preferences

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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Just from the perspective of someone trying to install it, which configuration would you prefer and why.

Smallish box (24x24 maybe) with a few instruments and IS barriers, maybe a power supply, and some terminals. Comes assembled and ready to be mounted in a CID1 area. Probably will have a window in the door for viewing the instruments inside.

Would you prefer an XP box or a type 4/12 box with a pressurization/purge unit on it?

In either case all the field wiring from the sensors to the IS barriers in the box is by the field installer including supply of the seals and pouring thereof.

XP box would come with what drilled holes need to be there for bringing in power and going out to the field devices. probably would be (5) 3/4".

If it was a purged system, installer could cut his own holes for outgoing conduit as needed. the purge system would be preconnected and ready for bringing in power and air.
 

rbalex

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Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Oddly enough, in my experience, this preference is rarely my choice for the installation you described; it is most commonly selected by control systems. I'm simply asked to determine if the protection technique is valid. However, if they did consult with me I would not recommend a pressurized protection technique unless it were already the dominant method used in the facility. This is rare today since most facilities have long ago switched from pneumatic to electronic controls.

Purged/pressurized is an active protection technique; explosionproof is passive. When you add up all the mechanical equipment/piping required to deliver clean air/gas and the ancillary loss of pressure detection required, purged/pressurized is rarely an economical choice overall. This is especially true for Type X pressurization which appears to be case for the internal components you described; that is, several of the components wouldn't be suitable in a Division 2, let alone an unclassified location without pressurizing.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Good points.

For something like this the cost is likely about the same for XP versus purged.

Ideally, we could just move the box outside of the hazardous area but for some reason the end user wants it there.

OTOH, it is much easier for us to deal with a purged box over what a long lead XP box that we can't add holes to if it changes after it gets ordered.
 
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