Voltages Divided into Classifications
Switching and Distribution Equipment Room
High, medium, and low voltage are the terms we hear the most when talking about voltage classifications. From an international standpoint, these classifications and ranges change depending on where you live. In the United States, the National Electrical Code (NEC) and the National Electrical Manufacturer’s Association (NEMA) have guidelines and standards that cover all voltage classifications. The American National Standards Institute (ANSI) oversees the creation, promulgation, and use of thousands of guidelines and standards that affect businesses. Each industry complies with applicable regulations.
Both the ANSI and the NEC code are publications that are purchased. The Electrical Engineering Portal (EEP) supplies a breakdown of ANSI standards C84.1-1989. This document divides voltages into five classifications. These classifications can be combined into the categories below:
High (HV), Extra-High (EHV) & Ultra-High Voltages (UHV)
- 115,000 to 1,100,000 VAC
Medium Voltage (MV)
- 2,400 to 69,000 VAC
Low Voltage (LV)
- 240 to 600 VAC
Generac issued a white paper titled Medium Voltage On-Site Generation Overview. The white paper compares NEC to ANSI Standards. It cites the following NEC voltage standards:
- High Distribution: 1000 to 4160 volts
- Medium Distribution: 50 to 1000 volts
- Low Distribution: 0 to 49 volts
The above lists illustrate the classification of voltage level changes depending on the governing authority. Generac states that generators less than and equal to 600 volts are medium-voltage and generators greater than 600 volts are considered high voltage. Generators producing 4160 volts are common in many industries for large motors that require high voltage. The backup generator supplies voltage to an individual grid.
Commonly stocked generator voltages are 4160 VAC, 480 VAC, 12,470 VAC, and 13,800 VAC. When power fails to an industrial facility, the backup generator supplies power to distribution and control panels for continued operations. The higher voltages from the generator are stepped down with transformers.
Note:
The content in this document is for informational use only. Always consult with a certified professional when designing and working on electrical equipment. Never work on energized circuits or perform duties that you are not qualified for.
High, Extra-High, and Ultra-High Voltages
High and extra-high voltages are associated with supply transmission from the power plant. The reason for transmitting power at high and extra-high voltage levels is to increase efficiency. The lower current accompanying the high voltage transmission allows for the use of thinner, lighter-weight cables. This reduces the cost in the tower and electrical line construction.
- High Voltages: Range from 115,000 to 230,000 VAC
- Extra-High Voltages: Range from 345,000 to 765,000 VAC
The United States transmits up to 500,000 volts on the high voltage grid. High voltages require specialized switching and distribution panels. The control rooms have redundant switching capabilities. They can be controlled remotely or placed in manual mode for maintenance and testing of individual supply systems. Sub-stations provide stepped-down voltage distributed to localized areas.
Ultra-high voltages are voltages that are over 765,000 to 1,100,000 VAC. China is using the highest voltage transmission at 800,000 VAC. They are developing a 1,100,000 VAC system using cables rated at 1,200,000 VAC today.
Medium Voltages and Industry
Large industrial complexes and factories that require a substantial amount of power often utilize medium supply voltages. Electrical variational analysis dictates that the voltage is inversely proportional to amperage. This means that when the voltage is increased, amperage is decreased to complete the operation.
Motors and electrical equipment designed to operate with higher voltages use less electricity and are more economical to operate. Most primary sub-stations do not receive more than 35,000 VAC from utility supply.
Primary and Secondary Sub-Stations
- Primary Sub-Station: Supplies stepped-down power to secondary sub-stations or single buildings.
- Secondary Sub-Station: Distributes power received from the primary sub-station. They can further step down power for distribution to control panels throughout the facility.
The sub-stations are generally located in areas that can serve one or more buildings on the property.
Example: Aluminum Company of America (ALCOA) Warrick Operations
Located in Southern Indiana, ALCOA generates electricity using a self-contained, coal-fired power plant. They process aluminum ingots into rolled aluminum sheets for factories.
Any factory that uses medium voltage supply to a sub-station requires emergency or backup power supply. Generators that supply 13,800 VAC are common in these settings, supporting continued operations during power outages.
Low Voltage Supply and Controls
Low Voltage Basics
Low voltage has multiple meanings in the electric/electronic world. A common rule of thumb is that anything below 600 volts is considered low voltage. Factories that use automation often utilize multiple voltages.
Supply
Factories requiring medium or high voltage supply often have a dedicated sub-station. However, not all factories require high or medium voltages. Some only require low voltages of 240, 480, or 600 VAC routed directly to the distribution system.
Controls
A system or machine using low voltage to operate higher voltage equipment is the basis for a control system. Programmable Logic Controllers (PLC) are commonplace in these systems.
- Inputs: Received from sensors via the I/O.
- Outputs: Calculated and sent through the I/O, typically 12 or 24 VDC.
The outputs can energize equipment or components via relays. When utility power is lost, the factory shuts down unless properly supported by a backup generator.
Reliable Backup Generators for All Voltage Needs
All factories require power. When utility power is lost, the industry shuts down without a properly sized backup generator.
- We offer a wide range of generator styles to satisfy most needs.
- Pre-owned generators pass a 31-point inspection prior to sales.
- Inventory: Visit our Inventory Page for a list of in-stock generators.
- Generators can often ship within 24 hours of purchase.