5kV switch in a Class I, Div 2 Area

[edienberg]

I am trying to spec a 600A 5kV fused disconnect switch to be installed in a Class I, Div 2 hazardous area.

The two options I am currently aware of are:

Seal up the enclosure and pressurize it per NFPA 496, since this would be a 4 section switch that is an awful big enclosure to pressurize and monitor for leaks.

Use a gas insulated load break type switch. I don’t know a lot of SF6 but it seams to be the way to go, It just seems a bit pricey.

Any other idea or tips?

 

[davidbeach]

Move the switch outside the hazardous area.

 

[Laplacian]

We use G&W oil filled switches up to 15KV for this purpose; though they are trying to move away from oil based insulation systems. G&W also has the Trident solid dielectric vacuum switch you may contact them about (I don't know if they make one for hazardous locations, but it is totally encapsulated and submersible).

 

[ePOWEReng]

another option is to pipe "clean air" from an unclassified area into switch. Maintain air flowing into the switch and out the open holes.

 

[burnt2x]

edienberg,

Several manufactures make devices that are “factory-sealed” and fit in or on otherwise non-explosionproof boxes, that's an option. Enclosing your equipment maybe the best as far far as safety is concerned. This setup would provide the safety necessary AND remove the need for other seals in the electrical system since the boundary is now the wall.

hold6448, Piping "clean air" is the same as "pressurizing per NFPA 496".

davidbeach, Section 500.4(A)NEC requires the electrical area classification be documented. Since you have to “draw the line” somewhere and it is Division 2, suggest electrical equipment located inside interior walls (enclosed). That would place most of the electrical system outside the classified area.

My $0.02!

 

[davidbeach]

A 5kV fused disconnect that will fit within a wall cavity? That would be a new one, nor do I think that it would convince the AHJ that it was outside the hazard area even if you could find such a beast. I also doubt that you will find a "factory-sealed" 5kV fused disconnect.

 

[rcw retired EE]

Some options-
Change the switch location.

Revisit the area classification and see if the area around the switch can be safely defined as "non-classifed" (Sometimes blanket classifications extending out to the unit boundary limits are more stringent than necessary.)

Elevate the switch and switchgear to the second floor. In refineries with heavier-than-air vapors the classified area may only extend 10-25 feet above grade. An enclosed Power Control Building on stilts is a solution some plants use.

As others have suggested placing the equipment in an enclosure with a pressurized air intake ducted from a safe location (25 feet off the ground) is a common solution.

 

[Laplacian]

I didn't link to it in my first post, but here is such a "beast" as David refers to:

http://www.gwelec.com/product_padmount/Trident_3phase.cfm

 

[davidbeach]

OK, I haven't seen something like that before. It would certainly have to use dead break elbows for hazardous use. Even with the fuses in the elbows it isn't really what the term "fused disconnect" would imply. It doesn't provide the visible air break that a conventional fused disconnect would; if the contact position indicators are enough that might be fine but many safety procedures require a visible air break and that can't be achieved with this without pulling the elbows. Could there be enough trapped charge to cause ignition when the elbows are pulled?

I still say that the best solution is to move the switch, there is certainly a better location.

 

[burnt2x]

davidbeach,

My point is basically to "separate" the equipment from the classified area, not placing the equipment inside a "wall cavity".

The reason I registered to this forum is simply because I know there are other people here who knows more than I do (and vice versa)! Having said that, I take every post well and think it over if these posts/ replies have truth in them! Please go easy on me, will ya?

First and foremost, "respect".

 

[davidbeach]

Nothing personal. I've never seen any indication that any AHJ would say that the wall cavity around a piece of electrical equipment didn't have the same classification as the front of the gear.

Anyone who comes in expecting that others will "go easy on me" is bound to be disappointed. The crew of regulars don't "go easy" on anybody, including the most veteran members. Questions which show that the asker has put effort into trying to determine the answer will be treated with respect and answered with much good information, whether from a first time poster or someone who has been here for years. Statements that fly in the face of long experience can be expected to be received with less than warm hospitality.

Even some members who are now recognized as important contributors had some really lousy newby posts, but they saw how the give and take worked and figured out how to fit in.

As I said, nothing personal. Ask good questions with lots of background and you will get good results. Make statements that aren't well supported and you'll get called on it. Ask questions that resemble a fishing expedition and you won't get much help until you refine the question. All are welcome, but those who "play by the rules" are certainly more welcome.

Enjoy and learn.

 

[edienberg]

Thanks for all the help.

To answer a few questions the switch can not be located outside the hazardous area because we are reworking/refeeding a few existing 4160V-480V transformers that are smack dab in the middle of the plant.

I am still waiting on a price quote from the local G&W rep, but it would appear that the SquareD HVL/cc switch is the way to go. A lineup of 3 HVL/cc switches is a little over half the cost of the conventional HVL switches with a custom purged enclosure.

Thanks again,
Erik


Link to the HVL/cc switch:

http://www.squared.com/us/products/...4EEEF327085256C3D00750075/$file/hvlccswgr.htm

 

[davidbeach]

Are you sure the fuses in the HVL/cc switch are suitable for Class I, Div 2?

 

[ePOWEReng]

burnt2x,

I was referring to a constantly purged box which is different than a pressurized box. I believe an enclosure may be either purged or pressurized per NFPA 496. Maybe I am confused.