I would like to think that this type of installation does technically fall under the general guidelines of the NEC, meaning that a full 36" of front-facing work space must be provided from either side. It's a bit of a gray area though since many AHJ's (Authorities Having Jurisdiction), or inspectors are wishy-washy in how they apply the code requirements.

The NEC also has stipulations regarding pipes, structures, etc. that are mounted above panels, disconnects, transformers or other fixed equipment. It's up to the AHJ to decide if low-voltage equipment in cabinets falls into this category. My guess would be "no" since racks are considered to be portable equipment, as in not a permanent part of the building's electrical system. This would be especially true if all electrical components within the rack are cord and plug connected.

With that being said, a quick call to the electrical inspector's office sounds to be in order. I think that you'll get more of a suggestion from them rather than any level of enforcement. I can't imagine having anything less than 36" of working space anyway, especially if the cabinets involve sliding shelves.

Welcome to the gray area of the NEC. For every requirement, there are usually at least two exceptions elsewhere within the book. I wish I could offer a more definitive answer, but there really isn't one with regard to the NEC. A cabinet or rack is about the equivalent to a refrigerator in the view of the code.

Just remember, nearly every jurisdiction maintains quite a few requirements above and beyond NEC requirements. Local codes always supersede the NEC, so that's why you need to ask this question of the AHJ or code compliance department in your local city, town or county.

Ed Vaughn, MBSWWYPBX