In Roadway Lights and the NEC
The Millennium Edition of the MUTCD, Section
4L.01 has the requirements for In-Roadway Lights (IRL). This type of warning light
is installed in the roadway and is typically used for marked crosswalks. The MUTCD
sets the maximum height of 19mm (0.75 in) above the roadway surface, and has the requirements
for flash rate and actuation method. However the electrical installation method is
up to the agency or Authority Having Jurisdiction (AHJ). The electrical supply can
be in conduit, direct burial, or a saw cut in the pavement, depending on the type
of IRL. Obviously, being able to install the supply conductors in a saw cut is much
less expensive than having to cut the roadway and install conduit. This article will
review the various types of IRL systems and attempt to correlate to NEC requirements.
Types of In-Roadway Lights
There are numerous types of IRL systems, each with different types of lights, power
supply and installation requirements. The three basic types are series, parallel and
inductive. Many of the IRL systems are unique to a specific manufacturer.
- Series AC
Operation: Lamps wired in series (same as an airport runway lighting
system). This equalizes the voltage to each fixture and eliminates voltage drop
Lamp type: Halogen ruggedized airport, 6.6 amp, 7 volts, 50 watts
System voltage: 7 volts per fixture x number of fixtures
Lamp life: 3 years
Conductor: 10 AWG
Typical Installation: RMC or PVC conduit between fixtures.
System voltage is designed for number of lamps, example a six light system has
a operating voltage of 42.
Each fixture has a bypass in case a lamp goes out.
Due to the high brightness of one manufacturers system, it is dimmed to 20% at
- Parallel Low Voltage DC
Operation: Parallel, voltage is increased to compensate for voltage drop
Lamp: high Intensity LED, 1.2 watts
System Voltage: 6 to 32 Vdc
Lamp life: About ten years
Conductor: 16 or 14 AWG, depending on length
Typical installation: Saw cut or conduit, uses a drop in can or a cored hole
- Parallel Low Voltage DC
Lamp Type: High Intensity LED, 2 Watts, 13.5 VDC
System Voltage: 13.5 VDC
Lamp Life: About ten years
Conductor: 14 AWG USE XLP
Typical installation: Saw cut
- Parallel Inductive Powered
Low Voltage DC
Operation: LED lamps are inductively powered from a buried cable. Shuts
off power if cable is cut.
Lamp: High Intensity LED, voltage depends on length of cable, typically is 20
volts for a 24 head installation, 1 amp for 24 head installation
Lamp life: About ten years
Conductor: 8 AWG parallel flat figure 8 cable
Typical installation: Saw cut, using a 2 conductor cable. A node is installed
over the cable, and the node/ cable assembly is sealed. The inductive heads are
epoxyed over the nodes.
What are the NEC Requirements for Installation?
IRL is a relatively new
product, and agencies or the AHJ may not know what NEC rules to use. Normally, the
NEC requirements for a product are determined by its listing/labeling, it is installed
per the instructions and the applicable NEC Article. There are a number of articles
in the NEC that can lead to some basic rules for installing IRL.
For example, Article 411 is Lighting Systems
Operating at 30 Volts or Less. The scope of Article 411 covers lighting systems
operating at 30 volts or less and their associated components. This type of lighting
system is typically used for under cabinet and landscape lighting.
Lighting Systems Operating at 30 Volts or Less. A lighting system consisting of an
isolating power supply operating at 30 volts (42.4 volts peak) or less, under any
load condition, with one or more secondary circuits, each limited to 25 amperes maximum,
supplying luminaires (lighting fixtures) and associated equipment identified for the
Its important to note Article 411
applies to listed lighting systems, meaning a product designed for that purpose, not
one assembled by the user from various components. While Article 411 may not apply
to IRL, the 30 volt or less is an important limitation set by the NEC in
general, as below 30 volts AC is generally not considered to be a shock hazard.
Safety grounding establishes
a low impedance path to the source to remove dangerous voltage due to a ground fault,
to prevent shocks and fires. The rules for grounding are covered in NEC Article 250.
Section 250.20 lists the AC circuits that are required to be grounded:
250.20 Alternating-Current Circuits
and Systems to Be Grounded.
(A) Alternating-Current Circuits of Less Than 50 Volts. Alternating-current circuits
of less than 50 volts shall be grounded under any of the following conditions:
(1) Where supplied by transformers, if the transformer supply system exceeds 150 volts
(2) Where supplied by transformers, if the transformer supply system is ungrounded
(3) Where installed as overhead conductors outside of buildings
AC circuits operating below less than 50
volts are not required to be grounded, except as given above in (1), (2) or (3).
In Article 720 Circuits and Equipment
Operation at Less Than 50 Volts, Section 720.1, Scope states This article covers installations
operation at less than 50 volts, direct current or alternating current. Section 720.10
refers to Article 250 for grounding requirements.
Article 725 does not require grounding
for circuits operating at less than 50 volts per Section 250 112.(I). Generally, grounding
is not required for circuits operating at less than 50 VAC. There are exceptions,
for example: hazardous locations or patient care receptacles. Also, if the IRL lamp
circuit was subject to being energized by a higher voltage than grounding may be required.
Locations subject to lighting may require grounding.
The NEC contains many
references to voltages below 30 VAC being considered safe from contact. For example:
Article 620 Elevators, Dumbwaiters, Escalators, Moving Walks, Wheelchair Lifts,
and Stairway Chair Lifts do not require working clearance for low voltage circuits.
620.5 Working Clearances.
(D) Low Voltage. Uninsulated parts are at a voltage not greater than 30 volts rms,
42 volts peak, or 60 volts dc.
Any voltage can be considered dangerous,
given the right conditions, but generally circuits under 30 VAC RMS and 60 VDC are
safe, and IRL using these voltages or less may be suitable for direct burial or sawcut
Article 725 Class 1, Class 2, and Class 3 Remote-Control,
Signaling, and Power-Limited Circuits
This article can be thought
of as The Mother of All Low Voltage Articles and may be the most appropriate
article for low voltage IRL. The appropriate systems would be:
Class 2 Circuit: 0 to 20 volts, 100 VA, 5 ampere
21 to 30 volts, 100 VA, 3.3 ampere
31 to 150 volts, 0.5 VA, 5 mill ampere
Typical class 2 circuits are thermostat, local area computer networks, and doorbells.
Note as the voltage increases the power limit is decreased.
Class 3 Circuit: Inherently limited 31
to 100 volts, 100 VA
Not inherently limited, 31 to 150 volts, 100 VA
A Class 3 circuit has higher voltage and power limits than Class 2, and the NEC has
additional requirements for safety, as a class 3 circuit can be up to 100 volts, a
A class 2 or 3 circuit does not require
conduit for conductor protection.
Other Than Low Voltage Lighting
If a IRL system is determined
to be other than low voltage, then the NEC rules for power and lighting branch circuits
would apply, in other words the system would be installed much as a standard roadway
lighting system, per Article 240-Overcurrent Protection and Chapter 3-Wiring Methods
- Circuits operating at less than 30
VAC rms and 60 VDC have a reduced shock hazard
- Circuits operating at less than 50
VAC or VDC do not require safety grounding.
- Circuits exposed to lighting (run
overhead) require safety grounding
- Circuits operated from a supply exceeding
150 volts to ground require safety grounding
- Circuits supplied from an ungrounded
supply require safety grounding.
- The usual separation requirements
for low voltage conductors apply (low voltage conductors can not occupy the same
enclosure, box or raceway with power (120 VAC)
- onductors even if insulted for the
maximum circuit voltage (See FPN to 300.3(C)(1) and Section 90.3)
- The type of power supply, and secondary
circuit protection needs to be evaluated. Failure of the power supply could energize
the secondary at the input voltage.
- The installer, manufacturer and AHJ
will determine the installation requirements. Consideration has to be given to
shock hazard, public safety, and maintenance requirements. The most conservative
installation would be rigid metal conduit, with a minimum cover depth of 24
per Table 300.5 PVC conduit can be used, but if exposed to physical damage it
must be Schedule 80 per the UL Listing. An alternative would be to concrete encase
the PVC conduit.
There are many installations
of IRL where the AHJ has required a field evaluation from a testing laboratory, such
as UL prior to approval of the equipment and installation. A field evaluation can
be expensive and delay the project, however the AHJ has the responsibility for approval
of equipment per Section 90.4.
The authority having jurisdiction for enforcement of the Code has
the responsibility for making interpretations of the rules, for deciding on the approval
of equipment and materials, and for granting the special permission contemplated in
a number of the rules.
As these products are not listed by a testing
agency, the AHJ may not allow the installation. The AHJ can only allow approved products
per NEC Section 110.2.
Section 110.3 lists the requirements the
AHJ uses for evaluation of equipment:
110.3 Examination, Identification, Installation, and Use of Equipment.
(A) Examination. In judging equipment, considerations such as the following shall
(1) Suitability for installation and use in conformity with the provisions of this
FPN: Suitability of equipment use may be identified by a description marked on or
provided with a product to identify the suitability of the product for a specific
purpose, environment, or application. Suitability of equipment may be evidenced by
listing or labeling.
The AHJ can allow exceptions, but the new
definition of AHJ in the 2002 NEC refers to Special Permission, and the Article 100
definition of Special Permission requires this to be granted in writing. If a manufacturer
was to offer a listed IRL, it would simplify installation by providing a installation
procedure, and the listing would assure the AHJ the product is safe. Such listing
may provide a market edge.
By special permission, the authority having jurisdiction may waive specific requirements
in this Code or permit alternative methods where it is assured that equivalent objectives
can be achieved by establishing and maintaining effective safety.
Roadway lighting or traffic
signal displays use a standardized lamp, any manufacturers lamp will work in any manufacturers
fixture. IRL must be considered as a system and installed per the manufacturers instructions.
If you are installing a IRL for the first time, after you select the system, review
the installation with your manufacturer and if a permit and inspection is required,
review with your AHJ. The NEC installation requirements are dependant upon the luminare
circuit supply voltage and ampacity. If this is the first application for your agency,
consider getting approval from the AHJ first. Remember a change in the 2002 NEC requires
special permission to be given in writing.
Id like to thank
the following manufacturers who assisted with the technical information on the various
types of IRL systems:
LightGuard, John Kenny
Roland Buehler, Sigma Technologies
Ped-X/Farlight, Bob Tudhope
Traffic Safety/Flightlight, Kyle Owens
This article should not be considered the
final word on NEC requirements for IRL. If you have any comments or installation suggestions
please mail me and Ill do a follow up article later. If there is a manufacturer
of an different IRL system please email me contact information for further follow-up.
Mike Holt's Comment:
If you have any comments on this subject contact the author Tom Baker, Puget Sound
Electrical Training, www.psetraining.com, firstname.lastname@example.org.