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python01

Controls for hazardous zone area and safety relay

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I have a question regarding hazardous zone design. My control cabinet will be in safe area but I need to have e-stop and safety limit switch located in hazardous area, Div 1 Zone 1. I am assuming that I can use zener barriers or isolators between the field devices and safety relay. I just wonder if the safety relay will function properly with barriers in between? Also do I have to use 24VDC safety relay for this application? I don't know what voltage/current is present on the terminals connecting to safety devices.

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If you use a conduit listed in NEC Article 501 and the E-Stop housing is listed for hazardous locations, then you can take the 24vdc (or 120vac) straight to the device. Another way: you can use an intrinsically safe barrier inside your enclosure, and take the IS wiring to your E-Stop. Doing this will not affect the E-Stop Sensitivity Relay at all. Just make sure you use N/C monitored contacts on your E-Stop, a N/O contact on your IS Barrier (which will be energized under regular conditions thus making the contact close) and the standard SIL 2/3 wiring diagrams on the E-Stop relay. I recommend Phoenix Contact P/N 2865434 for the IS Barrier.

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After pricing some explosion proof operator consoles I think I will be much better off just using intrinsically safe barriers. Do I have to run intrinsically safe wiring in separate conduit separate from the other wiring? And should the conduit be blue?

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Yes, all IS wiring shall be no less than 2 inches from non IS wiring. The conduit does not need to be blue, but identifiers within the panel should be. I.e. Terminal Blocks, wiring, and wire-way.

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Thanks for the great info. I really appreciate you took time to help me out.

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I don't know what you're looking for when you say "explosion proof operator console", but it sounds expensive. Aren't you just looking for a single E-Stop button? You can just get a regular explosion proof box with an E-Stop button (like this). Then make sure you either have a conduit seal or a sealed Tek connector (STX) if you are using Tek Cable. I'm not saying it's better or worse, but then you don't have to create a physically isolated part of your cabinet for intrinsically safe installations, and a dedicated intrinsically safe conduit/cable tray, and all that stuff that comes along with intrinsically safe installations. Edited by MrAutomation

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