Kele Blog

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.

Is Saving Energy Really that Hard to do? Apparently it is for Some?

Posted on by Kele Inc

As many of us have been told for years, programmable thermostats are worth their weight in gold when it comes to energy savings. Well, maybe not gold these days, but you get the point. According to the Department of Energy, heating and cooling costs are one of the largest expenses associated with commercial buildings. Savings from using a programmable thermostat can be impressive. Recent studies show that proper usage of a programmable thermostat can cut business’ heating costs by approximately 25%. In the summer, such devices may shave cooling costs 15 to 25%. In fact, according to the Department of Energy, on average, every degree raised on a thermostat in the summer or lowered in the winter, saves 2% on monthly energy spend.

So why is it that so many people are now stating there is no significant savings? That’s quite simple to answer; people don’t know how to program them or just don’t bother to! According to recent information released by the EPA, “Available studies indicate no savings from programmable thermostat installation. Some studies indicate slight increased consumption.” That is quite alarming given that programmable thermostats are supposed to decrease energy usage. As it turns out, they also stated that it is not necessarily the fault of the thermostat itself, but that people don’t use the programming functions properly on their thermostats. Most, according to the study, blame difficulty in programming as the reason for not using the thermostat properly. The EPA found that nearly 90% of programmable thermostats are used like a traditional manual thermostat in which occupants raise and lower the temperatures as they feel the need to change their comfort level. This can drive utility costs much higher than needed for building owners as the temperature setting doesn’t get changed back to a normal setting when people leave the building.

As BAS contractors and HVAC specialists, we certainly know that using a programmable thermostat saves energy. As shown above, it is very expensive to leave the temperature inside an office building constant day and night through the use of a manually operated thermostat. Programmable thermostats allow business owners to make adjustments for energy savings automatically.

So how do we change this trend? The best solution for now is to share the facts and educate your customer. Explain the overall benefits to them, but most importantly don’t just program their thermostat for them and walk away. Make them program it while you’re there and you can walk them through it. Not only does this give them peace of mind, it assures them that you understand the benefits and are looking out for their best interests.

Here are some basic tips you can share with your customers when showing them their newly installed thermostat:

  • When programming the thermostat, keep it set at a constant temperature for long periods of time, such as 12 to 14 hours when the space is not occupied.
  • When closed for a longer period of time such as holidays, set the hold button at a constant temperature. Or, with many of the new programmable thermostats you can set a holiday schedule.
  • Resist the urge to override the settings. Every time that is done it costs money. Installing thermostat guards can help prevent this as well.
  • If you have zoned heating and cooling, install a programmable thermostat in each zone. Especially if you have areas that are not occupied for long periods of time.
  • If your thermostat runs on batteries, change them at least once a year.

As we move into the next decade we face even more challenges when it comes to building automation and energy savings. Wireless technology is upon us and it is making a huge splash in the HVAC industry. Programmable thermostats are no stranger to this shift in technology as there are now many wireless options available. Also, the never ending trend of personalized control from smart phones and remote programming options has become part of most thermostat manufacturer’s standard portfolios. Kele has many of these in our offering and we can help with them as well.

All in all, the trend for most customers when it comes to programming thermostats and planning for energy savings is quite simple…make it simple and make it automated and they’ll follow those plans and guidelines. Well, the manufacturers’ are doing their part by making it automated. It’s up to us to continue to educate everyone to make it simple.

Green Buildings need Clean Electrical Power for Sustainability

Posted on by Kele Inc

Major changes are taking place in the United States as we all move forward to reduced energy consumption and utilization of renewable energy sources in our homes, offices, campus environments, and factories.

As new technology becomes available with ever increasing returns on investment many owners are ready to become part of the “Green Movement” that is currently taking place all across america. No question about it the time is right for all us to move forward with our Green initiatives.

With this in mind it is important to understand the goal here is to save money across all of our operating budgets. The two basic tenets of a green operation are energy efficiency and sustainability. In order for a building, process or product to be truly “green” it must achieve both of these goals.

There are many products and services available today that can dramatically reduce our consumption, improve our efficiencies, and supplement our energy sources. These new technologies VFDs, LED lighting, Building automation Systems, Solar generation, Battery Storage, to name a few all have one thing in common, they affect the the power distribution in our building in many ways. Many times it is a combination of these building changes that begin to interact with each other.

For example, having re-lamped an entire garage with LED lighting retrofits a hospital was pleased with the energy savings they were enjoying until they had failures of the lights due to to power quality issues in the building during generator operations. All of the energy savings were lost due to the cost of replacement electronics.

Sustainability of the equipment in our buildings is highly dependent on the Power Quality within our buildings. Many repairs or glitches within our systems can be traced back to power quality issues when adequate Power Quality Monitoring is done.

In the past it has been an expensive time consuming effort to have power quality surveys done in the buildings. Most cases these were done after the fact when problems had already caused major disruptions and equipment failures. This reactive method of understanding the Power Quality Dynamics of our building may have gotten us by years ago, but with all of the new changes taking place a more proactive real time Power Quality Monitoring Solution is needed.

The ability to install powerful “Real Time” Power Quality Meters with alarming functions and data collection is now highly cost effective and key to maintaining sustainability of our buildings. These PQUBE Power Quality meters are like the Black box recorder on an aircraft. They sit within the electrical cabinets and switchgear monitoring Power Quality 24/7 in real time.

Once an event is detected they generate alarms and reports as to what the event was, how long it lasted and most important they identify their location which is critical in understanding our buildings operations.

Taking only 30 min to install, and no software to learn the PQubes are the most cost effective and useable Power Quality Meters to date. Their small footprint (about the size of your hand) allow them to be retrofitted into existing electrical panels, transfer switches, and switchboards at many locations within your building.

As we make these major investments in green technologies it only makes sense that we know our buildings Power Quality, real time, all the time. PQube Power Quality meters put you ahead of problems before they become disasters.

Kele Services

Posted on by Kele Inc

Often times when people think of Kele they think of our huge product selection and availability. It’s true—not only does Kele provide nearly 60,000 products to choose from, we also have unlimited access to hundreds of thousands of product SKUs from over 300 of the industry’s premier manufacturers. But did you know that Kele has several services that could help drastically simplify your projects and workload? Here are some of our most used services:

1. Custom Panel Fabrication

Kele has been building custom panels for over 30 years and is an expert in panel layout, specification and assembly. We are here to help with your panel fabrication needs by providing parts for enclosures/panels from our $10 MILLION INVENTORY. Not only do we have the inventory to support your custom panel needs, we also thoroughly review all panel designs, perform quality control testing on every panel and have a short lead time. We stay flexible and our panel assembly team builds quality, tested panels to meet YOUR DEADLINE.

2. Custom Valve and Actuator Assembly

Kele’s Production Shop removes the guesswork from tedious product assembly. Most orders are assembled and shipped the same day—a free service to you from Kele. We offer the largest selection of valve and actuator brands in the business. In our custom valve assembly shop we can get your electric or pneumatic actuators professionally installed on our wide variety of 1/2″ to 6″ ball, zone, and globe valves. We also provide free tagging for easy identification when they arrive at your jobsite.

When it comes to customized assemblies, Kele also offers a wide selection of pressure transmitter assemblies with bypass valves, gauges and enclosures for protection during startup and maintenance, as well as protection against the environment. We also offer a variety of light assemblies for controls components, indicators, and labeling to make your peripheral components installation and maintenance easy.

3. Custom Calibration Solutions

At Kele, we use precision calibration equipment to set your specified signal ranges and engineering units. Most orders are calibrated and shipped the same day. Calibrated products include: differential pressure transmitters, temperature transmitters, output transducers, flow transmitters, power supplies, isolators, lighting contactor initiators and much more. Need help connecting your calibrated devices to the automation system—no problem. Our technical support team is available for any troubleshooting needs you may have.

4. Technical Experience

The whole idea of Kele started with the unique needs of BAS engineers and contractors in mind—an idea that has grown into 30 years of outstanding customer service and unmatched technical support. In fact, our client-facing, technical team has a total of 350 years combined experience.

One Source Solution

Kele’s entire business model is founded on the concept of providing a ‶one-stop solution”—where not only can you get EVERYTHING YOU NEED FROM ONE SUPPLIER, but have it shipped to you quickly and know that you have the technical support when you need it most. That’s why we not only provide our customers with the best product selection and availability in the industry, but we also offer several valuable services to help our customers simplify and streamline their projects.

For more information on the services Kele provides, please visit us on Kele.com or call 1-877-826-9045.