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I am currently working on a device that is to be used in hostile environments. It needs to be explosion proof. Our team has decided to place our instrument in this housing shown here.

http://www.adalet.com/xdhl-4-id-instrument-enclosure

Now the problem is we have to have the wiring out of that casing. For that there is a blue cap at the top, which can be pulled out and wires can be passed through it.

After wiring is done, we need to fill it with something to contain the explosion.

Anyone has any idea how to make the wiring explosion proof? What wiring to use? What material should the hole be filled with?

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Is the explosive gas, liquid, or solid ? Will there be a pressure difference inside to outside ? Will filling with inert gas do ? How long will it be in that environment ? –  Optionparty Feb 5 at 20:19
    
Google: "explosion proof sealing fitting" –  user28910 Feb 5 at 20:35
    
No liquid or gas. No pressure difference as well. Though the casing my get hot (very hot) due to the instrument being operated. –  Nick Feb 5 at 23:52
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I'm not an expert on hazardous areas. But depending on the temperature the casing reaches, and the explosive gases/dusts present, a temperature as low as 85 C on the external casing may be sufficient to cause an explosion. See for example carbon disulphide gas, which autoignites at 90 C. –  Li-aung Yip Feb 6 at 0:24
    
Electrical explosion proof Piping role ? –  Shireen Agha Faqiree Jul 21 at 7:10

2 Answers 2

up vote 3 down vote accepted

Simple answer is use Ex d (flameproof) or Ex e (increased safety) glands: -

enter image description here

Here's where I found this.

You don't "fill" the hole by the way - an Ex d enclosure has a controlled flame path that restricts the hot gasses leaving and cools them down so they don't detonate gas outside the enclosure. For cables try the same folk: -

enter image description here

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I hear a bit about hazardous area installations at work. Andy is right on the money here - you want an explosion-proof gland. Note the relevant standards are the IEC 60079 series. –  Li-aung Yip Feb 6 at 0:21
    
Also, bear in mind that aluminium (as the link indicates) enclosures cannot be used for coal mining operations if indeed that is your intended "hazardous area" application. Aluminium is an active metal and can initiate a plasmatic arc when struck by iron such as mining vehicle and as such is prohibited. Best to use milled brass. –  Martin Feb 6 at 0:49

Typically, in the United States installations such as this fall under the NEC Electrical Code articles 500 through 517.

The wiring to your enclosure, within the hazardous location, is done using Threaded Rigid Conduit. All fittings that connect to your conduit, including the enclosure you referenced, should have some stamp indicating a rating for hazardous locations (Class 1 Division 1 or 2). they have a range of rated conduit fittings for hazardous locations such as: LB, C, T and Junction boxes. Lengths of Flexible conduits are also available in various lengths. Flexible Conduits have an outer brass braid and have a Hazardous location rating on them.

Within 3 feet of exiting the hazardous area you must use a EY or EXY seal fitting. This keeps any vapors, that may find their way into the conduit, from making their way, through the conduit into a non hazardous location. The inside of the EY Fitting is sealed using Fiber and a Cement like compound. Note the EY or EXY must be rated for the orientation it is installed in (Verticle or Horizontal).

Typically the wiring you use is the same as is used outside the Hazardous location. As long as the Wire is rated for the voltage and what ever physical exposure it may come in contact with (oil, water ect ect).

Beyond making the installation using all rated fittings there are a couple of alternative approaches which give you more flexibility in doing installations with a location such as this:

A.) Interface all the wiring through intrinsic barriers. These are special devices that limit the power delivered into the location minimizing the potential to create an ingnition source

B.) Fresh air purge the enclosure. Systems that use this approach have a purge switch to prove the fresh air purge and will power the equipment down through a contactor if the purge is lost.

These links should help to answer your question on sealing the wiring within the conduit (the EY reference above).

http://www.grainger.com/search?searchQuery=ey+fitting

http://www.grainger.com/product/APPLETON-ELECTRIC-Fiber-Filler-10V102?opr=OAPD&pbi=10V023

http://www.grainger.com/product/APPLETON-ELECTRIC-Sealing-Cement-11K520?opr=OAPD&pbi=10V023

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