The LEUC supplies the building with medium-voltage power from one or more utility sub-stations. Ideally, the supplies are fed from multiple sub-stations to increase the reliability of the main electrical system. The utility supply will enter the building from below grade and usually terminates in a main switch room. Often, the location of this electrical room depends on the demands of the LEUC.
A significant concern is that each LEUC has its own idiosyncrasies. In some jurisdictions, the LEUC has no requirements for the main switch room at all, and it can be located anywhere within a basement area. In other jurisdictions, the LEUC may require that the main isolation equipment switchgear or ring-main units be located as close as possible to the outside wall where the service enters the building. Other LEUCs, such as the Dubai Electricity and Water Authority DEWA , in the case of Dubai, may demand that this isolation equipment be located in a room at street level, directly accessible from the outside or in a completely separate building at the site property line.
Therefore, it is essential that the electrical engineer contacts the LEUC as early as possible to determine if there are specific requirements for the service entrance equipment and its location.
At this early stage, the engineer also should determine the codes and standards that the LEUC requires for electrical system design. The engineer will likely find that the LEUC has a set of additional design requirements specific to local conditions and local practices.
Often these are not obvious, and if the engineer does not uncover these early, it can be costly to the engineer and to the owner. At a late stage in the design of the Burj Lofts and Burj View buildings in Dubai, DEWA insisted on the addition of a low-voltage main isolation room at the ground level. This change required close cooperation between the engineer and architect to accommodate the room with the least impact on the design and loss of leasable space.
A similar situation occurred during the construction of the Emaar Residential Towers in Dubai. In this case, DEWA changed its high voltage regulations during construction, so that a ground floor ring main unit RMU room had to be added, with a significant impact on the construction process and, once again, loss of leasable space. The medium-voltage supply must be transformed down to the utilization voltage volts in the United States, volts in Canada, and volts or volts in much of Europe and Asia.
In standard buildings, the transformers are located at or below ground level. In extra tall buildings, transformers at low levels are insufficient. At some height, the voltage drop caused by the impedance of the supply conductors will become significant and the supply voltage will fall below acceptable values.
Selecting the location of the service level requires cooperation between the engineer and the architect. The engineer will require the service levels to be located where they can adequately service selected floors. In the Emirates Towers, the transformer rooms at the upper level are located close to the elevator shafts, so that transformers can be transported through the elevator shaft in the event that one must be replaced. Medium-voltage cables must be fed to the transformers on the upper levels.
Frequently, the owner or LEUC will demand that the medium-voltage cables be kept completely separate from any low voltage equipment and routed up the building in separate accessible spaces. The access is necessary so that the cables can be secured and supported at regular intervals so as to relieve stress on the cables, and to limit their movement under short circuit conditions. But what about emergency power? To ensure safety in the event of a normal power outage, emergency power generation is required.
The emergency generators also may be used to provide a reduced level of service to non-critical items. When selecting the generation system, the electrical engineer must decide between low-voltage or medium-voltage generators. Selecting medium-voltage generators allows for the use of fewer, larger generating units, all of which can be located at a low level.
However, a medium-voltage emergency system will require a sophisticated transfer scheme—more costly than low-voltage equipment. In addition, some LEUCs will not permit the use of such an arrangement. Conversely, selecting low-voltage generators will require more generator units. And due to voltage drop, they will have to be distributed throughout the building on service floors. Moreover, electrical and mechanical engineers must coordinate their work to ensure that sufficient combustion air and ventilation is provided to the generator rooms, and to ensure that the exhaust, fuel and cooling systems are correctly designed.
In any building, service rooms and spaces present a design coordination challenge. The architect will strive to maximize the use of space for which the building is being provided and will attempt to minimize the space loss caused by service spaces.
The electrical and mechanical engineers must work closely with the architect to ensure that an adequate number of service rooms and spaces are provided to support the building requirements. They also must ensure that these spaces are large enough and practically located, that is, close to the point of utilization.
The location must allow for easy movement of equipment in and out of the room and to the outside. Finally, the spaces must be configured to accept the equipment they are to house and provide sufficient space for equipment maintenance.
The Code requires that all circuits necessary for the operation of the notification appliances be protected until they enter the evacuation signaling zone that they serve.
Any of the following methods meet the survivability requirements:. Performance alternatives approved by the Authority Having Jurisdiction. Interconnecting wiring to the fire command center control equipment located remotely from the central control equipment must use survivable installation methods for riser circuits to resist attack from a fire.
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The system must assure intelligibility of the voice messages. Any of the following methods meet the survivability requirements: 1. A two-hour rated cable or cable system 2. A two-hour rated enclosure 3.
Fire rated feeder cable is to be used M. Escalator M 2. Dumb Waiter 3. Electric Generator. Ability to take maximum percentage unbalance load R 4. It should also be tested at site.
Telephone Influence Factor R 6. Noise level R 7. Generator Location M 8. C Electric Generator and fire pumps are to be in accordance with the requirement of the Fire Department and it is to be standards. Previous items of checking and testing from Guideline IV which are applicable for external electrical installation 1. Any other items of checking and testing for the external electrical installation 2. Internal Electric Lighting of Building R 1.
Standard service illuminance in lux or lumen per sq. External Electric Lighting of Building R 2. External lighting feeder cable should be protected either by fuses or circuit breakers or earth leakage circuit break ers and in addition every light fitting may be protected individually.
Point by point method of design illumination calculation should be provided as necessary. Measured Illumination Level R 4. All main, secondary and final sub-circuit switch board shall be fitted with mA, mA, mA, 30 mA earth leakage sensitivity circuit breaker respectively to protect the personal equipment PPE from electric shock and electric fire.
Assign competent person to check that every protective device is operating preferable every day before commencement of the work. Indicate clearly the location of switches and alarms which are to be opened or closed in case of emergency e.
Person assigned for the safety of the temporary electrical installations shall maintain the wiring, switches, equipment, etc. Daily report shall be submitted to the Project Engineer. Safety helmet, hand gloves, belt, boots, safety glasses, portable electric fire extin-guisher etc. Safety sign board, danger board and resuscitation diagram together with first aid box shall be kept in a place distinctly known and easily accessible to every worker. In case of any kind of emergency, the contact telephone numbers and addresses, e.
Emergency drill, fire drill shall be exercised periodically as necessary. Work Site if turning out as a hazardous area all electrical installation must be fully aware for safety and necessary protections are to be provided. Lightning Arrester Finial R 1. Typical drawing is shown in Fig. Test Terminal R 3. Earthing Lead R 4. Downtake copper conductor R Separate downtake copper conductor preferably may be used. Lightning Arrester R 7. Aerial Antenner earthing R 8.
Other methods R 9. Earth electrode resistance M Test result as a whole shall not be more than 10 ohms. Regular testing of earthing electrodes M Continuity of lightning arrester path from finials at roof top to earth electrode buried underground shall be checked for possible break, disconnection and poor joints.
Earthing for communication services. Rating of earth resistance shall be less than 1 ohm and as required M. Building lightning arrester system shall be installed to the required safety standard for internal network M. Water Pump motor and others - do - 4. Obstruction Light at Roof Level - do - 5. Fire Protection System Operation and maintenance in general shall be done by consumer; repairs should be done by others. Electric Generator - -do - 9.
Public Address system PA -do - Building Lightning Arrester Operation and maintenance should be done by consumer. Security Door Lock System -do - Commissioning of the above is to be done by authorized person together with installation contractor and the client.
S Cross-sectional area of live conductor. Sp Cross-sectional area of protective conductor.
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