NEMA Type 7 Cabinet

[mario8449]

I am currently in the process of figuring out what the best option is for two cabinets that need to be placed in a Class 1 Div 2 location. When examining the option of NEMA Type 7 cabinets, I am concerned about cooling inside the cabinet since putting a fan is not an option. Has anyone encountered this type of issue before?
p.s. These cabinets will be used for DCS remote IO. They will contain processors, DC voltages 24 and 125 VDC, power supplies, and IO cards.

 

[petersonra]

I am currently in the process of figuring out what the best option is for two cabinets that need to be placed in a Class 1 Div 2 location. When examining the option of NEMA Type 7 cabinets, I am concerned about cooling inside the cabinet since putting a fan is not an option. Has anyone encountered this type of issue before?
p.s. These cabinets will be used for DCS remote IO. They will contain processors, DC voltages 24 and 125 VDC, power supplies, and IO cards.

Why are you putting them in XP enclosures in the first place?

Most DCS I/O other than relays are suitable for CID2 areas, and some have hermetically sealed relays that are suitable for such areas.

XP cabinets are usually pretty good conductors of heat from the inside to the outside of the enclosure.

 

[mario8449]

Bob,

The reason I am exploring XP enclosures is because the customer has a priority list for cabinets and XP cabinets comes before purging/pressurization NEMA 4 cabinet in Class 1 Div 2 locations. In other words, if I choose to not use XP cabinets, I must have a good reason, such as a big difference in pricing (which is very possible since I am not even sure I can find big cabinets with NEMA 7 rating). That being said, I wasn't sure what the best way to cool a NEMA 7 cabinet is?

Why are you putting them in XP enclosures in the first place?

Most DCS I/O other than relays are suitable for CID2 areas, and some have hermetically sealed relays that are suitable for such areas.

XP cabinets are usually pretty good conductors of heat from the inside to the outside of the enclosure.

 

[petersonra]

The point is that if you are careful with what you put inside it you won't need to pressurize it nor will it need to be in an XP cabinet.

I have never seen either a fan or an A/C on an XP cabinet. Not saying it can't be done, but I have never seen one.

Best bet is to do the heat calcs and see what the internal and surface temp of the enclosure comes out to. my guess you don't need cooling even if you go with an XP box.

 

[Jraef]

The point is that if you are careful with what you put inside it you won't need to pressurize it nor will it need to be in an XP cabinet.

I have never seen either a fan or an A/C on an XP cabinet. Not saying it can't be done, but I have never seen one.

Best bet is to do the heat calcs and see what the internal and surface temp of the enclosure comes out to. my guess you don't need cooling even if you go with an XP box.

To that goal, a trick of the trade is to reverse engineer the size of the box using the free thermal management software or web sites provided by enclosure mfrs. like Hoffman or Rittal. What you do is gather all of your heat rejection data and determine the highest livable internal temperature, then let the software tell you if you need a fan. If it says you do, keep increasing the box dimensions until is says you no longer need one. That becomes the minimum volume you need to avoid over heating your components.

PS: the only way I've seen to cool a NEMA 7 enclosure is with Vortex Coolers, which require instrument grade compressed air and an approved exhaust system, usually meaning a dedicated pipe to a Non-hazardous area. At that point, the purged system looks better anyway.

Bob's earlier point however was in pointing out that it may be possible to use Cl 1Div 2 DEVICES, so that you don't need a NEMA 7 enclosure for them. For most of what you mentioned, that should not be difficult. The only exception might be whatever is using 125VDC. But if that needs to be switched, could the switching take place remotely and the local system use Cl 1 Div 2 interposing relays?

PS: Vortex coolers can work, but require instrument air too, at which point you may as well go purged.