Factors In Selecting A Distribution System

The following is a checklist set up for the evaluation of a system.

1. Safety: The designer must think of the safety to personnel and the safety to the building, materials, and electrical equipment. The designer should never make a compromise where safety is concerned. When the proper equipment is correctly installed and maintained, safety is inherent. In addition, the simpler the system, the safer it is to operate and maintain.

2. Reliability: The degree of reliability which must be designed into the system will be dependent upon the type of building or whether it is a manufacturing or processing plant. In some buildings and plants momentary outages can be tolerated. In other places such as coal mines, machine shops and glass plants, outages are extremely critical. The system should be designed to isolate faults with a minimum of disturbance to the system and should have features to give maximum dependability consistent with the building's requirements.

3. First Cost: First cost should not be the only determining factor in the building or plant wiring design. Minimizing first cost at the expense of reliability, flexibility and satisfactory operation can prove to be very costly.

4. System Voltages, Voltage Variation and Voltage Regulation: Select the proper system voltage for the distances and equipment involved. A study of the system voltage variation and regulation is also important. Voltage variation is defined as the difference in voltage throughout the system at any one time, while voltage regulation is the difference between no-load and full load voltage at any point on the system. Carefully consider the consequence of higher voltages at the source or under light-load conditions that are selected merely to insure adequate voltage throughout the system under loaded conditions. These can cause operating problems.

   As automation, electronics, solid-state devices, etc., move into industrial and commercial applications, regulation and voltage drop become even more important due to the stringent voltage requirements these components place on the system. Voltage regulation on individual equipment may be the most economical solution.

5. Operating and Maintenance Costs: A well-designed distribution system with proper equipment reduces emergency maintenance cost. Plan the system's accessibility and availability for inspection and repairs carefully. Keep the system design simple so that the electricians will have an easier job when and if trouble does occur.

6. Flexibility: Plant loads will probably increase over time. Make allowances for this in the system planning and reflect that in the choice of plant voltages, rating of equipment available, as well as space for additional equipment and capacity. Also consider the ability of the system to accommodate changes of load within the plant. A well-designed system must be flexible.

7. Influence Of Building Construction On Design: The building design also plays an important part in the choosing of a distribution system. Is this an office building? - multi-storied? - single floor? - an industrial plant with high bay, etc.?