Shedding Some Light On 0-10V Dimmable Lighting Fixtures


A vdimmable lightingery popular way to decrease energy usage these days is to use dimmable lighting fixtures and throttle back on the electrical lighting when outdoor light is available through windows or skylights. A light sensor such as the Kele MK7 family can feed light level information into a building automation system (BAS). The BAS can then use an intelligent algorithm to vary the electrical lighting level with changing outdoor light levels to maintain a constant level of indoor illumination while saving energy.

In order for the BAS to command the dimmable lighting fixtures to the desired light level, some sort of control interface must exist between the BAS and the light fixtures. There are several types of light dimming systems out there in the world with different control interfaces.   The one we want to discuss today is known as the “0-10V current sinking” dimming system. We will also briefly mention several other types of light dimming systems, but they are not the focus of today’s article.

Classic Phase-Chopped High Voltage Light Dimmer System

The first light dimming system we’ll briefly touch on is the classic phase-chopping system. These dimmers connect in series with the high-voltage line to the lighting load and perform the dimming by removing part of each half-wave of the AC cycle:

dimmable lighting figure 1

This dimming system is typically limited to small-to-medium incandescent loads although some of the newer CFL and LED light bulbs will work with it also.  These dimmers are typically manual-adjust units without any control interface to a BAS.

Networked Digital Light Dimming Systems

DMX is a networked digital light dimming/control system used in theaters and at rock concerts.  DALI is a networked digital light dimming/control system that is popular in Europe and has found some use in the USA.

“0-10V Current-Sinking” Light Dimming System

This is the dimming system we want to discuss today.  It is formally defined in the standard IEC 60929 Annex E.

Although the interface is named “0-10V” it’s not like the 0-10V analog interfaces we are accustomed to in the HVAC world!  In the HVAC world the 0-10V is generated in the controller and is consumed by the load like this:

dimmable lighting figure 2

The classic 0-10V analog interface shown above is NOT the same as the 0-10V dimmable lighting interface!  The “0-10V Current Sinking” lighting interface is implemented as shown in the following diagram:

dimmable lighting figure 3

Wow, that’s quite a bit different than what we are used to!  The voltage source for the 0-10V signal is actually contained in the lighting fixture, not in the controller!

The voltage source is typically more than 10V, something in the 11-20V range.  A series resistor located inside the lighting fixture allows the light dimmer module to “pull down” the original voltage to the desired value.  The dimmer module does this by varying its own internal resistance until the desired voltage appears across its output terminals.  Those of you who have studied circuit theory will recognize the combination of light fixture resistance and dimmer module resistance as a classic “voltage divider” circuit.

You will notice that a small current flows around the loop from light fixture to dimmer module and back to the fixture.  The value of this small current is NOT the control signal, the voltage across the terminals is the control signal.  The small loop current is just a necessary evil to make the voltage divider circuit work as needed.

Hmmm… I’m getting the idea that a standard 0-10V output from a BAS controller may NOT work with a 0-10V dimmable lighting fixture.  Is that correct?

That is correct.  Your 0-10V BAS output might work with a dimmable lighting fixture if you are very lucky.  But probably, it won’t work.  If you’re unlucky, you might burn up the 0-10V output on your BAS controller.

So… I need a specialized dimmer control to drive these 0-10V lighting fixtures.  Where can I get such a dimmer control? 

We’re glad you asked. J  Kele sells the LDIM2 light dimmer module which is specifically designed to interface with 0-10V current-sinking dimmable lighting fixtures.  The LDIM2 can accept standard 0-10V or 2-10V or pulse-width input signals from your BAS controller and provide the necessary current-sinking 0-10V output for the light fixtures.  The 0-10V current-sinking output to the light fixtures is electrically isolated from the BAS signal inputs to prevent any interference between the two systems.

Can one LDIM2 dimmer module control multiple lighting fixtures?

Yes it can, just wire up the wire pairs from multiple lighting fixtures in parallel like this:

dimmable lighting figure 4

The total current flow through the LDIM2 output will be the sum of all the individual lighting fixture currents.  Different makes and models of fixtures may supply different current values.

How many lighting fixtures can I attach to the LDIM2 output?

That depends on the control current flow from each lighting fixture.  The maximum load current allowed on the LDIM2 output is 0.5 amps.  So you can add lighting fixtures until the total from all the fixtures reaches 0.5 amps, but you can’t go further.  If, for example, each fixture supplied 1 mA of current, you could attach 500 fixtures to one LDIM2 (0.5 amps / 0.001 amps = 500).

If you have so many lighting fixtures that the total control current exceeds 0.5 amps, wire them up in “banks” where each bank is 0.5 amps or less and is controlled by its own LDIM2 dimmer.

How do I find out how much current a particular model lighting fixture puts through the LDIM2?

The IEC 60929 Annex E standard specifies that the control current value should be between 10 uA (microamps) and 2 mA (milliamps).  However, there’s absolutely no guarantee that the lighting fixture manufacturer adhered to these guidelines.

If you’re really lucky, maybe the lighting fixture data sheet will tell you the value of the control current.  If you cannot find a published value for the control current, please don’t just assume a value.  Also don’t mistake the lighting fixture’s supply current for the fixture’s control current.  The fixture’s supply current will almost always be on the data sheet, but will be a much higher value, possibly several amps.

If you have access to the physical light fixture(s), you can measure the control current with your DC mA meter.  Just put it across the two signal wires coming down from the fixture(s).  But beware, the mA meter resistance is less than 1 ohm.  It will pull the voltage down very close to zero volts, and the lights will go dark, so don’t do this during work hours on an occupied space unless the people are warned first!

What happens if the fixture wires are connected to the LDIM2 with the polarity reversed?

If the lighting fixture wire polarity is hooked up backwards, the voltage will go to about 0.7V which is near 0% light level.  Nothing will be damaged, but the lights will go out.

How can I test the LDIM2 on my workbench if I don’t have a dimmable lighting fixture available? 

You can use a standard 24VDC supply and a pull-up resistor like this:

dimmable lighting figure 6

The catalog description of the LDIM2 is “fluorescent dimming control.”  Will it work with dimmable LED lighting fixtures?

Yes, it will work with any dimmable lighting fixture that uses the 0-10V current-sinking interface.  You just need to figure out what control current the fixture puts through the LDIM2’s output so you don’t overload it by attaching too many fixtures.


The 0-10V current-sinking interface used by dimmable lighting fixtures is not compatible with the standard 0-10V outputs used in HVAC/BAS systems.  You should use a specially-designed dimmer control module such as Kele’s LDIM2 for dimmable lighting fixture applications.

47 Ways to Wire Your Power Meter Wrong

Some of you might remember that back in 1975 Paul Simon had a hit song entitled “50 Ways to Leave Your Lover.” Well, coming in a close second are the number of ways (47 of them) that you can wire a 3-phase power meter incorrectly! In this article we’ll briefly discuss why there are so many ways to incorrectly wire a 3-phase power meter and how you can try to insure that your wiring is correct.

Six Different Inputs to Deal With

A 3-phase power meter has 6 different input signals which must be present and connected correctly in order to measure power accurately:

  • There are 3 voltage inputs (we will refer to them as L1, L2, L3) which are connected to the three “hot” wires of the power system being monitored.
  • There are 3 current inputs (we will refer to them as CTA, CTB, CTC) which are connected to 3 “Current Transformer” sensors (CTs).  The CTs have holes through their centers and the L1, L2, L3 hot wires pass through the holes in the CTs.  The CTs measure the currents flowing in the hot wires.

A picture may help to clarify our word description:

Note that a “Neutral” power wire is also shown on the drawing .  This wire will be present on a 3-Phase Wye power system and absent on a 3-Phase Delta power system.  This article is valid for both scenarios.

The L1/L2/L3 wiring is straightforward.  A single wire is run from each “hot” wire to its corresponding L1/L2/L3 input terminal on the power meter.  The CT installation and wiring are a bit more complex, however.

Note that each current transformer has two wires on its output which run to the power meter, and the power meter has 2 screws labeled “X1” and “X2” for each CT input.  Normal convention is that the wires from the CT are colored white and black, and the white wire connects to the X1 screw while the black wire connects to the X2 screw.

The body of the CT has one side designated “H1” and the other side is “H2.”  This could be done with labels or molded directly into the plastic CT body.  The CT should be installed with the H1 side facing the power source and the H2 side facing the load.

How to Get It Wrong – Cross Wiring the CTs and L1/L2/L3 Wires 

In the drawing below, current transformers CTB and CTC have been cross-wired with L2 and L3:

Note that CTB is around the L3 wire and CTC is around the L2 wire.  In this scenario, the power meter will calculate Phase A power correctly, but Phase B power and Phase C power will both the incorrect, resulting in the total power also being incorrect.

Here is a diagram showing the different ways that CTA, CTB, CTC can be paired with L1, L2, L3.  Each diagonal line represents an incorrect cross-wiring between the CTs and hot wires:

How to Get It Wrong – Reversing the CT Polarities

In the drawing below, current transformer CTC has been installed over hot wire L3 with the “H1” side facing the load instead of the power source:

With CTC’s H1 facing the wrong direction, the power meter will either read a Phase C power of zero (if meter is not capable of bi-directional power measurement) or it will read a negative power (if meter is capable of bi-directional power measurement).  Either way, the total power measurement is going to be incorrect.

With three CTs, each capable of being installed with plus or minus orientation, there are 8 possible combinations of CT polarities:

Combining CT Cross-Wiring and CT Polarity Possibilites 

Below is a diagram showing the possible CT cross-wiring combinations and the possible CT polarity assignment combinations.  Note that out of all the possible combinations, there is exactly one combination that measures total power correctly!

Symptoms of Incorrect Meter Wiring 

Incorrect CT-hot wire matching or reversed CT polarities will give lower-than-expected power readings or even negative power readings.  Power factor will also read unusually low on the cross-wired phases.

What’s A Poor Installer To Do?

To have a chance of getting it right, you need to pay scrupulous attention to wire assignments.  Use different wire colors and/or use stick-on wire tags to unambiguously designate the wire functions at both ends of the wire runs.

Determining Correct Wiring Configuration On An Installed Meter

If you suspect that your meter wiring might be wrong, the best way to determine correct wiring is to physically trace everything out.  However, this may be difficult or impossible to do on some installations (for example CTs are sometimes buried inside switchgear which is locked for safety reasons).

If physical wiring inspection isn’t possible then “in theory,” if you are monitoring a constant load, you could rearrange the wiring to try every combination in the table above looking for the highest total KW reading.  This isn’t very practical as it would require a tremendous amount of physical wire swapping and it’s unlikely that the load would remain constant during the length of time it would take to do all the wire rearranging.

Some power meters such as the Kele endicator meter will allow the user to electronically rearrange the wiring without physically moving the wires on the terminal blocks.  Both the endicator LCD/keypad and endicator Desktop Software can be used to change the CT-hot wire matching and CT polarity assignments without picking up a screwdriver.

Even with electronic wire-switching capability in the meter, it would still be quite a challenge to keep track of which combinations had been tried and which combinations were still to be tested, all the while hoping that the load remained constant.

Auto-Configure To The Rescue

The Kele endicator power meter was designed with a special Auto-Configure feature to aid the meter installer in determining proper meter wiring.  Auto-Configure can be invoked from the endicator LCD/keypad or endicator Desktop Software.  When invoked, Auto-Configure analyzes all 6 of the incoming signals in a 3-step, 30 second process.

At the end of 30 seconds, Auto-Configure will return either a Pass or Fail message.  If Auto-Configure passed, endicator will use the new wiring configuration automatically.  You don’t have to do anything further!  If Auto-Configure failed, endicator will continue to use the configuration that was active before Auto-Configure was run.

Does Auto-Configure Work Every Time?

We’d love to say yes, but the honest answer is that it works most of the time.  There are a few reasons that Auto-Configure might not work on your installation:

  • Insufficient or missing CT signals:  all CT signals must be present and the load should be at least 5% of full scale.  If Auto-Configure fails, make sure all the CT wires are connected and there is a sufficient load, then try again.
  • Missing L1/L2/L3 signals:  all L1/L2/L3 hot wire voltage signals must be present.  If Auto-Configure fails, use a voltmeter to verify that L1/L2/L3 voltages are all present.  If any voltage is missing, make the connection and try again.
  • Load changes:  the load should be stable during the 30 seconds that Auto-Configure is running.  If Auto-Configure fails, try several more times.  If loads change dynamically during one part of the day but are more steady at another time, try Auto-Configure at the more stable time.
  • High levels of power system noise:  some equipment like variable-frequency drives (VFDs) can inject high levels of noise into the power system.  If you have VFDs as part of the load, try turning them off and retrying Auto-Configure.


There are many ways to wire a 3-phase power meter wrong and only one way to wire it correctly.  Use color coded wire and/or wire tags to clearly identify each wire at the power system connection points and at the meter connection points.

If the power system connection points will be inaccessible later (locked up inside switchgear for example), try to do you meter testing early when you still have access to the power system connections.

If you have installed a Kele endicator power meter, give Auto-Configure a try and let it check the wiring for you in 30 seconds!

Temperature Sensor Curve ID Numbers


Need help figuring out what type sensor you need for your automation system?  This handy temperature curve chart might help.  If not, give Kele a call!


Sensor Type Temperature Sensor Description  Typical Sensor User
3 10,000Ω @ 77°F, Type III material    AET, American Automatrix, Andover, Carrier, Delta, Invensys, Teletrol, York
21 2252Ω @ 77°F, Type II material Anderson Cornelius, JCI (A319)
22 3000Ω @ 77°F, Type II material Alerton, ASI, ATS, Snyder General
24 10,000Ω @ 77°F, Type II material Alerton, Automated Logic, TAC (INET), Triangle Microsystems, Trane
27 100,000Ω @ 77°F, Type II material Siemens (Landis and Staefa)
42 20,000Ω @ 77°F, Type IV material Honeywell (XL)
63 1000Ω nickel RTD @ 70°F JCI
81 100Ω platinum RTD @ 32°F,
385 curve
Transmitter available for any user
85 1000Ω platinum RTD @ 32°F,
385 curve
JCI, Siemens, Trane (transmitter available for any user)
91 1000Ω platinum RTD @ 32°F,
375 curve
JCI, Trane (transmitter available for any user)
5 1000Ω Balco RTD @ 70°F TAC (Siebe) (transmitter available for any user)


Extend Your Reach with the ST-A Series by Precon

Kele’s Precon brand has a sensor solution for ALL your application needs, even the odd ones!

Job site situation #1: You need a temperature sensor for your tank or cooling tower sump, but they don’t make one long enough. Special ordering one seems daunting. What if it doesn’t work out and you can’t send it back? Precon has a solution for you. If your sensor probe isn’t long enough to reach your desired depth, create an extension! This solution allows you to measure the temperature without having to drain the tank or drill a hole. It also prevents you from having to buy a special length sensor and well. By simply creating a PVC pipe extender as shown below, and attaching Precon’s ST-A* temperature sensor to the other end, you’ve solved your unique application with a very simple, and in-stock (*) Precon sensor.

Drawing 1

Job site situation #2: You need several sensors within the same well or tank, detecting the temperature throughout your pool. You can use a similar solution to the one shown above with just some additional PVC pipe as shown below. Run your wires through the pipe and affix the conduit to the side of your tank or well and voila! Precon solves another problem!

Drawing 2

* ST-A sensors not typically requested may not be stocked.

Power Monitoring – Harness the Power!


Update!! The ENG-ETH Ethernet Communication Module for endicator is now available. It reads data from the endicator™ main processor, formats the data, and transmits it over Ethernet using BACnet IP, Ethernet IP, and Modbus TCP protocols. The module also hosts a website where meter status can be viewed using any browser that supports Adobe Flash.



For 30 years Kele has been the building automation industry distribution leader, providing parts, solutions, and world class personal customer service. Kele works hard to stay ahead of the curve when it comes to industry changes while always focusing on maintaining the highest level of customer service.  Our power monitoring offering is no exception. Kele has been offering a wide variety of power monitoring brands and products since 1983 and building power monitors since 1993.

Power monitoring is not new to the building automation and energy management industries. Those that have been around building automation and energy management systems can, almost jokingly, say “We were green before green was a thing.” However power monitoring has changed. With the growing focus on saving energy and resource management, power monitoring has been thrust to the forefront of building automation and energy management.  Enter endicator™. Kele’s new power monitor.


Kele’s endicator™ power monitor, introduced earlier this year, is the cutting edge of power monitoring devices. Designed with future upgradability in mind, the endicator™ power monitor gives user the ability to make changes and perform upgrades in the field. Firmware, communication capabilities, and other features can be upgraded according to changes in your customer’s needs. This kind of forward thinking sets endicator™ apart from the others. Think of it as “future proof”.

Here are just a few of the many features of the endicator™ power monitor:

  • NEMA 4 enclosure standard
  • KWH Accuracy class 0.5% ANSI C12.20 For meter alone with unmatched CTs.
  • 0.5% system accuracy with factory calibrated matched CTs.
  • Data port for setup and trend retrieval
  • Measure voltages up to 32,000 VAC (voltages over 600 VAC require the use of a potential transformer, not included)
  • Supports 0.333V safe CTs and 5A CTs (must use optional 5A adapter board)
  • BACnet MSTP, LonWorks, N2 and Modbus RTU available
  • Password protected configuration
  • Powered by separate 24 VAC supply
  • On-board data logging
  • Auto configuration
  • Upgradable firmware through data port
  • Bidirectional power measurement
  • CSI (California Solar Initiative) approved

Kele doesn’t stop there. We also offer power monitoring units from Honeywell, Veris, and WattNode.

Honeywell H-Series The Honeywell H-Series 500 submeters, available from Kele, feature a direct-read 8-diget LCD display of cumulative kWh. The H-Series 500 also is UL Listed and meets or exceeds ANSI C12 national accuracy standards. Communication options include Modbus RTU or TCP/IP, BACnet IP or MSTP, and LonWorks.
Veris’ E50 Series power meters, also available from Kele, provide a solution for measuring energy data with a single device. The E50 series is conveniently mounted on DIN rail, has password protection capability, and works with popular 0 to .333V or 0 to 1V current transformers. Veris E50
 WattNode The WattNode NC series AC power meters can communicate over 50 values via BACnet and over 27 values via LonWorks. WNC series meters have diagnostic LEDs that provide per-phase indication of power to help with installation and troubleshooting.

These are just a few of the many power monitoring devices that are available from Kele. We also have current transformers, current transducers, voltage potential transformers, and more – all with Kele Inventory, Kele Service, and Kele Technical Support. Check out our complete power monitoring line at Kele – Your Source For power monitoring.

AC to DC – Linear Versus Switch-Mode Power Supplies

For years, Kele has provided dependable, quality 24 VDC power supplies like the DCP-1.5-W, DCPA-1.2, DCP-250, PW2, and the SLS Series. All of these DC power supplies are “linear” power supplies. Another type of DC power supply gaining popularity with building automation and temperature control contractors is called a “switch-mode” power supply (PS6R Series). While both linear and switch-mode power supplies ultimately perform the same task, it is the design technique used to convert AC voltage to DC and the resulting advantages that differentiate the two types.

How they work

To convert AC voltage to 24 VDC, a linear power supply first uses a relatively big, heavy transformer to step down the AC line voltage to a lower voltage around 30 VAC. The transformer also provides electrical isolation by separating the AC line neutral or ground from the power supply’s output. The reduced AC voltage is rectified into a pulsating DC voltage using one (half-wave) or two/four (full-wave) diodes. The pulsating DC voltage is then filtered or smoothed using a large value electrolytic capacitor. Finally, the filtered DC voltage is controlled by a linear regulator to output a constant voltage, even with variations of the input line voltage, the output load, and temperature. The regulator also helps to suppress any output ripple voltage.

Switch-mode power supplies use a different method to convert AC to DC. First, the 60 Hz AC line voltage is rectified and filtered using diodes and capacitors resulting in DC high voltage. Power transistors, typically switching at a preset frequency anywhere from 20 kHz to 500 kHz, convert the high voltage to a higher frequency AC. The high frequency AC is then reduced to a lower voltage using a relatively small, lightweight transformer. Finally, the voltage is converted into the desired DC output voltage by another set of diodes, inductors, and capacitors. Corrections to the output voltage due to load or input changes are achieved by adjusting the pulse width of the high frequency waveform.

Advantages and drawbacks

Size and weight

Linear power supplies operating at 60 Hz require relatively large and heavy transformers. Because switch-mode supplies operate at high frequencies, much smaller transformers are used, making switchers substantially lighter and more compact. For example, a 7.2A output linear supply weighs 14 pounds, mostly due to the large transformer required. However, a 10A output switch-mode supply weighs only 4.4 pounds. The small size and light weight of switch-mode supplies make them well suited for DIN rail mounting in control panels.

Linear supplies that are available with a single voltage input transformer must be ordered for a particular application. Some linears have multi-tap input transformers allowing some application flexibility but they still must be manually tapped for the correct input voltage in the field. Most switch-mode supplies will operate with any voltage from 85 to 264 VAC connected directly to their input, without manual configuration.


After filtering and regulating, some small amount of undesirable AC voltage will still remain superimposed on the DC output of a power supply. Linear power supplies are quite effective at minimizing noise. A typical specification for noise on the output of a linear power supply is 3 mV peak-to-peak or 0.0125% of a 24 VDC output. Switch-mode power supplies are noisier with a typical maximum specification of 2% of the output voltage or 480 mV on a 24 VDC supply. While some applications like audio equipment or very delicate test equipment may be sensitive to noise on the output of a switch-mode supply, most BAS/HVAC control applications will not be adversely affected.


The efficiency of a power supply is the ratio of its total output power to its total input power. Linear power supplies operate with only 40% to 60% efficiency due to energy lost in the form of heat dissipated through large heat sinks. Switch-mode power supplies are much more efficient, operating around 80% to 90%.


Linear power supplies have been proven to be reliable but operate somewhat inefficiently. They are relatively noise-free but are generally heavy and bulky because they require large transformers.

In contrast, switch-mode power supplies are small, lightweight, and highly efficient. Although they produce more noise on their output than linear supplies, that is not a factor for most BAS applications.

Whether you need linear or switch-mode, count on Kele to make it easy for you to find the best power supply for your application.