OT: Explosion-Proof Signal Cable

Perhaps I am asking my suppliers the wrong questions, but I need some sort of flexible cable for a 4-wire RS485 application. It is a Class 1 Div 1 environment. It is a short run, and it is hard to justify the expense of isolation barriers. Can anyone make any recommendations?

J E,

if this is a class 1 div 1 environmnent, then you have no choice but to use a barrier. The NAtional electric code (NEC 70) sections 500-5?? defines hazardous installation requirements.

from your safe area, you will need a barrier, then rigid conduit to within 18" of the hazardous wall, a seal, and continue on to the end point in rigid conduit to your device.

the installation requirements should have been spelled out by the engineer classifying the area.

regards,
james

One advantage of Intrinsically Safe implementations in hazardous areas is that the wiring does not have to be EXP.

RS-485 can be made intrinsically safe as evidenced by Profibus DP's use of RS-485.

But all the components of an I/S installation must be certified and transitions from safe to hazardous areas need to an appropriate barrier.

Unless the RS-485 on both ends has a control drawing for I/S, you're stuck with the rules and regs of explosion proof.

501.10(A) allows for other methods besides rigid conduit without requiring a barrier or an intrinsically safe installation for Class I Div 1, notably the use of MC-HL (for power applications) and ITC-HL (for instrument applications). The designation "-HL" refers to Hazardous Location.

You will have to do a cost comparison because the cable glands aren't cheap, but neither is the barrier (we use Stahl Type 9185 Fieldbus Isolating Repeater - around $1500 each).

However, the use of MC-HL and ITC-HL are restricted to use in "industrial establishments with restricted public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation" among other conditions such as using the required listed termination fittings and proper sealing at ALL ends/terminations.

Okonite has an ITC-HL cable made for Fieldbus applications. It is 18AWG and comes in 1 to 24 pairs, so you "may" be able to use a 2-pair for your RS485 depending on what you want the second pair for (for a 4-wire application, or as a power supply to the RS485 device).

I would call Okonite to check on the suitability for RS485 comms for a short run.

http://www.okonite.com/product_catalog/section5/section5-pdfs/5-48.pdf

Crouse-Hinds listed exp sealing gland:
http://www.cooperindustries.com/content/dam/public/crousehinds/Industrial%20EX%20Products/Catalog%20PDFs/Fittings/ADE%206FC%20Armoured%20Barrier%20Gland_North%20American.pdf



PLEASE review NEC 501 in reference to allowed wiring methods (501.10A for CID1), the allowance for using ITC-HL cables, cable sealing, and article 725 by reference.