Electrical distribution systems are often more complicated than they appear. All distribution equipment and circuits are subject to destructive overcurrents and short-circuits. Determining electrical load requirements and switchgear / panelboard ratings is just a small part of the services we provide for each project. The following is a partial list of items we cover during the course of a typical project.
Power Supply Authority Coordination
For every project that requires a new or upgraded electrical service, we must submit final electrical service arrangement information with loads and anticipated in-service date, using drawings and portions of the specifications dealing with the service entrance.
Primary incoming electrical service configuration
Depending on the type and location of the building or project, the local utility will suggest a specific type of electrical distribution to the site. The most common configurations are radial, primary loop, primary selective, secondary selective, and spot network feeds. It’s also at this point that the determination of overhead or underground service is made with the utility – an overhead service results in cost savings while an underground service increases reliability. Our responsibility is to ensure that your client receives the most economical and reliable system, based on the specific needs of the project.
Ground fault calculation and system capacity
The safety and reliability of your client’s entire electrical distribution system depends on the accurate determination of fault capacity. Once the type of distribution system for the project is finalized, we must coordinate with the local utility to calculate the maximum fault capacity that your client’s incoming distribution system must be capable of withstanding in case of a short-circuit from the utility’s transmission system. The significance of this procedure cannot be over-stated as the health and safety of the building’s occupants is involved. If the distribution equipment is not adequately rated for a ground fault event, the internal switchgear bussing could explode. If the system is over-rated, it represents significant costs for your client. Another important aspect of the distribution arrangement is the proper sizing of the system fusing to ensure that an overload or short-circuit in one portion of the system does not adversely affect the remaining systems. This is also known as selective coordination and is crucial for all distribution systems.
Voltage and phase of system
The correct selection of voltage and phase of the incoming electrical distribution system has a significant impact on the efficiency and cost of your client’s power system. Based on the type and size of building and its power requirements, we select the most cost-effective and efficient voltage distribution. Most mechanical equipment and motors, fluorescent, compact fluorescent, and high intensity discharge lighting can be run from 208volt, 347volt, and 600volt systems. Higher voltages mean smaller wire sizes for a given load and can result in significant savings in wiring installation, depending on their percentage of total building load.
Your client (or his tenants) will be responsible for paying utility bills once power is energized. The metering arrangement will determine how easily that billing is processed. If your client is the only tenant, the solution is simple after minor coordination with the utility. For multi-tenant applications, it may be possible to have direct tenant billing from the utility rather than implementing a check-meter system which adds cost and inconvenience. If a check-meter arrangement is unavoidable, we can design a system that makes collection of power consumption easier and more accurate for your client, based on his budget limitations.
Incoming feeder sizes and termination requirements
Once all of the preliminary calculations and system distribution arrangements are confirmed, the incoming feeder sizes are determined and approved by the local utility. Each utility also has its own standards for feeder terminations depending on the size and type of service. We then must select copper or aluminum as the material for the main feeders, weighing the cost versus capacity features based on the project requirements and budget.
Distribution Equipment Layout
A building that has a proper distribution equipment layout will save your client money and space, while allowing for some flexibility for future electrical capacity.
- Primary and secondary switchboards, and Transformers: The location of primary and secondary switchgear typically depends on the location of the incoming electrical service to the building, to provide easy access for installation and maintenance. By reviewing the building’s load requirements and allowing for anticipated future loads, we provide equipment layouts that minimize dead space.
- Panelboards and Motor Control Centers (MCC’s): Finding convenient spaces for panels and MCC’s is only part of the equation when it comes to locating this equipment. For distribution economics, it’s important to locate this equipment as central as possible to the loads being serviced to reduce voltage drop and to simplify wiring installation. We work with you to determine the best locations for panelboards and other remote distribution equipment.