The Building

9 - 1 1 R e s e a r c h

an attempt to uncover the truth about September 11th 2001

mirror of “NERDCITIES/GUARDIAN” site : disclaimer

M.I.T., Rotch Visual Collections

Visual Communications in Building Technology Project

....

3.5 THE ELECTRICAL SYSTEM

Electricity is an essential source of power in the normal usage and maintenance of any modern office space. Electrical power is required to drive the air handling units, pumps and chillers of the HVAC system. Electrical power is also utilized as the motive power for the elevators which supply vertical transportation within the office tower. In the following sections it will be seen how electircal power is an integral part of the plumbing and life safety systems. But electricity is not just a source of motive power for the machinery that allows a modern office tower to function, it is also essential in the efficient functioning of any modern business. Today, natural light is seldom an adequate light source and must be supplemented by electrical lights. The very functioning of a business is dependent on such devices as typewriters, copiers, calculators, computers and the essential coffee pot; all of which require electrical power.

The electrical system that supplies all of the diverse needs mentioned above originates from a single utility source. From this central source the power is broken down into many different electrical circuits that must service all of the various needs of the building. This overall transition from the city utility network to office lights and wall receptacles is illustrated in Figure 3.21.

Figure 3.21 PERSPECTIVE OF ELECTRICAL SYSTEM

The electrical power enters the transformer vault located in the southeast corner of the service level. The power enters as a three-phase, 13.2 KVA (kilo-volt-ampere) circuit. A three-phase circuit requires three primary conductor lines sharing a common neutral conductor. Each primary line thus represents one alternating power source 120deg. out of phase with the other two sources. In the transformer vault, the power is stepped down in transformers, (see Figure 3.22) owned by the local utility, to a three-phase 277/480 volts circuit. The nomenclature of 277/480 volt refers to the possibility of connecting two lines to achieve a 480 volt alternating current or a line and the neutral conductor to get a 277 volt alternating current. In the stepped down form, the electrical power passes out of the transformer vault to the main switch gear for Sixty State Street.

Figure 3.22 ELECTRICAL SYSTEMS

.....2.

1. Transformer room.
2. Planter--electricity below.

3. .....4.
3. High voltage transformer.
4. Electrical room.

5. .....6.
5. Power intake--three phases.
6. Water-cooled transformer.

7. .....8.
7. Three phase connections.
8. Transformer cooling coils.

9. .....10.
9. Step-down transformer.
10. Transformer interior.

Two primary feeders become the lowrise and highrise bus risers that supply power to the many office areas of the building. Figure 3.21 diagrams the electrical system in terms of supplying electrical power to a typical highrise floor. As the bus riser passes through the electrical room (see Figure 3.22) for the floor, a circuit is taken off to supply the high power panel (277/480 volts). In the high power panel, additional branch circuits are created. A three-phase circuit is established to drive the air handling unit in the mechanical room (see Figure 3.19). Single phase (277 volt) circuits are established to provide power to the overhead lighting grid for the low brightness fluorescent fixtures. Another circuit is taken off of this high power panel every third floor to be stepped down by a local three-phase transformer to a 120/208 low power circuit.

The switch gear (see Figure 3.22) is located immediately adjacent to the transformer vault. Here the power passes through the necessary meters and circuit breakers as it is broken down into primary circuits. The power then is carried by various feeder buses (see Figure 3.22) out into the structure. Several of these circuits supply power to both the lower and upper (38th and 39th floors) service levels where it is used to drive the motors (for example, see Figure 3.22) of the HVAC, Plumbing and Life Safety systems. Additional feeders also supply the motors of the elevator system.

11. .....12. .....13.
11. Trays for power in and power out. 12. Assembling power trays. 13. High-rise building bus riser.

14. .....15.
14. High-rise building bus riser.
15. Cable trays to building.

16. .....17.
16. High voltage connectors.
17. High voltage cable trays.

18. .....19.
18. Cables in and cables out.
19. Vertical cable riser.

20. .....21. .....22.
20. Transformer -- circuit braker box.
21. Transformer and completed braker box.
22. Transformer and braker box.

23. .....24.
23. Open face braker box.
24. Transformer and boxes.

25. .....26.
25. ?
26. Braker box for fire alarm.

27. .....28.
27. Conduit and junction box in ceiling.
28. Smoke damper in fire wall.

29. .....30.
29. Wire bundle for alarms.
30. Wire bundle awaiting installation.

31. .....32.
31. Flexible conduit with wires.
32. Wiring for light flash diffuser.

33. .....34.
33. Wall outlets.
34. Ceiling with cans and sprinklers.

35. .....36.
35. Sprinklers and ceiling sprinklers.
36. Stacks and floor recepticle.

37. .....38.
37. ?
38. Large ventilation fan and motor.

39. .....40.
39. Elevator equipment.
40. Baseboard heating.

Home
Page