Chapter 7: Electrical Systems
Section 1: Overview
Introduction
Electrical system design involves many considerations. This
chapter covers the areas of special concern to roadway illumination.
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.
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.
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:
- No electrical services present
- Lighting fed directly from electric utility poles
- Conduit installation only, with conductors and light poles to be provided later, or
- 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).
Electrical Details
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:
- ED(1): Conduits & Notes
- ED(2): Conduit Supports
- ED(3): Conductors
- ED(4): Ground Boxes
- ED(5): Service Notes & Data
- ED(6): Service Enclosure & Notes
- ED(7): Service Support Types SF & SP
- ED(8): Typical Traffic Signal System Details
- ED(9): Electrical Service Support Pedestal Service Type PS
- ED(10): Electrical Service Support Types GC, OC, & TP
- ED(11): Duct Cable/Conduit
- ED(12): Battery Box Ground Boxes.