Here is the backstory for those of you who are curious:
1981 Code:
A “dedicated space” requirement first appears in Article 384 (Switchboards and Panelboards) It’s numbered 384-2, and says that equipment within the scope of Art 384 “shall be located in rooms or spaces dedicated exclusively to such equipment.” No foreign systems or architectural appurtenances are allowed in these “rooms or spaces” but the dimensions of the space are not defined at all.
There are four exceptions:
1. Control equipment that must be near its machine.
2. HVAC equipment that serves the dedicated “room or space.”
3. Equipment in industrial plants is not required to be in a dedicated “room or space” if it is physically protected from vehicles, accidental contact, or leaks from other systems.
4. Outdoor equipment does not require a dedicated “room or space” if it has a weatherproof enclosure and the physical protection from vehicles, accidental contact, and leaks from other systems.
The substantiation for this proposal was vague – it just said that dedicated equipment rooms used to be the norm, but now large complexes are becoming common and people are running pipes and ducts through equipment rooms, and it would “be safer” not to do that. One of the panel members generally felt that it was good idea, but noted that it was really beyond the scope of Article 384 because it should logically apply to other types of equipment, such as transformers. But, it gets stuck in 384 anyway.
1987 Code:
The dimensions of the dedicated "room or space" are defined as the width and breadth of the equipment, and extending vertically “from the floor to the structural ceiling,” no matter how high that is. Two FPNs are added to clarify that dedicated rooms are not required, and that sprinkler protection for equipment is still permitted in the "room or space."
1993 Code:
The height of the dedicated space is changed to “25 feet or the structural ceiling.” FPNs 3 and 4 are added, clarifying that dropped or suspended ceilings don’t count as “structural ceilings,” and that nothing in this paragraph is meant to allow anything to be installed in the Working Space required by Art 110.
1996 Code:
Section 384-4 is reorganized for clarity but the actual content seems to be the same. There are only two substantive differences I can see – the dedicated space requirement now also applies to motor control centers, and “architectural appurtenances” is no longer on the list of things that cannot be in the dedicated space.
1999 Code:
The Technical Correlating Committee takes 384-4 and moves it into Article 110 to try to group all the “spaces about equipment” requirements in one place. The height of the dedicated space is reduced to “6 feet above the top of the equipment, or to the structural ceiling, whichever is lower.” The exception to the dedicated space requirement is reworded to clarify that equipment can be installed in areas without dedicated space, if that equipment is physically protected from vehicles, accidental contact, and condensation, leaks, or breaks in foreign systems. Also, a separate requirement appears that defines the zone above the dedicated space, and requires leak protection for any foreign systems installed there.
Discussion in the ROPs showed disagreement between committee members about why the dedicated equipment space exists – is it for equipment protection, or for conduit installation? Some argued that allowing conduit installation space protects worker safety. Others argued that conduit installation is a design issue outside the scope of the code, and pointed out that we don’t require conduit installation space on the sides of panels, and also directly accused the rigid conduit manufacturers of trying to influence the code to improve their market share. In this round, the side arguing for the “equipment protection” rationale won the argument, which is why they kept the exception that allowed for zero DES if you have leak protection.
2002 Code:
The exception that basically stated “if you have damage/leak protection, you don’t need dedicated space” is removed. All references to protecting equipment from “vehicles and accidental contact” are removed except the three words in the first sentence, “protected from damage.” The Handbook notes state that “This reserved space permits busways, conduits, raceways, and cables to enter the equipment.”
In this round, the “equipment protection” versus “conduit installation” argument seems to have flipped. The exception was removed based on a proposal that said that the exception contradicted the safe-conduit-installation purpose of DES, and discussed how previous versions of the code had wording that “implied” that equipment protection was the purpose, and that this revision was needed to remove that incorrect implication.
Edit: One interesting thing I noticed is that starting in the late 90s, every proposal related to dedicated equipment space had this same cut-and-paste comment included: "NEMA believes that section 384-4 [DES] is intended to require [dimensions of space] for the installation of conduits, cable trays, etc, entering or exiting the equipment." It appears that NEMA was a significant force in lobbying to get this interpretation adopted, even though the original proposal says nothing abut it.
