Chapter 7: Electrical SystemsAnchor: #i1005840
Section 1: OverviewAnchor: #i1005846
Electrical system design involves many considerations. This chapter covers the areas of special concern to roadway illumination.Anchor: #i1005857
National Electrical Code
The National Electrical Code (NEC) contains nationally recognized rules for the installation and use of electrical power. The NEC is written by the National Fire Protection Association (NFPA). Each section is written by committees of experts. The purpose of the NEC is the practical safeguarding of persons and property from hazards arising from the use of electricity.
Most local authorities adopt the NEC into law. Although the NEC is not law on state property, TxDOT has adopted it as the standard for electrical installations on State right of way (ROW) to ensure safe operation of electrical systems.Anchor: #i1019636
National Electrical Safety Code
The National Electrical Safety Code (NESC) contains nationally recognized rules for the safe installation, operation, and maintenance of utility electrical power and communication systems. The purpose of the NESC is the practical safeguarding of persons during the installation, operation, or maintenance of electric supply and communication lines and associated equipment. Electric utility providers in Texas are required by state law to follow the NESC.Anchor: #i1019702
NEC, NESC, and Roadway Lighting on TxDOT ROW
TxDOT policy requires that lighting installed on TxDOT ROW be designed and wired according to the NEC (See 2005 memo in Chapter 10). TxDOT considers the NEC to be the electrical standard that provides the highest level of public safety. Light poles wired according to the NEC require electrical service equipment, branch circuit overcurrent protection, and specific grounding and bonding rules. Light poles installed by electric utility providers according to the NESC typically do not have these safety features.
Electric utility providers need permission from TxDOT to install any equipment on TxDOT ROW, and that equipment must be installed according to TxDOT policy. If an electric utility is to be involved in the installation of roadway lighting, it is important to make sure they are aware of the requirement to follow the NEC. Some electric utilities decline to install lighting if the NEC is required.
Engineering consultants and cities are not always aware of TxDOT's NEC policy, and will sometimes submit lighting and electrical plans that have been designed according to the NESC. If any of the following features are present in the plans, the designer should be contacted to ensure the plans submitted conform to the guidelines of the NEC:
- Anchor: #IYAUWXNH
- No electrical services present Anchor: #QDPQNSFH
- Lighting fed directly from electric utility poles Anchor: #RXUUANAN
- Conduit installation only, with conductors and light poles to be provided later, or Anchor: #NOGKARFP
- Plan sheets with electric utility company names in the title block.
For off-system lighting and electrical projects not on TxDOT ROW, but under TxDOT oversight, the work in the project must meet the NEC. However, after the project is finished, the city may install lighting according to the code they choose. In typical projects like this, the conduit will be installed according to the NEC as part of the project. After the TxDOT part of the project is finished, the city may arrange for installation of the conductors and lighting. (See 2008 memo in Chapter 10).Anchor: #i1005885
Current TxDOT electrical specifications are contained in the Electrical Details (ED) Standard Sheets of TxDOT’s Traffic Operations Standard Plans. Information can be found at the following locations:
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- ED(1): Conduits & Notes Anchor: #CRDPFSYW
- ED(2): Conduit Supports Anchor: #NIUDIYCM
- ED(3): Conductors Anchor: #DBICJICH
- ED(4): Ground Boxes Anchor: #WTENNYPO
- ED(5): Service Notes & Data Anchor: #JITLCXMQ
- ED(6): Service Enclosure & Notes Anchor: #KENLOPWS
- ED(7): Service Support Types SF & SP Anchor: #EHLDJFMA
- ED(8): Typical Traffic Signal System Details Anchor: #EDSXPFLC
- ED(9): Electrical Service Support Pedestal Service Type PS Anchor: #IVESHBCW
- ED(10): Electrical Service Support Types GC, OC, & TP Anchor: #OWGJKOTD
- ED(11): Duct Cable/Conduit Anchor: #JQRULIRC
- ED(12): Battery Box Ground Boxes.