Dave Weigel, Chief Engineer

About Dave Weigel, Chief Engineer

Kele’s UL Panel Shop: Your Source for Meeting Code

Did you know that when you assemble power supplies, controllers, relays, transmitters, and all that other stuff into an enclosure for your control panel, there’s a rule in the NEC that requires your panel to be listed and labeled as an industrial control panel?

Article 409 of the NEC is devoted to the installation of industrial control panels, which are defined as an assembly of two or more components consisting of:

  1. Power circuit components only, such as motor controllers, overload relays, fused disconnect switches, and circuit breakers;
  2. Control circuit components only, such as pushbuttons, pilot lights, selector switches, timers, switches, control relays; or,
  3. A combination of power and control circuit components.

Articles 100 and 110 of the NEC further insist on listed and labeled equipment where such safety standard exists. An informational note in Article 409 refers the installer to UL 508A as an example of a suitable safety standard for industrial control panels. Kele’s UL 508A panel shop can fulfill your needs for a listed and labeled industrial control panel. Send us those drawings in whatever format you choose, and we can help make your panel conform.

So what is UL 508A all about? It’s all about safety – safety from fire, and safety from personal injury. The standard stipulates everything from enclosure type to wire size. There’s a lengthy part about proper separation of power circuits from Class 2 circuits. There are standards that must be met for every part installed in the panel that is upstream of Class 2 circuits. There are labeling requirements for many different scenarios. There are requirements for overcurrent protection and short circuit protection. In sum, a UL 508A panel is a safe panel.

Why Kele? Our UL Panel shop is authorized by UL to list and label your panel as meeting UL 508A standards. Our staff is regularly trained, and a UL inspector makes sure that our work is up to snuff.

We have recently added an additional 1,800 square feet to our panel shop, for a total of 6,720 square feet.

This means we have the capacity to handle your largest projects.

See below for some pictures. We currently have 23 people on our Panel Team with over 150 years on combined experience in BAS/panel building. We’ve also added a new Panel Review Team that will inspect all panel drawings before the panels are moved into production to eliminate any issues or questions plus a Panel Shop Manager, Lisa Bennett, who will make sure your panel is built to spec, on-time and tested before it ships to you, ready to install.

Call Bennie Crowder today at 888-397-5353 or email us at panels@kele.com to get your control panel UL listed. We’ll build it up to the standard, test it, and ship it to you ready to install. Our normal lead time for building panels is 2 weeks or less plus there is an expediting option for quicker shipment.  For more information on our panel shop, please visit http://www.kele.com/panel-shop/.

Repeat / NSTA Panel Assembly Area

Custom Panel Assembly Area

Inspection / Pack Out Area

Controls and Cables in Environmental Air Handling Spaces, Ducts, and Chases

First, let’s discuss controls and their enclosures in air handling spaces, ducts, and plenums. Many times, we have to install items in these spaces and it’s important to consider that anything we put in there should either be non-combustible (metal) or else be listed under UL 2043 for use in air handling spaces.

The NEC is what governs this requirement.  Section 300.22(C)(3) states that, “Electrical equipment with a metal enclosure, or electrical equipment with a nonmetallic enclosure listed for use within an air handling space and having adequate fire-resistant and low-smoke-producing characteristics, and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other space unless prohibited elsewhere in the code.” An informational note included in the code defines UL 2043 as a permissible standard for such a nonmetallic product.

Not many plastic items meet this requirement, so it’s best to stick with metallic enclosures. The purpose behind this limitation is that we don’t want smoke to spread via the air handling systems in the event of a fire – and we certainly don’t want that smoke to originate inside the air handling system.

UL 2043’s title is Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces. Anything combustible (that is, not metal) installed in an air handling space should be listed to this UL standard. Confusion comes in when products have been listed to other flame test standards.  A product listed as flame-spread tested to UL 94 V-0 or UL 94 H-2 is NOT the same as UL 2043, and does NOT indicate that the product is suitable for use in air handling spaces. Some inspectors will accept these flame-spread ratings, but of late that number of inspectors is dwindling. They want to see “Plenum Rated” and UL 2043 is the only standard available at this time to apply such a label. UL 94 is a test for flammability only. Smoke is the key to safety in air handling spaces.

So what’s the do-all solution?  Use a metal product, or put your plastic product in a metal box.  It’ll never be questioned by an inspector.  Temperature sensors like the Kele KT-D and Precon ST-D are all available with metallic wiring boxes (XH or XW options).  Humidity sensors like the KH-D and HD-20K have metal wiring boxes as well.  Stick with these when in-duct or in-plenum mounting is essential.  Of course, if in-duct or in-plenum mounting is not essential, don’t mount it in there!

Now let’s have a look at wiring in air handling spaces and chases. If not in metal conduit, there is a wide range of choices for low-voltage cabling – plenum and chase ratings have been around much longer than UL 2043, so manufacturers have made listed cables for every application. The important thing to take away from this article is that there are two very different ratings available.  Plenum rating is one, and chase (riser) rating is another.  Be certain that your cable is marked and listed for use in plenums and/or risers as appropriate. Substitutions may be made according to Table 725.154(G) in the NEC.  In general, plenum rated cables can be used in risers, but not the other way around.  Kele’s Model CBL carries both CL3R and CLP3 ratings and thus can be substituted for almost any application.  Here’s a copy of Table 725.154(G), courtesy of the National Fire Protection Association. It illustrates the hierarchy of Class 2 and Class 3 cable types allowed in various spaces:


  • CL3P = Class 3 Plenum
  • CL2P = Class 2 Plenum
  • CL2R = Class 2 Riser
  • CL3R = Class 3 Riser
  • PLTC = Power Limited Tray Cable
  • CL2X = Class 2 Limited Use
  • CL3X = Class 3 Limited Use
  • CL2   = Class 2 General Purpose
  • CL3   = Class 3 General Purpose

Remember, as professionals in the building automation industry we are a part of the team that is charged with preventing the spread of fire and smoke in buildings. By paying attention to what we install in plenums, ducts, and riser chases, we can insure the safety of those who inhabit our buildings.

When the Controls Just Won’t Work

I have an old engineer friend I’ll call Bucky (not his real name). Bucky was burned years ago when he designed an HVAC system that turned out to have insufficient capacity to keep the building comfortable in winter. In fact, the perimeter offices were in the low 50s (°F) (low teens °C) when the first cold snap hit. When I say he was burned, I mean it figuratively – but the occupants of the building were thinking about burning him literally.

Well, old Bucky was not going to be burned again. We joke that the architect has to specify stronger door hardware when Bucky is doing the mechanical design, so that the doors don’t blow off the hinges from his absurd supply air quantities.

This leads to a control problem on Bucky-designed jobs. I had to install and program a building automation system for a Bucky job, and it wasn’t a good experience. How can one tune an office temperature control loop when the reheat box can warm the room faster than the temperature sensor can respond? The occupants would essentially be subjected to supply air temperature, which could reach 130°F (54°C) in heating mode.

I first went with my tried-and-true PID tuning method that I learned from a DuPont instrument engineer in the early 1980s. This method had never failed me until I tried it on Bucky’s HVAC system. I worked for a couple of hours on a single office but I could not get anything near stable control. I tried adding a feedforward loop to give the PID loop advance notice that the oversized hot water valve was about to open. That took programming time and it didn’t help at all.

So I went back to the office and batted the problem around with a group of my peers. We discussed, we calculated, we got out our controls books. We came to no good conclusion.

The next day, I programmed all of the interior spaces with no problem. There was way too much air but my tuning method resulted in stable control on the first pass. Then I went to ponder the perimeter offices again. As the building was approaching occupancy time, the painters were gone and the carpets were being installed. There happened to be a carpet layer in the office I went to first. I thought out loud for a minute, then I vented to him about what a pain the air system was for me. He sat up on his heels and listened, then said, “Seems to me there ought to be a way to reduce the air and water flows.”

I turned mighty red with embarrassment at that time. I thanked the carpet layer and went to call the test and balance fellows. They agreed to cut back on the water and air to the perimeter spaces if I could convince Bucky that I needed it. Well, Bucky came to the job site and it was pretty easy to convince him by getting him to stand in a perimeter office for a while. Problem solved, but not by me. They say that if your only tool is a hammer, then every problem looks like a nail. That was my problem in a nutshell. I was a controls guy, so I focused only on the controls.

The lessons I learned were: 1) Engineers can be wrong (yes, really!); 2) When a system can’t be tuned, the system might need fixing; and, 3) When all else fails, ask the carpet guy.

Humidity Sensors in Distress

Let’s start with a riddle:

Q: They’re dirty, they’re annoying, they cause all sorts of trouble, they make everyone uncomfortable, and they’re hard as heck to catch; but, they’re not the pesky flies that buzz around one’s picnic potato salad? What are they?

A: Humidity sensors abused by hostile environments.

You’d be surprised where we find hostile environments. They’re not always in industrial plants and oil fields. At one point, the office in which I sit was a hostile location. On occasion, it still is. Read on.


Believe it or not, humidity can be hostile to a humidity sensor. That is, humidity is hostile when the moisture in the air is allowed to condense into liquid water on the surface of the sensor or its electronics.

Any time an object’s surface temperature is below the dew point of the surrounding air, condensation will form on the object. If the object is exactly at the dew point or just a degree or so below it, a fine mist will form all over it. If the object is much colder, say 10°F (5.6°C) or more below the air’s dew point, a fully wet surface and active dripping will be the case. To prove the latter case to yourself, take a frosty cold can of your favorite soda outside on a muggy summer day and observe the puddle wherever you set it down.

So how is this hostile to a humidity sensor? After all, being wet is just the same as 100 percent relative humidity, right? Wrong. When we say 100 percent relative humidity, we mean that the air is holding all of the water vapor it can hold at a given dry-bulb temperature. We use the term saturated air for this condition, and it is a special point at which the air’s dry bulb temperature is equal to its dew point temperature. Humidity sensors handle that just fine. Saturated air does not necessarily mean that the surfaces of things are wet. In fact, is unlikely that a humidity sensor or its electronic parts are wet because they each dissipate a little bit of power; this power warms them, so their temperatures should be a little bit higher than the surrounding air; their surfaces should be above the dew point temperature, so they should stay dry.

When a sensor gets wet, it will typically give a 100 percent humidity output. But it takes a while for it to dry out even after the surface condensation evaporates. Think of a humidity sensor as a tiny sponge. The liquid water that it has soaked up will take time to wick to the surface and evaporate even if drying conditions are good. If drying conditions are poor (high humidity), the time can be very long. Some sensors dry more quickly than others, but they all take time.

When the sensor finally gets dry, it has a new component to it. While water condensed from the air is pretty clean, it’s not perfectly pure. It leaves some residue on the surface from which it evaporated. One bit, or even a dozen, may not affect the accuracy of the sensor. Regularly repeated exposure to liquid will make those tiny bits of residue add up to a coating around the sensor that can seriously shift its calibration.

So what makes them wet, then?

Unusual conditions can cause a humidity sensor and its electronics to be colder than the dew point of the surrounding air, and there are also conditions in which other objects above the sensor get cold and drip condensation down on it. Here is an example, along with the solution that was employed to get proper humidity sensing back on track.

The Sensor is Blowin’ in the Wind…

The most prevalent occurrence of condensation indoors is when the humidity sensor lies within a room’s supply air stream during summer months in humid climates. One example came from a specialty retail store that required pretty good humidity control in its showroom. The store is located in a city with consistently humid outdoor air. Sorry, the names of the store and city are omitted to protect the innocent.

This store had supply air diffusers designed to discharge air across the ceiling at enough velocity that it did not fall until it reached the wall. Thus, anything mounted on the wall at the falling point can be considered to be sort-of in the supply air stream. That’s where this store’s humidity sensor was mounted. Unfortunately, it was also mounted fairly close to the store’s front door. On warm, humid days, the outdoor air would swoosh in when a customer opened the door. Also unfortunate was that the humidity sensor was directly in the path of that swoosh of warm, humid air. So, the sensor would be nice and chilly and then get hit with a blast of air with a dew point much higher than the sensor. This collision of warm humid air with the chilled sensor created instant wetness. Worse, it went on all day long, every day.

Not only did this poor sensor read 100 percent most of the time in the summer, it also was toast after only six weeks in place. When it was opened, it was obvious what had happened. The sensor element and all of the electronics were covered in a fine layer of dust. The contractor relocated the sensor toward the middle of the store, out of the way of any supply air and out of the way of the incoming air from the front door. The sensor then gave proper, accurate readings instead of bouncing up to 100 percent all day. It also lived happily ever after. It’s two years old at the time of this writing.

Corrosives and Other Nasties

The bulk of this article is about condensation because it seems to be the least understood of the humidity sensor enemies. Corrosives and other foreign substances (volatile organic compounds or VOCs) are more obvious destroyers, but some of them have sources that are not so obvious.

Silicones are the most surprising hostile substances for humidity sensors in general. Many instances have been reported in which silicone sealant has been used to caulk around an installed outdoor air humidity sensor’s wiring box or conduit body. A few indoor sensors to our knowledge have been attacked by the use of silicone sealant behind the sensor to insulate it from the wall cavity. One trouble with silicone sealants is that they emit the volatile part of the goop as it cures. The volatile part is typically a hydrocarbon solvent – not good for the innards of a sensor element. These vapors can shift the sensor’s calibration a bit. Repeated exposure can shift the calibration a lot. Another trouble is that uncured silicone sealant itself can spread rapidly over surfaces both by wicking and through air. This substance can shift the calibration of a humidity sensor by 2 percent to as much as 10 percent. If a sensor must be installed with the use of silicone sealant, wait until the silicone cures before installing the sensor. Even better would be to use an alternative like latex caulk.

Corrosives are harder to deal with. Some commonly encountered sources of corrosives include swimming pools, paints, paint strippers, solvents, wood preservatives, aerosol sprays, cleansers and disinfectants, moth repellents, air fresheners, stored fuels, automotive products, hobby supplies, dry-cleaned clothing, and personal care products. All of these things emit volatile organic compounds (VOCs) that are not friendly to humidity sensors and their electronics. As the term corrosives implies, these particular VOCs eat away at the sensing element and uncoated parts of their electronics.

When corrosives attack on a regular basis, the sensor will usually shift calibration slowly until it suddenly dies completely. A corrosion-resistant sensor can weather the attack and prolong the time between replacements. Some (very expensive) sensors are nearly immune to such corrosion and are typically found in industrial or laboratory environments.

Other Stuff can treat humidity sensors badly. For instance, plain old dust is very common. The effect of a routinely dusty environment will be a delayed response time that worsens as the dust gradually coats the sensing element. After totally enclosing the element or filling the elements filter, the output of the sensor’s response time will be so long as to present a steady output to the reading device or controller. One solution for dust is to place the sensor in an aspirated box with a washable or changeable filter.

Notes on Filtering: Some humidity sensors include a gas-permeable filter such as Gore-Tex® that does not allow passage of liquids or solids. That can be a big help in keeping the bad things away from the sensing element. It won’t stop condensation that occurs inside it from humid air, and it won’t stop corrosive gases. It will keep the sensor safe from dust, drips, and rain. The filter might require occasional cleaning, though. Sintered metal filters do a good job with particulate matter and an OK (but not perfect) job with dripping water or rain. They, too, may require occasional cleaning in dusty environments.

So how did my office become hostile to a humidity sensor?  Let’s just say it involved a hot plate, some Indian food (chicken tikka masala), an office neighbor with a sensitive nose, and two cans of Lysol spray.  I’ll leave the rest up to your imagination.  My humidity sensor was a gone…


Ways can almost always be found to mitigate the effects of condensation, corrosives, and other nasties in the air that attack humidity sensors. The tough part is knowing what they are in advance. The easy part is calling Kele Technical Support at 877-826-9045 for assistance in winning your sensor’s battle against these elements.

Are You Sure You’ve Checked Everything?

Late one afternoon not long ago, a fellow got me on the phone for tech support. He said he had ten carbon dioxide transmitters on one DCP-1.5-W power supply, and they weren’t operating, and he had pulled out most of his hair. Each transmitter needs less than 100 mA to operate, so the 1.5A power supply should have been more than enough.

He had applied power to the transmitters one by one, and all was well until he connected the fifth unit. At that point, the voltage dropped from 24 volts to 6, and it continued to drop bit by bit as he connected additional units. He checked everything, he said—he even powered up each individual unit directly from the power supply—and they were all just fine. What to do?

After receiving his wiring diagram by e-mail, I called him back and asked him to hook up all ten units as shown on his diagram so that he could test each point while on the phone with me. With his voltmeter negative lead alligator-clipped to the power supply negative, he started measuring voltages. At the power supply positive, he called out “24.” At his 115SP terminal strip, he called out “24” again. Going down the strip, he called out “24” four more times, at each of the first four connected units. At the fifth terminal, he called out “6,” and added, “See what I’m talking about?”

Now, this fellow is an old hand—I didn’t have any reason to doubt his ability to strip a wire and hook it to a terminal—but there was no denying the voltage was going away at that one point. So after a minute’s thought, I said to him, “The terminal showing 6 volts has two screws, right? Humor me and check them both.” After a short debate, he agreed, and he found that the missing 18 volts was being dropped across what appeared to be a perfectly good wiring terminal! He replaced the terminal strip next, and his system was ready for commissioning.

The next afternoon, he called me back to say that he was so curious about that terminal that had caused him such grief that he got his die grinder out and removed the terminal’s plastic insulation. That’s when he discovered that the internal bus was cracked all the way across— it was just luck that it was making enough contact to show 6 volts on its downstream side.

Strange but true! The lesson I learned was this: before we claim to have checked everything, it’s a good idea to broaden our definition of “everything.” Wires can be broken in the middle, terminals can be cracked—it only takes a second to check, and it might make the difference between a good night’s sleep and a frustrating all-nighter.

When Electricity Acts Up

This past weekend, we were just back from a trip to market, and my wife was busy stowing the fruits, veggies, oils, kimchi, and spices. I was doing my usual chore of qualifying and sorting the plastic shopping bags as to fitness for cat litter duty, kitchen waste duty, and “other,” based on leakage potential. I’m sure all of you engineers out there know the drill, so I won’t belabor it. Since this is a simple test routine that requires very little thought (as long as the cat’s asleep), my mind wandered into the realm of strange electrical anomalies, as my mind tends to do at such times…

Having just finished up researching an article on instrument isolation practices for conditions in which “ground” may not be the safest place to touch during a lightning storm, I got to thinking of other instances in which the normal means of protecting electrical circuits can be outflanked by Mother Nature. I recalled one episode of returned product from a customer whose 30A relay contacts, socket, and screw terminals had all obviously been subjected to extremely high current. The relay armature had melted and burned violently, while the contacts were welded together. The whole thing was a black, charred, mess. We were unable to reproduce such damage with the largest load that we could throw on it at the time.  We could make it pop and sizzle, and eventually it would fail at 60A – but not in a blaze of glory like the ones returned to us.

Why did the customer return them to us in the first place, if they had obviously been subjected to fault-level currents, which would certainly not be a warranty issue? The 20A circuit breaker upstream of the relays did not trip during this event! In fact, the circuit that appears to have unleashed all of its fury on the poor little relay remained intact and continued to power other, non-controlled loads as if nothing had happened. Our customer wanted us to help determine the trouble – and more importantly, give him some advice to keep it from happening again.

After several rounds of questions and the review of e-mailed pictures, building drawings, and wiring diagrams, we were finally able to determine that this relay was controlling a lighting circuit. It was composed of one long row of fluorescent fixtures at the ceiling level of a warehouse, and at the end of the row it poked out through the wall and also powered one outdoor area light that was mounted on the uppermost corner of the building. One more question brought closure. Was there a thunderstorm that day?

The energy of a lightning strike is immense, we all know that. What was unusual about this situation was that the energy of the strike originated at the end of the circuit, traveled back upstream toward the power source, and caused the control relay to become the fuse that saved the rest of the equipment on the circuit from disaster! In burning the contacts and armature of the relay, enough energy was expended that the next device upstream (a 20A circuit breaker) didn’t need to operate – and the remainder of the lighting branches that were tapped off upstream of the relay suffered no damage. Remember, lightning doesn’t always send us trouble down the electrical wires from the source – sometimes it sneaks in the back way.

We’ve seen some strange ones during our long careers, and we’ll post ‘em here from time to time for everyone’s enjoyment (engineering enjoyment, that is). Perhaps it’ll help one day when one of our customers runs into an electrical problem that just doesn’t seem to follow the rules.