Arc Resistant Switchgear Plenum

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jcook980

jcook980

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Gresham, Oregon
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Electrical Engineer
I'm helping out another engineer who is working with "arc resistant" switchgear that requires an plenum to vent the switchgear outside the electric room. The manufacturer of the switchgear refuses to provide any design guidelines for the construction and installation of the exhaust plenum beyond the flange connecting to their switchgear. He is at a loss as to how to specify the arc exhaust plenum.

All the EE's I've talked to are unfamiliar with this type of switchgear and I had to google a while before finding this paper:

Medium Voltage Metal-Clad Arc Resistant Switchgear

This explains the technology pretty well but doesn't provide much help with the plenum design. A couple of other sites suggest 11 gauge steel with bolted flanges. But no help with plenum size, bracing, etc.

Anyone have experience with installing this type of switchgear?
 
Re: Arc Resistant Switchgear Plenum

Interesting that the gear manufacturer will not help. Page 5 of the link you posted it says "The plenum design must be tested to verify that the potential back pressure does not cause a failure of the arc resistant integrity of the equipment."
 
Re: Arc Resistant Switchgear Plenum

Jim,

The gear manufacturer apparently feels they can not accept the liability of directing the installation of the plenum nor will they provide a plenum if the gear is installed outside of a Power Distribution Center. Odd, since in a PDC the manufacturer would take responsibility for the plenum. What would worry me is using thin gauge duct that could rupture from the discharge pressure rather direct the energy out of the building.

Since the plenum is an unexpected expense, the client is now asking if the switchgear can be directly vented into the electric room!?

Jim

[ January 12, 2006, 03:51 PM: Message edited by: jcook980 ]
 
Re: Arc Resistant Switchgear Plenum

According to the UL White book:
CIRCUIT BREAKERS AND METALCLAD SWITCHGEAR OVER 600 V (DLAH) and CIRCUIT BREAKER SWITCHGEAR, METALENCLOSED, OVER 600 V (DLBK)

"Arc-resistant switchgear has been evaluated for installation in buildings (for indoor applications) that have sufficient overhead space to permit venting without reflecting arc products, as specified in the installation
instructions."
 
Re: Arc Resistant Switchgear Plenum

I wouldn't expect the manufacturer to design a vent pipe for you. Sounds like these are usually installed in a factory that might have 30' of clearance above the equipment.

You need a mechanical engineer to design the vent pipe. In particular, any ME who has done design for the installation of a MRI (Magnetic Resonance Imaging) probably has experience designing pressure relief vents.

(If a MRI suddenly looses power while operating, the liquid helium suddenly boils creating a "quench" that has to be vented outside the building).
 
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