMETRO.

All IS certified electrical equipment will carry a label specifying the exact IS rating, along with a reference to the particular body that certified it.  In the image to the right, the red boxes highlight the important IS markings.

In addition to the marking examples below, there will be additional markings, including certificate details, model and serial number. The Equipment Protection Level (EPL, Gb for gas or Db for dust) may also be appended.

A further point to check is whether there is an ‘X’ after the Ex certificate number. This indicates special conditions that must be observed, which will be explained in the user manual.

IECEx Markings

Below are two examples of IECEx IS markings, or ‘Ex’ marking. The details of the marking are explained below the marking.

IECEX Markings

For countries that accept IECEx directly, such as Australia and New Zealand, there is no additional compliance marking, as there is for ATEX.

ATEX Marking

North American Marking

With the addition of zones to CEC and NEC, Canada and the US now have both division and zone markings. Not all US jurisdictions have adopted the newer versions of the NEC.


Example of equipment marking for Intrinsic Safety for gas and dust:

Division Markings


The CEC/NEC zone-based marking is very similar to the IECEx marking, but prefixed with A (“AEx”). The class is still marked and Zone replaces Division. For example:

North American Zone

Next we will learn how to use the information on labels to determine if you are using the right device in the right area.