Interfaces between external control devices and lighting assets: NEMA or Zhaga-D4i?

Smart City
Connectivity

For cities considering a lighting upgrade, Schréder can offer everything from repairing existing assets, to fitting entirely new street lights and connecting them to a Central Management Systems (CMS), such as Schréder EXEDRA.

One simple decision when planning a lighting upgrade can make the difference: choosing a connected-ready solution. For more information on this, read our white paper which explains what connected-ready luminaires are, why they are useful and what options planners have when selecting them.

One of the biggest decisions facing system owners is whether to choose a NEMA or Zhaga ecosystem. This technology page explains both interfaces in greater detail, explaining the standards they relate to, and the resulting impacts of their different architectures so that system owners can make an educated choice. 

Both NEMA and Zhaga are futureproof, interoperable and robust. While we believe that Schréder EXEDRA is the most functionally and scalable complete CMS on the market, we also believe that customers can choose whichever ecosystem best suits their city. 

Origins and Regional Differences

NEMA

NEMA stands for the National Electrical Manufacturers Association, which was founded in the USA in 1926 and writes standards for electronic products.
ANSI C136.41 is the standard specifying the interface between external control devices and lighting assets, and is mainly used in the US, UK, Australia and New Zealand, where it is commonly referred to as the NEMA interface. It has also been adopted by other countries.
 

ZHAGA 

The Zhaga Consortium was established in 2010 to set standards for the interfaces of components used in LED luminaires. The consortium is a member program of the IEEE Industry Standards and Technology Organisation.
Zhaga’s specifications, called Books, address electrical, mechanical, optical, thermal and communication interfaces and enable component interoperability. Zhaga’s specifications are enforced by a certification programme so that compliance with the books is assured by independent test bodies. The book that specifies the outdoor luminaire extension interface is Book 18. The first edition was published in 2019. It is now widely accepted as a de facto standard in most countries.

Different electrical architectures

NEMA

In a NEMA architecture, the AC mains supply is first connected to the receptacle so that the power supply passes through the node before it reaches the luminaire and its driver. A NEMA controller is connected directly to the mains supply, and is powered before the luminaire.
As a result, in addition to providing connectivity and a dimming interface for the luminaire control system, the controller also includes surge protection, AC/DC low-voltage power supply conversion, energy metering, and load switching. 

ZHAGA

In a Zhaga architecture, the AC mains supply reaches the luminaire first, and the Zhaga receptacle is only connected to low-voltage auxiliary power supplied by the driver. Therefore, with such an architecture, the driver in a Zhaga-D4i luminaire has more capabilities than a conventional driver, such as enhanced surge protection, auxiliary power supply, energy metering and diagnostics. On the other hand, a Zhaga-D4i certified controller is significantly simplified as it is not connected to the mains.

Connection options

NEMA

The ANSI standards specify multiple NEMA receptacles in terms of pin count (3-pin, 5-pin or 7-pin connectors) and pin assignments. As a result, the NEMA interface can be used with several alternative protocols. It is therefore more flexible to accommodate different applications. However, ensuring full interoperability between the luminaire and its peripherals is more difficult given the multiple alternatives supported by the ANSI standards.

ZHAGA

Zhaga Book 18 aims for full interoperability so that certified components are interoperable, easy to service and replace, and that a Zhaga-D4i LED luminaire can be safely upgraded after installation. To ensure this promise of interoperability, the Zhaga Book 18 specifications allow only a unique pin count and assignment that must be accommodated by any application.

Power capabilities and electrical safety

NEMA

Any device connected to the luminaire through a NEMA receptacle is connected directly to the AC mains supply. The power available for such devices is thus only limited by the current carrying capacity of the NEMA receptacle itself. In this respect, the NEMA architecture is very useful for nodes that have to deliver power-demanding functions.
As the AC power is shared between the luminaire and its peripherals via the NEMA interface, the design and operation of the NEMA ecosystem must comply with appropriate electrical safety regulations.

ZHAGA

Any device connected to a Zhaga-D4i luminaire via a Zhaga receptacle is powered by the auxiliary power supply available in the luminaire. The maximum number of peripherals and their power consumption are then limited to ensure the interoperability of the system. The nodes must respect these limits, regardless of the functions that they provide.
The auxiliary power supply available on the Zhaga receptacle is low voltage, which helps to simplify the electrical safety context when designing and operating this ecosystem.

Electrical metering capabilities

NEMA

In the NEMA architecture, the luminaire controller is connected directly to the mains supply and is powered ahead of the luminaire. The node will then typically incorporate an electrical metering capability to measure and monitor the power and energy consumption of its load. The metering accuracy and periodicity will depend solely on the specifications of the luminaire controller.

 

ZHAGA

A Zhaga-D4i luminaire controller designed to operate on a low-voltage Zhaga socket is not connected to the mains supply. It is therefore unable to directly measure any electrical parameter related to the performance/energy consumption of the luminaire. With a Zhaga-D4i luminaire, the metering capability is built into the luminaire's power supply, typically a D4i driver, while the node simply reads this data from the power supply via the digital interface.  The metering accuracy and periodicity will depend on the specifications of the power supply in the Zhaga-D4i luminaire and is not part of the Zhaga Book 18 specifications.

Data capabilities

NEMA

The ANSI standard supports several control signals, some of which are analogue, such as 1-10V, and some of which are digital, such as DALI. Therefore, the ANSI standard does not specify any set of data being exchangeable between the luminaire and its peripherals, as the communication protocol used between them may vary from one application to another.

ZHAGA

Zhaga Book 18 uses the so-called D4i digital bus and protocol specified by the DALI Alliance. The Zhaga D4i certified luminaires and modules therefore interact digitally to exchange a number of data sets such as luminaire information and electrical metering/monitoring in a standardised format.

Product lifespan

  

NEMA

In the NEMA architecture, the luminaire controllers are directly exposed to the AC mains supply and may be subject to electrical transients and surges that can affect their lifetime. They remain permanently connected to the mains while electrically disconnecting the luminaire from the mains during the day, thus preserving the luminaire lifespan on a 24/7 mains grid.   

ZHAGA

As described in Zhaga Book 18, the luminaire controller on a Zhaga socket is never exposed to the mains supply, reducing the potential impact of electrical transients on its lifespan. The luminaire’s internal power supply remains permanently connected to the mains supply, so that both the luminaire and the node remain switched on and operate in standby mode during the day on a 24/7 mains grid.

Aesthetics
NEMA

As they contain a significant number of components and functions, NEMA controllers are relatively large compared to the size of a street light, which can affect the overall aesthetics of the ensemble.
 		 ZHAGA

Zhaga-D4i controllers are typically half to one-third the size of a typical NEMA controller, making them less visible on the luminaire.

Cost

NEMA

NEMA controllers have more components and therefore tend to be more expensive. If you install a connected-ready luminaire with a NEMA socket, but no node, you must use an electro-mechanical shorting cap. Otherwise, the NEMA luminaire will not work. Such shorting caps add additional costs to the system.

ZHAGA

Zhaga-D4i controllers do not need AC/DC conversion or a metering circuit, so they tend to be a lower-cost component, while a Zhaga-D4i luminaire may be more expensive as it needs a driver with enhanced capabilities.
If you install a connected-ready luminaire with a Zhaga socket, but no node, a simple mechanical cap is sufficient to protect the socket. This cap can be removed when a Zhaga-D4i controller is mounted on the street light.


Every city is different. The best way to choose between NEMA and Zhaga-D4i interfaces is to determine the objectives for the lighting infrastructure and how the light will be used in different areas. Both options bring potential shortcomings and benefits for future smart lighting control, and each ecosystem is open to deliver flexibility and modularity. This is why Schréder supports both the Zhaga-D4i and NEMA options. As ever, the customer is at the heart of the process.