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Intrinsically Safe Devices & Control Drawings

I.S. Circuits and Devices

Control Drawing Required: Intrinsically safe devices (both intrinsically safe apparatus and associated apparatus), if intended to be connected to other devices, are provided with a control drawing. A control drawing reference number must be marked on such devices. The control drawing details the requirements for the interconnection of the intrinsically safe device in order to maintain the intrinsically safe protection.

Control Drawing Contents: Control drawings specify the entity parameters used to match intrinsically safe apparatus to associated apparatus suitable to maintain the intrinsically safe circuit protection, and to determine the maximum length of interconnection wiring permitted. The control drawing also includes wiring diagrams to identify each separate intrinsically safe circuit and any permitted combination of separate circuits.

Entity Parameters: Entity parameters is the term for electrical specifications which identify acceptable combinations of intrinsically safe apparatus and associate apparatus that have not been approved as such. For example, an Intrinsically Safe Apparatus will have entity parameters such as maximum current or voltage that can be applied at the apparatus circuit without compromising intrinsic safety. Whereas, an I.S. “Barrier” (associated apparatus) will have entity parameters for the maximum current or voltage that can appear under fault conditions at the apparatus.

Additional Considerations: There are additional installation requirements beyond these most commonly understood requirements. These include:

a) The control drawing for an intrinsically safe apparatus will specify if the apparatus is considered a point of grounding for the intrinsically safe circuit. If this is the case, the associated apparatus must provide isolation from ground to not cause a potential ground loop.

b) The control drawing for an associated apparatus will specify the environment the apparatus can be installed in, but there could be additional requirements based on this environment.

• An apparatus evaluated for installation in a Class I Division 2 location may only be suitable where a supplemental enclosure of a specified ingress protection (ex. IP54) is provided, or where a certain pollution degree can be ensured (ex. Pollution Degree 2).

Summary: While these are only a couple of examples, it is important to review and follow the control drawings for any intrinsically safe installation. Just because the entity parameters match does not mean the intrinsically safe protection is ensured.

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