7 - Protection concept ‘n’

Abstract

This chapter explains the protection concept “n.” The perspective of the user is that Ex “n” is a less-costly approach than intrinsic safety (IS) because no interfaces (e.g., barriers or isolators) are required. It could be argued that the overall installation is less safe with Ex “n” than with Ex “I” with only a marginal cost saving. The use of Ex “n” remains restricted to Zone 2 only. This raises the concern that area classification may be influenced in order to accommodate Ex “n” apparatus. The “non-sparking” concept of protection was originally accepted as safe on the basis of manufacturers using well-designed industrial equipment of good quality and with little or no additional requirements. This is the case when the equipment is operated well within its rating and installed in areas where the risk of contact with a potentially flammable atmosphere is adequately low (Zone 2 only). While the “n” type of protection has common features with the protection “e,” it is in many respects more lenient. For example, in the case of motors one need not specify the lower temperature rises as is done in the case of “e;” also one doesn't require any special overload protection to avoid excessive temperatures under all conditions, including stalling. When selecting the apparatus special care should be taken to ensure that the apparatus and its component parts are constructed to guard against electrical and mechanical failure in the intended conditions of use. Particular attention shall be given to the need for weather proofing and protection against corrosion.