I have a question and I don't remember if it was brought up. (Forgive me for getting old) I was at my supply house this weekend and someone was talking about required receptacles and "Usable" wall space. Now I am at work, and my handbook is home. I think there is something in there about that.
Now the question. You walk into a room and there is a 7' bookcase right on the right hand wall. Would you need a floor receptacle to meet the 6' space rule? What about a window seat? Or a home media center with a wall to ceiling video screen?
Harold: IMHO, without getting out the books, wall space is wall space and must conform to the NEC spacing requirements. I don't remember seeing the word 'usable'.
Occasionally, an EC will raise a debate about the wall space behind a door (>24") as to what 'use' a receptacle would be in that space. I see nothing in NEC that exempts that space.
As to the window seats, the required (or design) recept is installed. Bookcases either have the recept at the required spacing (although eventually behind books), or I remember one with a floor recept.
In a situation similar to your bookcase, I've seen rooms with floor-to-ceiling niches that were plainly intended for later insertion of a cabinet. As I see it, there's room to say 'skip the receptacle.'
Or, my personal favorite: the area behind the door. It's one thing to use this area for measurement ... but I've seen a number of situations where the combination of doorways was such that placing a receptacle in that 30" section does nothing but create hazards.
IMO, the problem is not with code and design requirements, but the blind application of 'minimum' code requirements. Simply measuring 12-ft. between receptacles often results in poorly placed receptacles.
While I understand the desires behind this ancient code basic, I think it comes back to the simple fact that you can't legislate good judgement.
With built in book cases it may be best to put the receptacle in the toe kick but that requires coordination between the cabinet builder and the electrician. On Harold's big entertainment center, where is that floor to ceiling TV plugged in?
I would want a quad in an entertainment center and you still may end up with a quasi legal plug strip. It is probably beyond the scope of what they pay for but the user would want a lot of stuff behind his entertainment center if he could get it (in wall chases for cables etc). You certainly want plenty of places to plug things in.
(2) Wall Space. As used in this section, a wall space shall include the following: (1) Any space 600 mm (2 ft) or more in width (including space measured around corners) and unbroken along the floor line by doorways, fireplaces, and similar openings (2) The space occupied by fixed panels in exterior walls, excluding sliding panels (3) The space afforded by fixed room dividers such as freestanding bar-type counters or railings
A built in, floor to wherever bookcase creates a break in the wall space at the floor line, it doesn't continue it. Keep in mind that we are talking about minimum required receptacles, not the extra stuff for an entertainment center or video wall that a homeowner or builder might ask for IN ADDITION to the minimum. If the builder wants a receptacle in the bookcase, fine. But it's not required in the case described by the OP.
One of the McMansions has a library, custom floor to ceiling bookcases and one door and one window. Cases are cherry, extreemly detailed. Room has duplexes cut into the mullions that are 5" wide. Duplex every 4'; 12" AFF.
The receptacles under the window seats are in the toe kicks. The home theater had a duplex for the ceiling mounted projector, and 3 pcs of six foot, 6" OC plugmold at the equipment rack location. Theater room had code recept spacing.
This GC has a steady EC & Plumbing sub, and all the rest of the tradesmen are his direct employees, which creates cooperation!!!