Low voltage cabling in hazardous areas

[jjjjcarl]

I am designing a system that will monitor points in a Class II Div 1 environment. The system is intrinsically safe and is networked, meaning that all devices are brought to a central field connection box in the classified area and then one Cat 5E cable is run back to the control panel located in a general purpose area. I have been asked to specify a direct-bury Cat5E cable jacket and to run the cable in conduit horizontally to a point near the field connection box, then drop down in open air to the field connection box. The manufacturer maintains that this installation is fine and that the cable does not need to be in conduit. My interpretation of article 250.100 and 502.30 tell me that without the rigid steel conduit connection to the threaded hubs of the field connection box, we are losing the continuity of the grounding connection to that box and therefore this installation would violate the NEC. Who's interpretation correct?

Also, I would like to know if it is OK to run IS rated low voltage cable in open air in classified, (Class II Div 1 and Div 2), areas. Article 502.10 tells me "no", but the equipment manufacturer and on site electrician say "yes".

 

[Smart $]

I am designing a system that will monitor points in a Class II Div 1 environment. The system is intrinsically safe and is networked, meaning that all devices are brought to a central field connection box in the classified area and then one Cat 5E cable is run back to the control panel located in a general purpose area. I have been asked to specify a direct-bury Cat5E cable jacket and to run the cable in conduit horizontally to a point near the field connection box, then drop down in open air to the field connection box. The manufacturer maintains that this installation is fine and that the cable does not need to be in conduit. My interpretation of article 250.100 and 502.30 tell me that without the rigid steel conduit connection to the threaded hubs of the field connection box, we are losing the continuity of the grounding connection to that box and therefore this installation would violate the NEC. Who's interpretation correct?

Need more info to provide an "explicit" opinion. Assuming the box is metallic, bonding methods are not limited to grounding through the run of cat5. If you are referring instead or also to the bonding of the conduit, yes the conduit is required to be bonded.. but here also its bonding is not limited to continuous connection to the field box. Additonally, IS systems can use any Chapter 3 wiring method, which partially answers your next question...

Also, I would like to know if it is OK to run IS rated low voltage cable in open air in classified, (Class II Div 1 and Div 2), areas. Article 502.10 tells me "no", but the equipment manufacturer and on site electrician say "yes".

You need to refer to Article 504 also...



PS: Welcome to the forum

 

[jjjjcarl]

Thanks!

Thanks!

Article 504.20 allows any wiring method suitable for unclassified locations, so the manufacturer and electrician were correct. Thanks for the pointer.

 

[rbalex]

Article 504.20 allows any wiring method suitable for unclassified locations, so the manufacturer and electrician were correct. Thanks for the pointer.

You need to review 504.50 and 504.60. While 504.20 permits any wiring method, grounding and bonding still have very strict requirements in classified locations. This is one reason I ocassionally won't recommend IS for instrumentation systems unless it is the major wiring method for a large operation.

Edit add: For "incidental" installations, grounding and bonding requirements will often be overlooked even if the customary (and otherwise satisfactory)quality is achieved.