When Cleveland Electric, Atlanta, was hired on a design/build basis as the installing contractor for the renovation project of the William Oliver Building, it embraced the goal of General Contractor Ellis-Don: Save the building owner time and money.
Cleveland Electric's group manager Phil Waagner pursued that goal, noting he not only was responsible for the electrical design, but also for a designthat would keep the project within a tight budget."Since we were closely invol ved in the overall design process, we were able to offer the owner design choices that kept the job within a budget," says Waagner. "We estimate this process saved the owner between $100,000 and $200,000 on the electrical work."
Built in 1930, the 17-story Art Deco-style reinforced concrete structure in downtown Atlanta is on the National Register of Historic Places. Among other restrictions, this meant the contractor had to preserve exterior walls of the office building as well as ensure first floor retail tenants could stay open during restoration.
Facing unique and challenging design factors. Designing and installing a power distribution system that would bring the building up to the prevailing National Electrical Code requirements topped the owner's priority list. More importantly, the design had to fit within tight placement restraints while maintaining power for the first floor retail tenants.
With all-electric appliances, the total load requirement for the 114 loft-style apartments is more than 2500A at 208V (after applying all diversification factors). Power supplies each apartment subpanel at 120V/208V single-phase. A 2500A bus riser system proved to be the normal solution and was Cleveland Electric's first design choice. In this scheme, a plug-in tap appears at every other floor, with a power feeder running from it to a distribution panel. This panel, in turn, feeds apartments on two contiguous floors. However, space problems nixed this design scheme: The 2500A bus duct would not fit through the available floor space within the electrical closets. Also, the 2500A bus riser created Code problems in the electrical closets.
In order to address these problems, Waagner proposed another solution: a hybrid power cable/bus duct system. In this scheme, power to the distribution panels for the first four floors is fed from the main switchboard in the basement with Type MC power cables. Then, a 2000A bus duct starting at the 7th floor and continuing to the top of the building feeds the remaining distribution panelboards.
This lower-ampere capacity busway (and all of the associated components) is less expensive. With its sandwich construction, the 2000A busway is about 9 in. wide and 5 in. deep in cross-section. As a result, it occupies much less space than a multiple conduit riser feeder run.
The Type MC feeder cable simplifies the difficult task of getting power from the basement, through some very tight spots and turns, to the 7th floor. From the main switchgear in the basement, a power feeder consisting of six Type MC cables (each with three 600kcmil aluminum conductors and one 400kcmil aluminum ground) runs to a 2000A tap box on the 7th floor where the busway riser begins. You'll find bus plugs located on the 7th, 8th, 10th, 12th, 14th, and 16th floors and feed distribution panels on the 6th, 8th, 10th, 12th, 14th, and 16th floors.
To serve the 2nd through 5th floor apartments, two Type MC power cables, with three 500kcmil aluminum conductors and one 350kcmil aluminum ground, run from the main switchboard in the basement and feed distribution panels on the 2nd and 4th floors.
Because the hallways above the 1st floor have dropped ceilings, electrical circuits (and air conditioning piping) run in the above-ceiling space. From each electrical closet, a Type MC cable sub feeder (due to tight space restraints) runs to each apartment subpanel.
The owner measures power consumption for each apartment with an electronic system that allows billing from the main office via a telephone modem. Individual apartment data transmits back to a central processor in the main switchgear room. This system gives the owner the ability to add the prorated share of cost of common power usage (such as elevator and lobby lights) to the individual apartment utility bill. Additionally, the owner can buy electrical power at a wholesale rate of about 8 cents/kWh.
On to the wiring. In wiring the apartments, varying in size from a studio to three bedrooms, Cleveland Electric ran Type AC cable within the metal stud walls that form the various rooms and alcoves of each apartment.
All of the apartments have exposed concrete ceilings. As such, a special type of MC cable (MC2) runs to the 31/2-in. octagon outlet boxes that support adjustable accent lighting fixtures and fans. Rectangular in cross-section, the cable's extruded aluminum sheath is the grounding conductor, making it very visually unobtrusive, since it holds the shape and contours to the surface. Once the ceiling is painted, it almost disappears. The sheath-grounding conductor bonds to the outlet box at the box connector, and a grounding conductor pigtail secures to a threaded box screw as the method of providing a grounding conductor attachment to the lighting fixture's grounding conductor.
At the building's interior perimeter walls, wood baseboards hold duplex receptacles at spacings that correspond to NE Code requirements, again using MC2 cable.
The 85,000A available fault current also put a strain on the budget. The high AIC rating meant a higher cost for the main switchboard and its circuit breakers. Using fused switches was out of the question because of the additional equipment space needed. The solution: a combination fused current limiting main bolted pressure switch with distribution circuit breakers.
The emergency generator, which installers had to update to codes, offered numerous challenges. The NEC requires a standby generator provide three times the locked rotor current of the fire pump. Therefore, to match the new 75-hp emergency fire pump requirements, a higher-capacity standby generator than necessary was required for the building emergency loads. By using a 350kW generator coupled with the less expensive 250kW-rated motor, Cleveland Electric met code requirements and stayed within budget.
The only available space for the diesel standby generator is in the basement, where the original coal-fired boiler was located. Cleveland Electric electricians disassembled the generator set and moved it into place in pieces to fit. This was also required to keep below the first floor's weight capacity. The reopened old building center core chimney is used for the generator exhaust, and the long ago abandoned street coal delivery chute is now used as the diesel fuel tank fill point.
The architect was Stang & Newdow, Inc., Atlanta; Brewer & Skala Engineers, Inc., Norcross, GA, handled the mechanical/electrical design.