Basically ATEX and CNEX are both certificates of Ex but issued by different agent. ATEX is widely considered as an international Ex certificates which would be accepted by oversea countries; CNEX is an EX certificate from local. However according to our project support experiences, not all projects would request international ATEX certificates. It depends on project and client requirements and also depends mostly on budget issue because the cost structure of these certificates are quite different. For more information, please refer to LonTrend Monthly V8.