The Traffic Signal Museum

NEMA Traffic Signal Controller

This is the second real traffic controller in my collection. It is a NEMA (National Electrical Manufacturers Association) controller. The National Electrical Manufacturers Association developed the standard for this controller so that all NEMA controller parts can be interchanged between cabinets without compatibility issues.

There are two main types of NEMA controllers. The first is TS1, which is shown here. Eventually, equipment became more advanced and NEMA TS2 was developed. There are also two types of TS2, type 1 and type 2. See the bottom of the page for a brief explanation of TS1, TS2 and TS2 type 1 and 2.

NEMA controller

This is just a basic set up. I do not have a NEMA cabinet, so I had to build a wood case to keep the controller locked up when it is running because of the obvious electrical danger. This is a four phase controller set up. It allows for main street and side street thru signals as well as left turn signals for both AND overlaps for both which would be a green and yellow turn arrow while the thru signal is green. It also has pedestrian signal capabilities for main street and side street. The controller panel also came with a police and tech panel. The police panel has only a few functions on it that are also available on the tech panel, so if I ever hook up any of these, I will only use the tech panel and not the police panel. The tech panel has switches on it for pedestrian signal push buttons and vehicle sensors which can be turned on or off. Right now I have the controller set to "think" it is constantly receiving pedestrian and vehicle "calls" so that it continuously sequences back and forth. In the future, I could hook up push buttons or motion detectors to simulate pedestrian and vehicle sensors.

NEMA controller

This is the actual controller box itself. It is a Traconex 390. The programming menus for this controller are a bit intimidating at first, but eventually you can understand the basic layout of the menus. There are a lot of features on this controller that I will never need to use in my little basement display. There are also features I do not even understand. These controllers are capable of a lot of different things and are far more advanced than my other real controllers, the Eagle EF-15 and EF-70, the Marbelite M20 and the Crouse Hinds KS electro-mechanical controllers.

NEMA controller

Here is a close up of the display on the controller. It is saying that phase 2 has a pedestrian call with the P indication. The 4 indicates that phase 4 timing is being displayed. Currently the phase 4 walk timing is being displayed by the WLK for WALK and 006 seconds left before DONT WALK flashing clearance begins. The RDD indication on the bottom is where phase 5-8 information would be displayed if this was an 8 phase controller, but since it is only a 4 phase, RDD is always displayed on the bottom. RDD stands for Red Dwell.

conflict monitor

This is the conflict monitor. Its function is to monitor for problems, like a green light for conflicting phases, that could confuse drivers or cause an accident. If a problem is detected it puts the controller into flash and stops the controller box right at the point that the problem was detected.

Load Switch frontLoad Switch back


This is a load switch. The controller operates the load switch with 24 volt DC. The load switch is like a solid state relay in that it turns on and off the 110 volt AC signal indications based on what the controller tells it to do. There are LED indications on the front of the load switch to show what signal lamp it has turned on at any given time. It also works with pedestrian signals, but the middle LED (yellow indication for vehicle signals) is not used with pedestrian signals.


In the fall of 2012, I was able to purchase a used NEMA cabinet with a panel already installed and fully functional. All I needed to do was to unhook all the signals from my plywood box setup shown above, take the load switches, flasher and flash transfer relays out of the old panel, install them in the new cabinet and wire up the signals. Here are a couple of pictures of the new cabinet. I am still using the same controller, a Tranconex 390 in the new cabinet.

As I said above, the setups on this page are TS1. 

TS1 is the original specification. It requires a conflict monitor and the A B and C large cables that run down to the back panel. It standardizes the load switches, electronic specs and detectors. Everything is hard wired--there's a wire for all inputs and outputs.

TS2 is the new specification and is broken down into TS2 Type 1 and TS2 Type 2

TS2 Type 1 is strict TS2 operation. The A/B/C cables are replaced with a SDLC (Synchronous Data Link Communication) line. An "A" plug is only used for power. The SDLC line ties between most/all the electronics in the cabinet. Much wider flexibility for customization, less wiring, and the equipment talks back and forth with each other. The conflict monitor is replaced with a Malfunction Management Unit. TS2 Type 1 NEMA cabinets use Bus Interface Units (BIUs) to interface and talk to the load switches and other equipment.

TS2 Type 2 is like a hybrid of TS1 and TS2. It uses an SDLC line to talk to the malfunction unit and/or the detectors only, but the back panel and load switches still use the TS1 A/B/C cables to retain the point-to-point wiring for the load switches, etc.

Thanks to Nick B. for the information on the different NEMA specs.


This page was originally posted on 7/16/2002.

This page was last updated on .

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