March/April 2021 | Vol. 26 No. 2
by Dan Evans, Senior Director of Product Management, Itron, Inc.
Mr. Evans has more than 25 years of experience in the networking and computer industries with a strong focus on wireline and wireless data services/equipment, including pioneering work in broadband internet and large-scale IPv6 networks.
As more and more cities and utilities embark on upgrading their lighting infrastructure to light-emitting diodes (LEDs), a critical decision that may be easily overlooked is which type of receptacle (or socket) they specify to be used for lighting controls. The lighting manufacturers offer a myriad of options, but which one is best to lay a solid foundation for expanding from simple lighting controls to electronic methods and sensors (or “smart lighting”)? Which ones are better to use the insight gained from that data as “smart cities,” and beyond? This article will help explain some key differences between two common sockets from two global Standards organizations: the ANSI C136.41 socket and the Zhaga Book 18 socket.
In 1979, the ANSI C136.10 Standard was ratified. This Standard specified a three-pin physical interface for twist lock controls for photocontrols used on public and private lighting fixtures. In 2013, the Standard was enhanced to include four new (low-voltage) pins for dimming controls and future services. This new Standard is defined in the ANSI C136.41 Standard. Given the NEMA role in the Standards groups, the industry came to refer to the ANSI C136.41 receptacle as the “seven-pin NEMA socket.” Dimming was the primary new use case and allocated pins four and five; the future services that might utilize pins six and seven are currently under development in the Standard revision.
Europe has traditionally not used external controllers on individual luminaires (lighting fixtures). Instead, there was a combination of cabinet controllers and internal controllers. In 2019, the Zhaga Consortium expanded Book 18 “to create an interoperable system of an outdoor luminaire and sensing/communication modules.” The goal was to create an ecosystem of interoperable products from luminaire suppliers and sensor suppliers. Unlike the ANSI Standard, this specification was based on four low-voltage connections and dc power. This new Standard interface was designed to be used for sensors that enable lighting controls, but also with connected cities’ sensors in mind.
There are three pins for mains power and four pins are for low-voltage signaling.
Note: ANSI C136.41 is currently under revision and includes a table of multiple use cases.
ZHAGA BOOK 18
There are four pins for low-voltage signaling.
The primary use of the ANSI C136.41 socket is for controlling when an outdoor light goes on and off. This started with the original three-pin version (ANSI C136.10) with a simple photocell sensor plugged in. When inserted properly in the receptacle, the photocell would use an internal photo-optical sensor to measure ambient light levels around the light fixture. At dusk/sunset, when the ambient light drops below a “darkness” threshold at dusk/sunset, the photocell closes an onboard relay that energizes the lamp. Similarly, at dawn/sunrise, the photocell would open the relay once ambient light was above the threshold. When the lamp was on, it was on at full brightness (for some lamp technologies, it took a few minutes to get there).
As continuously dimmable LED fixtures became more cost-effective, this type of fixture drove the introduction and adoption of the five-pin and seven- pin version of the socket (ANSI C136.41). When combined with a “smart photocell,” that receives and responds to a signal, the LED fixture (and internal LED driver) would support the use case of dimming the lamp to some value less than 100 percent brightness. This dimming feature was useful for situations where the LED fixture provided more light than needed or in cases where additional energy savings was desirable.
Currently, in the majority of cases, five pins are being utilized: three pins for mains power and two pins for dimming signaling on LED luminaires. With the growing interest in smart cities and IoT sensors, the two extra pins (six and seven) are now being viewed as a straightforward way to connect sensors (e.g., air quality sensors, traffic monitoring sensors). With new capabilities being introduced by smart photocells, an end-to-end solution can be realized.
Since the introduction of the seven-pin NEMA socket, tens of millions of LED luminaires have been installed with it. In most cases, the extra pins (six and seven) are not used. In fact, the wires inside the luminaire are not connected to anything. This large installed base provides an opportunity for cities, utilities, or other owners to install sensors and devices that collect specific data considered valuable to that customer.
Taking advantage of pins six and seven of the NEMA socket is one way to expand a connected city’s applications by designing sensor interfaces to meet customer needs. The ANSI C136 Committee is working on standardizing the interfaces and communications protocols supported on pins six and seven. However, many manufacturers have implemented solutions that are available in the market today.
ZHAGA BOOK 18
More and more smart streetlight projects in Europe specify the Zhaga socket on the luminaire’s top. Zhaga- based controllers source the low-voltage power from LED drivers, which reduces the cost, reduces size, and provides reliability because there are fewer electronic components in the controller. Furthermore, by adding a second Zhaga socket on the luminaire’s bottom, a sensor can be deployed. However, in some cases, these sensors must consume very little power because there are limitations on how much auxiliary power is available from an LED driver used to power the controller. The Zhaga socket is applicable only to DALI wiring schemes.
- Millions of LED luminaires have been deployed with this feature.
- Sensors can be added to any streetlight in the field with limited changes to luminaire wiring.
- Many applications for connected cities (monitoring for traffic, air quality, dynamic lighting) can be deployed, adding flexibility of use, including those with higher power requirements.
1. Can be aesthetically unappealing to some, with the devices on top of a luminaire.
Zhaga Book 18
- In some cases, lower cost of ownership as the controllers are powered by the LED drivers in the luminaires.
- Provides signaling and power for low-powered sensors.
- Some lower-profile controllers may improve aesthetics.
- Added complexity for connected city sensor use cases with higher-power requirements.
- May include higher upfront cost equipment reliant on DALI wiring schemes.
In summary, the outdoor lighting controls industry is going through significant changes as cities and utilities around the world consider their options for adding smart sensors to support the growing interest in connected communities. The choice of physical interface(s) on the lighting fixture itself is an important decision that may determine the ecosystem of sensors that can be considered. ei