Kele Blog

Shedding Some Light On 0-10V Dimmable Lighting Fixtures

Posted on by Kele Inc

 

A very 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:

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:

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:

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:

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:

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.

Conclusions

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.

Networking 101: BAS Network Cabling

Posted on by Kele Inc

The various devices comprising a building automation network are either connected by cables or talk wirelessly to each other, or possibly a combination of both.  In Networking 101, we are going to concentrate on network devices connected by cables.  Let’s take a look at the different types of network cables typically encountered in building automation networks.

Network Cables 

The most common type of network cable used in building automation networks is the “twisted pair” cable.  Two wires are twisted around and around each other at a uniform number of twists per inch to form the “twisted pair”: twisted pair Why twisted pair cable?  Without going into a lot of technical detail, let’s just say that with the proper type of transmitters and receivers using twisted pair cable greatly reduces noise pickup from noise sources such as motors, fluorescent lights, and radio stations.  This results in more reliable communications with less corrupted data and retransmissions.

Not all twisted pair cables are created equal.  There are electrical characteristics such as resistance and capacitance per foot that vary between different brands and models of twisted pair cable.  Generally the lower the resistance and capacitance of twisted pair cable, the better it performs in networks.

It’s a good idea to select a network cable that’s specifically recommended by the manufacturer for use in your type of network.  If network-specific cable is not available, substitutions can be made.  If the resistance and capacitance per foot of the proposed substitute cable is as low as or lower than the recommended cable, the substitute cable should be acceptable.

Some styles of network cable are available with or without a metallic shield around the outside of the wires.  Shielded cable generally helps with reducing noise pickup, but the cable will cost more.

Now let’s get more specific about the types of physical layers typically found in building automation networks…

RS-485

RS-485 is used extensively in building automation networks.  Modbus RTU, JCI Metasys N2, and BACnet MSTP protocols all use RS-485.

RS-485 uses a single twisted-pair to send the data.  It also uses a third “reference wire” in addition to the twisted pair.  There is debate among users as to whether the reference wire is always needed, and some devices do not include a terminal for connecting a reference wire.  But to be safe it’s always best to include it in the cable: Twisted Pair with Reference Wire RS-485 devices typically use screw terminals for connecting to the cable.

The two wires of the twisted-pair do have a polarity assigned to them.  The same wire of the pair must be connected to the RS-485 “+” terminal of all the devices on the network.  If an RS-485 device is connected to the network with the “+” and “-“ wires attached backwards, it will not talk on the network!

RS-485 cable should be run as one continuous “trunk line.”  The RS-485 standard specifies that as many as 32 devices can share the same trunk line, and the line can be as long as 4000 feet.

It is bad practice to “tee” into the middle of an RS-485 cable and run a “stub” line off to another RS-485 device:

3

Instead, the RS-485 line should be daisy-chained to each device on the line like this: 4

If an RS-485 cable needs to be longer than 4000 feet a “repeater” module can be inserted in the middle of the cable run.  The repeater will refresh the electrical signals and allow for longer runs.

You can also expand an RS-485 network to more than 32 devices by creating multiple sub-networks, each with its own cable, and connecting the sub-networks together with a “bridge” or “router” device.  A bridge or router will have two or more separate RS-485 electrical ports.  Each port on the bridge/router connects into one of the sub-networks and data can then flow between the sub-networks:

5 A “Bridge” forwards all the traffic on either sub-network across to the other sub-network.

A “Router” has the capability to learn (or to be told through a user-generated lookup table) which devices reside on each sub-network.  Now if two devices on the same sub-network are talking, the conversation is not passed to the other sub-network.  This eases overall network traffic congestion.

FT-10 “Free Topology” (Lonworks)  

The FT-10 “Free Topology” physical layer was invented by Echelon Corporation as part of their Lonworks networking technology.

Similar to RS-485, FT-10 uses a single twisted pair to carry the data, but FT-10 does not use a third  “reference wire”:

6 The FT-10 twisted pair has no polarity – the wires can be attached to each Lonworks device without worrying about which wire is “+” and which is “-“.

Like RS-485 devices, Lonworks FT-10 devices also typically use screw terminals to connect to the network cable.

FT-10 is much more relaxed as to how the cables can be arranged – you can pretty much wire different FT-10 network segments together any way you want to.  You can “tee” into an FT-10 line with a “stub” headed in another direction, or you can make a “star” with a center point and multiple lines radiating out from it:

7 Lonworks FT-10 documentation recommends that the total cable run be no longer than 1640 feet and you put no more than 64 devices on a network.

As was the case with RS-485, you can extend the FT-10 cable distance with an FT-10 repeater.  You can also extend beyond 64 devices by creating sub-networks and connecting them together with an FT-10 bridge or router.

Please note that even though RS-485 and FT-10 both use a single twisted pair to carry the data signals, they are totally incompatible electrically!  You cannot ever tie an RS-485 network cable directly to an FT-10 network cable.  

If you want to communicate between an RS-485 network and an FT-10 network, you must use a “Gateway” device which has an RS-485 port on one side and an FT-10 port on the other side:

8 Ethernet  

Ethernet was invented back in the 1970s by Xerox and is extremely popular in the Information Technology world.  BACnet IP and Modbus TCP protocols use the Ethernet physical layer.

There are several different versions of “Ethernet” networks, but the two we deal with in building automation are the 10BASE-T and 100BASE-T versions.  The only significant difference is the speeds.  10BASE-T runs at 10M (10 million bits per second).  100BASE-T runs at 100M (100 million bits per second).

10BASE-T and 100BASE-T devices can be mixed on a network.  If a 100BASE-T device needs to talk to a 10BASE-T device, it simply drops its speed to the 10BASE-T rate temporarily.

The two styles of Ethernet cables you’re likely to encounter in building automation are designated as CAT5 (Category 5) and CAT5e (Category 5 Enhanced).  Both cable styles can be used with either 10BASE-T or 100BASE-T, but CAT5e cable gives superior performance.

The 10/100BASE-T cable contains four twisted pairs, but only two of them are used to carry the data: 9 The other two twisted pairs may be left unused or used for some other purpose.

Standard length off-the-shelf 10/100BASE-T cables typically come with RJ-45 plugs pre-installed on the ends of the cable.  RJ-45 plugs look like modular telephone plugs except they are wider and have positions for 8 connections.  If you need to make a custom length 10/100BASE-T cable, you can buy a bag of loose RJ-45 plugs and a special wire stripper/crimper tool and attach RJ-45 plugs yourself (but it is a bit tedious to do).

Unlike RS-485 and FT-10, you can only connect two devices with a 10/100BASE-T cable!  And the recommended maximum cable length is only 330 feet.  So how are we able to network many devices together?  The answer is in the use of Ethernet cable-sharing devices such as “hubs” and “switches.”

These hubs and switches have multiple RJ-45 data jacks for plugging in Ethernet cables.  They are used to build out an Ethernet network “like a tree”:

10 An Ethernet ‘Hub” forwards everything it receives on any port out all the other ports on the hub.  So if an Ethernet network is built using all hubs, every end device on the network must listen to every conversation on the network whether it’s involved or not.  This creates a lot of unnecessary traffic and slows down the operation of the network.

An Ethernet “Switch” learns where the different end-devices are located in the network and restricts the traffic flow to only those network segments that are needed to reach the specified end device.  This greatly reduces unnecessary traffic on the network and speeds up response time.

An Ethernet “Router” is used to connect multiple Local Area Networks (LANs) together to form a Wide Area Network (WAN).  There are also Ethernet “Gateways” to connect Ethernet networks to RS-485 or FT-10 networks.

RS-232  

RS-232 is a physical communications layer that is used for making point-to-point connections between 2 pieces of equipment.

You may find that some network devices include an RS-232 port for connecting to a computer to perform device configuration.  This RS-232 port is not for the network connection, only for configuring the device prior to using it on a network.

RS-232 ports on older equipment used 25-pin connectors like this: 11 Modern equipment providing RS-232 ports use 9-pin connectors like this: 12 The connectors come in both male and female versions, so when connecting two pieces of equipment you must the sure that the cable has the correct gender connectors.

A “normal” RS-232 cable will have a male connector on one end and a female connector on the other end with “straight-through” wiring (pin 1 connects to pin 1, pin 2 connects to pin 2, etc.).  But sometimes a custom cable must be purchased or fabricated with male-male or female-female connectors and possibly with crossed wiring between the pins.  The details of these special RS-232 cables are beyond Networking 101.

Connecting A Voltage-Output Signal Source To Multiple Loads

Posted on by Kele Inc

The Tech Support crew here at Kele frequently gets quizzed by customers who have a voltage-output signal source which must drive multiple voltage-input loads. Requests for “voltage signal replicators” come in frequently. Sometimes extra hardware is needed, but sometimes it isn’t! So we thought it might be a good idea to write an article addressing this topic. Here we go…

*** A note about the terms “resistance” and “impedance”

When looking at data sheets for HVAC control modules, you may see the terms “resistance” or “impedance” used in describing signal input/output loading characteristics.  Strictly speaking, “resistance” and “impedance” are different entities (impedance = resistance + reactance) but for a slow-moving control signal which is what we usually have in the HVAC world, the two terms can be used interchangeably.  So don’t worry about whether the data sheet says “resistance” or “impedance” we’ll take them to be the same thing.  In this article we’ll use the term “impedance” because it’s one letter shorter than “resistance” and we’ll save keystrokes!

Impedance is measured in units called “ohms.”  If you don’t know what ohms are, don’t worry.  All you have to do is poke the numbers into some simple calculations later on.  You may see a suffix “k” or “K” appended after the ohms value on a data sheet.  This is important to note!  The “k” or “K” means “times 1000” so an impedance of “100K” means 100,000 ohms and that’s the number you would put into your calculations.

On with the show…

The first thing we must do is answer a few questions about the signal source and loads:

  1. Do the Signal Commons on the different loads have to be isolated from each other?
  2. Does the Signal Common on the voltage source have to be isolated from all loads?
  3. What is the “minimum load impedance” the signal source can drive (data sheet item)? (Alternately, this could be specified as “maximum output current”).
  4. What is the “input impedance” of each of the voltage-input loads (data sheet item)?

The first two questions are sometimes difficult to answer, and are application-dependent.  If you cannot find concrete answers, you can always assume that every device must have isolated signals.  This approach will always work, but it will also cost more money as signal isolator hardware is required.

With regards to question #3, the signal source data sheet may specify a “maximum output current” value instead of “minimum load impedance.”  The “maximum output current” will be expressed in units of mA (milliamps).  No worries, we can calculate what we need by this equation:

Minimum load impedance = Largest output voltage required/maximum output current

As an example, suppose the signal range of interest is 0-10V and the maximum output current available from the signal source is 2 mA (0.002 amps):

Minimum load impedance = 10V / 0.002 amps = 5000 ohms

Calculating “equivalent load impedance”

When connecting voltage loads in parallel, you’ll need to calculate the “equivalent load impedance” of all the loads connected together.  There are a couple of ways to do this:

If all load impedances are the same—

Equivalent load impedance = impedance of one load / number of loads

If the load impedances are different –

Equivalent load impedance = 1 / (1/Load1 impedance + 1/Load2 impedance + …)

The second calculation is most easily done using the 1/X key on your calculator.  Just do a 1/X calculation for each load impedance and add the terms together.  Then do a final 1/X calculation on the first result.  Here’s an example—

Load 1 = 10,000 ohms (10K)

Load 2 = 50,000 ohms (50K)

Load 3 = 100,000 ohms (100K)

Equivalent load impedance = 1 / (1/10000 + 1/50000 + 1/100000)  =  7,692 ohms

The two rules that must be satisfied

There are basically two rules that must be satisfied when driving multiple loads from a voltage source:

  1. If electrical isolation is required, you must add a hardware signal isolator module to each device to be isolated.
  2. At each voltage output-to-input interface, the equivalent load impedance of the loads connected together must be higher than the minimum load impedance of the signal source

Case 1:  It’s OK for all devices to have their Signal Commons tied together 

This case can be done using direct wiring (NO extra hardware) if the equivalent load impedance (calculated above) is greater than the signal source’s minimum load impedance:

 

That’s great UNLESS… your equivalent load impedance is smaller than the voltage source’s minimum load impedance.  Then what are you going to do?

When the equivalent load impedance is too small for the signal source to drive directly, you will need to insert a “signal booster” device of some sort between the original signal source and the loads.  The signal booster doesn’t need to boost the voltage (you typically want the same voltage out that’s coming in).  It needs to boost the available current so there is enough to drive all the loads connected together.

The Kele UAT is a good device to use as a signal booster in this application.  A look at the data sheet shows that its voltage output can drive up to 20 mA of current.  Let’s assume that the signal range of interest is 0-10V so the maximum voltage we ever need to output is 10V.  Then the minimum load resistance supported by the UAT would be:

UAT minimum load resistance = 10V / 0.020 amps = 500 ohms.

This is plenty of drive power for most parallel-connected voltage loads.

Now when we insert a signal booster device, we must insure that the input impedance of the booster itself is not too low for the original signal source.  We see that the UAT input impedance on the 0-10.9V range is 156K ohms (156,000 ohms).  If your UAT data sheet shows 156 ohms input impedance, don’t panic!  It’s really 156K, some data sheets have a typo.  Our apologies.  So the UAT input impedance of 156K is far higher than the signal source’s minimum load impedance of 5K, and it’s all good:

 

Now you should understand that the UAT does not provide signal isolation as it has one Common terminal for both signal input and output.  If you require isolation between devices, read on…

Case 2: Load Signal Commons can be tied together, but voltage source needs isolation

In this case you will need a signal isolator device such as the Kele DT-13E.  On the DT-13E, the input signal terminals are completely isolated from the signal output terminals and both of those terminal sets are completely isolated from the power terminals.

We look at the DT-13E data sheet and see that the input impedance on the 10V input range is 13.3K.  This is higher than the signal source’s minimum load impedance of 5K, so there is no problem driving the DT-13E input from the original signal source.

Looking at the DT-13E voltage output, we see that the maximum current available is 6 mA.  For a 0-10V signal, the max voltage we need to drive out is 10V so the DT-13E’s minimum load impedance will be:

DT-13E minimum load impedance = 10V / 0.006 amps = 1667 ohms.

If we have the same three 10K loads paralleled as in the previous example (3333 ohms equivalent load) then the DT-13E has enough drive and this setup should work just fine:

 

Case 3: Load Signal Commons must be isolated from each other

In this situation, each load will need its own signal isolator module like the DT-13E.  The most obvious setup to use is shown in the next figure.  When we do the load calculations, however, we find that three DT-13E inputs in parallel will present an equivalent load impedance of 13.3K / 3 = 4433 ohms.  Oops, that is lower than the minimum load impedance of 5000 ohms specified for the signal source:

 

How do we fix this problem?  Here are some possibilities:

  1. Use a different signal source with more drive capability.
  2. Use different signal isolators with higher input impedance.
  3. Try rearranging the wiring using the devices that we have.

Let’s see what we can do with option #3.  Realizing that inputs and outputs are isolated on the DT-13E modules, it’s perfectly legal to take one of the DT-13E inputs and drive it from another DT-13E’s output.  Let’s check the math to see if this would work.

With only two DT-13E inputs paralleled on the signal source, the equivalent output impedance would be 13.3K / 2 = 6650 ohms.  This is higher than the signal source’s minimum load requirement of 5000 ohms, so that works.

With the new arrangement, one DT-13E output will drive a parallel combination of the original 10K load and one DT-13E input (13.3K).  The equivalent load impedance will be:

Equivalent load impedance = 1 / (1/10000 + 1/13300) = 5708 ohms.

This is higher than the DT-13E output’s minimum load impedance of 1667 ohms so that works too!  And this is the final configuration:

 

Conclusions

By following the two interface rules discussed above, multiple voltage-input loads may be successfully driven by a common voltage-output signal source.  The math is simple algebra and can be done on any calculator.  Happy interfacing!

47 Ways to Wire Your Power Meter Wrong

Posted on by Kele Inc

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) 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.

Cautionary Note

This article deals with the connections between power systems and the meters that monitor them.  Hazardous, potentially lethal voltages are involved.  See the Stayin Alive footnote at the end of this article for information on keeping yourself safe.

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 Possibilities

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 have the ability to sense a reverse-mounted CT (power is reading negative) and electronically flip the CT signal polarity so the black and white CT wires don’t have to be physically swapped on the meter terminals.  This is a desirable feature and will increase your chances of a successful power meter installation.

Conclusions

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.  Using a power meter with CT polarity auto-correction can eliminate one source of wiring errors.

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

Personal Safety Footnote

Stayin’ Alive, Stayin’ Alive (1977 hit by the Bee Gees)

The connections between a power system and the meter(s) monitoring it involve hazardous voltages.  Described below are two ways you could get zapped working with power meter wiring.  Please don’t!

News Flash:  Power System Voltages are Dangerous

The L1/L2/L3 input terminals on a power meter will have voltages from 120V to 600V attached to them.  Never put your fingers inside a power meter unless these high voltages have been de-energized external to the power meter.  This seems like common sense, but we had to say it.  There, you’ve been warned.

A Tale of Two CTs (or rather two CT Styles)

Current Transformers (CTs) come in two styles:

  • “Conventional” or “traditional” CTs have a current output on the secondary wires.  The most common output range is 0-5 amps, but there are also some 0-1 amp CTs out there.
  • “Safe” CTs have a voltage output on the secondary wires.  The most common output range is 0-0.333V, but there are also some 0-1V and 0-2V Safe-CTs out there.

Now this is not obvious, but current-output CTs always need a load attached to the ends of the secondary wires any time the primary conductor (the conductor going through the hole in the CT) has current flowing through it.  If you open-circuit the secondary wires of a current-output CT with current flowing through the primary conductor, very high voltages (thousands of volts) can be produced across the open secondary wires!  Never disconnect the secondary wires from a current-output CT with current flowing in the primary wire!

Safe-CTs, on the other hand, can safely have their secondary wires open-circuited while current is flowing in the primary conductor.  The output voltage will not rise when a Safe-CT is open-circuited on the secondary.  There had to be a reason they’re called Safe-CTs, right?  So it’s perfectly OK to grab the screwdriver and move Safe-CT secondary wires around on the meter terminal block.

One Final Note On the Two Different CT Styles

This note isn’t so much about personal safety as it is about not burning up your power meter by mis-application of CT styles.  Most power meters are designed to accept either 0-5A current-output CTs or 0.333V Safe-CTs, but not both.  Here are the consequences of attaching the wrong style CTs to the meter:

  • Attaching Safe-CTs to a meter with 0-5 amp CT inputs will not hurt anything, but the amps readings on the power meter will be completely inaccurate.
  • Attaching 0-5A CTs to a meter with Safe-CT inputs will destroy the CT input circuits in the meter!  So please, don’t attach 0-5 amp CTs to your Safe-CT meter inputs.

Hot and Steamy Pig Tails! How to Measure the Pressure of Steam Without Breaking Your Pressure Transmitter

Posted on by Kele Inc

So, in checking the specs, the PTX1-06, can read pressure up to 200 degrees Fahrenheit, like most pressure transmitters in the marketplace. But, steam is steam at 212 degrees Fahrenheit. How’s that going to work?

This little piggy says to put a copper extender on a pig tail, and shoot the steam to the side for the best readings. This will also add longevity to the life of your pressure transmitter.

Some installers may try to put the transmitter right over the pig tail, or use a snubber, which is actually designed for water and refrigerants, not steam. We have found that an inexpensive and clever solution is to use a combination of a pig tail with a copper pipe extending to the left or the right of the transmitter. This allows the heat of the steam to dissipate to hot condensate. The steam pressure will push past the water in the pig tail, and still allow you to measure the pressure within the pipe. By allowing the temperature to drop, you will get good readings from the pressure transmitter, while saving the wear and tear on the diaphragm of the pressure transmitter, and keep your warranty valid.

Check out this example:

You have a 30 psi steam line, using a PTX1-06 (0-60 psi pressure transmitter) that you need to monitor the pressure in. Screw the pigtail into the steam line. Don’t screw the transmitter directly onto the end of the pigtail. See the chart below to check how long you’ll need the copper pipe to be for your application. In this example, we’d need for it be approximately 2 inches. That will be enough to allow the steam to cool, and be read by the transmitter.

Tubing Length to Isolate Transducer from Temperature Source

From Data Instruments Reference

  1. The pressure vessel is insulated to limit radiant heat transfer to the transducer. Thus, the major source of thermal input is via the connecting tube.  
  2. The pressure medium has a coefficient of thermal conductivity less than 0.4 BTU/hr/ft2/ft/°F (6 cal/hr/cm2/cm/°C).  This figure encompasses a wide range of liquids and gases.
  3. The ambient temperature around the transducer is 100°F (37.8°C).
  4. The heat-transfer rate (convection) from the tubing to still air is 1.44 BTU/ft2/hr°F (1 cal/cm2/hr°C).

If you are blowing through pressure transmitters, they aren’t lasting as long as they should, or giving you false and inaccurate readings, try this, and see if that works better for you.

What’s the Real Difference Between CO and CO2?

Posted on by Kele Inc

In the past few years, there has been a lot of media attention brought to carbon monoxide (CO), as well as carbon dioxide (CO2) and their affect on occupied spaces and indoor air quality. Both are colorless and odorless gases that can have a negative impact on building occupants. However, be sure you know what sort of activity is happening in the space to accommodate the most appropriate sensor.

A Kele Product Manager states it simply, “CO is a car and CO2 are people.” He tells a story about moving into his new home this spring and discovering that the previous homeowner had installed CO detectors in the attic, right next to the electric water heater and the electric HVAC unit. Umm…someone watched the morning news! “Keep your family safe and make sure you know if they are at risk for high levels of carbon monoxide in your home.” Some consumers, out of misinformation and fear, install them in their homes and businesses to protect their families and visitors from this deadly colorless and odorless gas. However, many could have saved their time and money. Carbon monoxide will not be present in a space unless there is incomplete burning of various fuels, including coal, wood, charcoal, oil, kerosene, propane, and natural gas. Therefore, the electric equipment in the attic didn’t need those detectors. The types of equipment that could produce CO include any equipment powered by internal combustion engines such as cars, portable generators, lawn mowers, and power washers. So, a wood shop or environment in a garage with gas-powered equipment running throughout the day would need CO detectors installed. In environments that only have electric equipment, like our product manager’s attic, actually don’t. Oddly enough, we have had reports that many local codes actually DO call for CO sensors in unlikely places, like hotel rooms. This has been most often mentioned in the Northeast. As always, check your local code books for what is mandatory in your area.

More often, in the building automation industry, your customers will be in need of a carbon dioxide detector in occupied spaces such as classrooms, offices, meeting halls or auditoriums. It’s an old science, but demand controlled ventilation has proven the front-runner for saving costs and efficiencies in keeping occupied spaces comfortable with CO2 detection. Please see the comparison of methods for controlling indoor air quality below:

As you can see, in looking at the orange line, which indicates the flow of persons in the space, the CO2 sensing method most closely mimics their occupancy of the space. It’s been the preferred method for controlling the air mix for so long, you may have never stopped to consider what other alternatives a company might have, other than just setting the thermostat for particular hours of business or running it full blast all of the time.

As you’re engineering and installing these systems, take a moment to check out this quick checklist borrowed from ASHRAE (the American Society of Heating, Refrigeration and Air-Conditioning Engineers), to make sure you are in compliance with the ASHRAE Standard 61.1-2010 and 2012 IECC for occupant density spaces, and take these into consideration while planning your jobs.

This next table below lists the default occupant densities by occupancy category from the 2012 IMC and ASHRAE Standard 62.1-2010 for high-density occupancies. Greyed areas are blank where the category exists in one ventilation standard and not the other. Greyed areas with numbers show the values from separate “referred to” or similar category groups in the same standard.

So, as a reminder, CO most likely won’t be in an office space, and unless you’re hosting a sardine party in your garage, you won’t need to sense CO2 there.  In the words of our Kele Product Manager,“CO is a car and CO2 are people.”

Q: The intrinsic safety spec I’m reading calls for an isolated ground. Isolated from what?

Posted on by Kele Inc

Answer: A true isolated ground is not connected to any ground that can ever carry fault current from unrelated parts of the electrical system. It is best to run it directly to grounded building structural steel, an underground metal water pipe, or a separate grounding electrode from the building electrical service as described in Article 250 of the National Electrical Code. However, many grounds that claim to be “isolated” are actually just separate wires run back to the ground bar on the nearest panelboard.  At best, they are run all the way back to the service entrance ground. In either of these cases, a high-current ground fault in the electrical system can raise the potential of the ground wire to destructive levels. True isolation is important for sensitive electronic devices, and is especially important in intrinsically safe systems where an explosion could result from a high voltage appearing on a ground conductor.

Temperature Sensor Curve ID Numbers

Posted on by Kele Inc

 

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)

 

Time Delay Relay Functions Explained

Posted on by Kele Inc

Understanding the differences between various time delay relay operations such as On-Delay or Interval can be a bit confusing.   These simple diagrams may make it easier to visualize what’s happening during the timer operation(s).

 

 

 

 

 

 

 

At Kele, our goal is to make product selection and usage as easy as possible.  Hopefully these simple diagrams make On-Delay, Off-Delay, Interval and One-shot time delay relay functions easy to understand.

Extend Your Reach with the ST-A Series by Precon

Posted on by Kele Inc

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.

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!

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