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kingtutley (Electrical)
18 Sep 09 14:56
Ok, no dramatic way to ask, so I'll just jump right in.

I have in front of me as I write copies of IEEE C37.20.3 and C37.20.2

Outside of some minor differences in ratings and the rather lengthy definition atributed to MC gear, I can not find a significant difference between the 2. So, is there any truly significant difference here? Is it just a matter of manufacturing quality (ie. MC switchgear is made to a higher standard)? Or have I completely missed the boat?
burnt2x (Electrical)
18 Sep 09 16:44
A metal-enclosed power switchgear is a switchgear assembly completely enclosed at all sides and top by sheet metal (except for ventilation and inspection ports) containing primary power circuit switching and/or interrupting devices with buses and connections and may include control and auxiliary devices. Metal-clad switchgear, by definition, is a specific type of metal-enclosed switchgear.
rbulsara (Electrical)
18 Sep 09 16:51
Somewhat related topic see: thread237-155576: Switchgear versus switchboards

In short, there is a difference in construction and testing standards. And it is significant.

For one metal clad switchgear is not supposed to get deformed due to an internal fault, the metal enclosed one could.

Rafiq Bulsara
http://www.srengineersct.com

jghrist (Electrical)
18 Sep 09 17:14
Metal-clad switchgear has metal barriers between compartments.
alehman (Electrical)
18 Sep 09 17:17
Metal-clad typically has insulated bus. Metal-enclosed does not.

Alan
----
"It's always fun to do the impossible." - Walt Disney

kingtutley (Electrical)
18 Sep 09 18:59
Thank you all for the responses.
Horacemx (Electrical)
27 Sep 09 13:27
Hi, where can I find the construction specs for switchgears more used in US & Canada are they Ansi, NEC or UL???
rbulsara (Electrical)
27 Sep 09 17:03
Horacemx:
For ANSI visit www.ansi.org, for UL www.ul.com

Do you want to build it or specify it?

For specifying ask the mfrs, such as GE, ABB, Square D, Eaton, Siemens or visit their websites. For getting to know what is in the standards you need to purchase them, especially ANSI and UL. UL has some requirements but not all, they are more concerned with testing to the standards claimed by the mfrs, safety and some of their own requirements.

NEC does not have requirement for construction of equipment.

 

Rafiq Bulsara
http://www.srengineersct.com

jraef (Electrical)
27 Sep 09 23:19
My view is that the difference is one of fault tolerance. Not of the gear itself, but of the overall system. With MEIS, a fault in one unit can spread damage to adjacent units, but as long as the damage is contained in the gear, it passes. This means if the equipment being fed / controlled by this gear is interdependent with the other equipment, no big deal because the entire facility must be shut down anyway. If, on the other hand, the equipment being fed / controlled is independent and/or mission critical, Metal Clad gear will contain a fault in one cubicle within that cubical, without affecting adjacent units and therefore the equipment they serve.

So taking that to a practical example, imagine a Pump Lifting Station with 6 big pumps being fed by MEIS gear. A fault happens in one pump and causes significant damage to the controller, which in turn damages adjacent controllers. If the pumps were all necessary for the lifting operation and cannot develop enough head with even one missing, then the fact that one fault took out multiple units is contextually irrelevant. However if these were water supply pumps necessary to maintain pressure that may be needed for fire fighting, having one fault take out multiple units could be disastrous, justifying the use of Metal Clad gear.


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xxjohnh (Electrical)
28 Sep 09 2:26
Metal clad switchgear has each circuit breaker in metal encloser with a seperate encloser for LV controls. Metal enclosed is switchgear components with a sheet metal box around it. Old eastern European switchgear was like that, the main insulation is air. I have not seen any metal enclosed gear for years, except indoor power factor correction equipment. If you get a fault it blows the sides off the sheet metal box.
Most ANSI and IEC switchgear is metalclad.      
alehman (Electrical)
29 Sep 09 21:55
xxjohnh,
We may have different definitions of metalclad switchgear. In the U.S., I think ANSI C37.20.3 metal enclosed gear is much more common than metalclad (because it is less expensive). Metalclad is typically seen where high fault duty, high reliability, frequent operation and/or special controls are needed.

I agree the jraef, except that I would replace "will contain a fault within one cubicle" with "will be more likely to contain a fault within one cubicle".

Alan
----
"It's always fun to do the impossible." - Walt Disney

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