The subject of metal-clad versus metal-enclosed switchgear is more complex than this brief reply message can fully explain, however, here is a suggested framework to research the answer. First, the IEEE/ANSI Standards that apply to each of these types of switchgear are very different. There are many ANSI C37 Standards that apply. Historically, this question only concerns medium voltage switchgear in the 5 and 15kV class, as switchgear is used in emergency power systems, such as paralleling generators to serve loads. Several vendors of switchgear, including Eaton Corporation have information in the form of White Papers that they can share that presents the major differences between the switchgear types. One paper by Mr. Bob Gustin, PE, Eaton Corporation, comes to mind as noteworthy, and this paper may be posted on the Eaton Electrical website.
Secondly, vendors are now getting more creative with the ways in which switchgear is designed, thus some modern arrangements and models of switchgear share some characteristics of legacy standards for metal-clad and metal-enclosed switchgear. For example, the MEF class of switchgear from Eaton is a front access only vacuum breaker assembly that uses a vacuum breaker in full compliance with ANSI standards for breakers typically used in metal-clad switchgear, yet packages the breaker into a metal-enclosed assembly. Prior to MEF, Eaton also offered MSB and MEB assemblies that uses fixed and drawout vacuum breakers, respectively, in medum voltage assemblies.
Finally, the two different standards address safety and maintenance from different perspectives. Generally, metal-clad is more robust and would have lower Arc Flash potential in some conditions of maintenance, but that difference is becoming blurred by the newer offereings such as MEF switchgear. Basically, the user should be concerned about the type of switchgear being specified for engine generator paralleling, but the factors of available space, money, electrical switching frequency, electrical protection, arc flash energy, and ease of maintenance all must be separately examined to determine the best solution for a project. Vendors continue to support users and consultants with advice on this matter, and I will be happy to give you further information outside of this forum, especially a local Eaton resource that may be able to assist further in examining the differences between metal-clad and metal -enclosed switchgear.
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