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Dual Voltage Heaters

Why Users Should Almost Never Use Dual Voltage Heaters

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Home > Blog Archive > Category: Industrial Heating Technology > Why Users Should Almost Never Use Dual Voltage Heaters

What are Dual Voltage Heaters?

diagram of Thermal Corporation dual voltage mica band heater

Some heaters are designed to operate from more than one voltage. These are referred to as Dual Voltage heaters. One of the voltages is always twice the other voltage, such as 240 volt/480 volts. These heaters have three terminals or wires. The terminals are connected one way for 240 volts and another way for 480 volts. (Inside are two separate heaters. For the smaller voltage, the heaters are connected in parallel. For the larger voltage, the heaters are connected in series.)

What are the advantages?

These heaters offer an advantage to OEM manufacturers when building equipment. By using these heaters, the OEM can put Dual Voltage heaters on the equipment without knowing which voltage their customer will use. If they did not use Dual Voltage heaters, they would end up building the equipment for one voltage and then if their customer wants the other voltage and they would have to change all the heaters. With these heaters, the OEM just provides documentation on how to connect up the heaters for each voltage. Thus, many heaters shipped on OEM equipment are dual voltage heaters. Dual voltage heaters are more complex and cost more than single voltage heaters, but still make sense for OEM manufacturers.

Failed Heaters

When the equipment is installed at the customer’s facility, it is connected to the appropriate voltage. Eventually one of these heaters fails. Now, what should the replacement heater look like? Should it be a dual voltage heater? Usually, when then equipment is installed, the voltage very rarely changes. Now, in this case, a heater of similar configuration but operating only from a single voltage should be used. Many times, the failed heater is taken to the purchasing agent and the agent is requested to buy a heater just like this heater.

Conclusion

If a user purchases a dual voltage heater rather than a single voltage heater, the dual voltage heater will be more expensive, more non-standard, more complex and because of the complexity, have a shorter life. So for a lower cost and a more reliable heater, order a single voltage heater rather than a dual voltage heater.

Looking for a specific heater? Click one of the links below to browse our product line.

Cartridge Heaters

Mica Band Heaters

Strip Heaters

Rectangular Band Heaters

Ceramic Band Heaters

Thermocouples & RTDs

Custom Heaters

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 05.09.2018
Last Updated: 09.06.2019

photo showing a Thermal Corporation RTD and a Thermal Corporation thermocouple

How Do You Tell a Thermocouple From an RTD?

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Home > Blog Archive > Category: Industrial Heating Technology > How Do You Tell a Thermocouple From an RTD?

photo of a thermocouple and rtd with labels

Some thermocouples look very similar to an RTD. There are, however, usually some small differences. You usually can’t just replace a thermocouple with an RTD without making some changes, such as, reprogramming the controller for a different type of temperature sensor.

The Clues to Tell the Difference

There can be several clues as to whether you have a thermocouple or an RTD (Resistance Temperature Detector). For example, if the temperature sensor has three leads, the sensor is an RTD. Thermocouples only have two leads. On the RTD with three leads, almost always two of the leads will have one color and the third lead will have another color.

For a two wire RTD, usually both leads will be of the same color. For a thermocouple, the two leads will always be of different colors.

(Click here to view our thermocouple color codes/conductor combinations and characteristics chart!)

The “Gold Standard” Difference

The “gold standard” for determining whether a sensor is a thermocouple or is an RTD is to measure the resistance using a Volt Ohm Meter. If the sensor has two lead wires, measure the resistance between the two leads. If the sensor is a thermocouple, you are just measuring the resistance of that length of wire. You would probably measure a few ohms. If you are measuring an RTD, you are measuring the resistance of the wires plus the resistance of the RTD element. For the plastics industries, this RTD element is almost always 100 ohm at 0 0C. At room temperature, this element will read more like 105 to 110 ohms. Thus, if we are measuring an RTD, the ohm meter will read a few ohm more than 105 to 110 ohms, certainly much greater than just a few ohms like the thermocouple would.

If the sensor has three leads, it will be an RTD. There will be three combinations where the resistance can be measured. Two of the leads go to one side of the RTD and the third lead goes to the other side of the RTD element. Thus, two of the reading will read 105 to 110 ohms and the third will read just a few ohms.

If there is a plug on the sensor, a white plug will be an RTD, a black plug will be Type J thermocouple and a yellow plug will be Type K thermocouple.

Looking to order a thermocouple or an RTD? Click here to go to our thermocouple & RTD configurations page.

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 10.23.2017
Last Updated: 09.06.2019

photo showing a close up of the 3 phase option on a Thermal Corporation mica band heater

Why Do We Have 3 Phase Industrial Heaters?

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Home > Blog Archive > Category: Industrial Heating Technology > Why Do We Have 3 Phase Industrial Heaters?

close up image of the 3 phase option on a Thermal Corporation mica band heater
3 Phase Option on Thermal Corporation Mica Band Heater

Introduction

We have 3 Phase electric power because of economics. It is just more economical to produce electricity as 3 Phase Power. If we generated single phase electricity, the voltage changes as if follows a sine wave pattern and the power to generate the voltage would change also. This changing power or torque is not an efficient way to convert mechanical power to electricity. If we generate the power as 3 separate voltages, each voltage wave form is one third of a revolution apart (120 degrees), the power or torque to generate the electricity is constant. That is, the sum of the voltages and the torque as a function of time remains a constant. This makes the conversion of power to electricity very efficient versus having the power be required to change 60 times a second. Also, the vibration created by a varying torque, increases the wear on the bearings and other parts of the generator, a further economic savings. Just about all utility company power, grid power, is generated as 3 phase power, even all of the 120 volts power in our homes.

We have Three Phase Industrial Heaters for 2 Reasons:

  1. By carrying the power to a heater with 3 wires rather than 2 wires, each wire carries less electric current. This means you can use smaller, less expensive wire. A water analogy would be that if you are carrying less water in a pipe, you can use smaller pipes. You should only use 3 Phase power for larger heaters, say above 2000 watts and especially above 5000 watts. If you use 3 Phase Power for small heater, it will be a more expensive heater and possible a heater with lower reliability.
  2. For 3 Phase Power, the larger the currents, (as in a large non- 3 phase industrial heaters), the more heat is produced in the connections inside the heater. Connections are one of the main areas that generate failures. If a connection weakens some with time, the heat produced in the connection will be equal to the current squared times the resistance of the connection. Basically a high currents in the heater generally means a less reliable heater.

Looking for our products? Visit our Products page to view our complete product line of industrial heaters, and industrial heating equipment and accessories!


Written by Jim Dixon
Edited by Shelby Reece
Date Published: 06.22.2014
Last Updated: 09.06.2019

photo showing a close up of the 3 phase option on a Thermal Corporation mica band heater

What is Wrong with this Band Heater Request?

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Home > Blog Archive > Category: Industrial Heating Technology > What Is Wrong with This Band Heater Request?

close-up image of three phase option on mica band heater

The Band Heater Request:

4.5″ Diameter x 1.5″ Wide, 480V/3 Phase, 700 Watts

Introduction

Virtually all industrial power is generated as 3 Phase power. At the generating plant, it is generated as three phase power, because it is MUCH more economical to generate power as three phase. The power is then transmitted as three phase power. Just look at power transmission lines. You always see the lines in sets of three. Sometimes the heaters use all 3 phase voltages and sometimes they use one phase of the power. A single phase heater can run off of one of the phases of the 3 Phase power, connected either between two of the phases or between one of the phases and a neutral return path (0 Volts).

Why would you want to build the band heater as a 3 Phase heater?

You want to build a band heater as a 3 Phase heater to reduce the current in the wires going to the heater. When you carry the power through three wires rather than the same power through two wires, the current is less. Why do you want the current to be less? Higher current requires larger wire which costs more. Also, failures frequently occur where connections are made and the higher the current in a connection, the greater the likelihood of a failure. Some of these connections are inside the heater.

Generally, you can start considering making the band heater a three phase heater when the total wattage gets in the range of 2000 watts. You probably should make the band heater a three phase heater when the wattage reaches 5000 watts and almost definitely be a three phase when the heater reaches 10,000 watts.

So, what happened?

What happens sometimes is that someone is told that the heater will be running off of three phase power. That does not necessarily mean the heater has to be a three phase heater. All single phase power comes from three phase power. The question is how much is the current or wattage? In the heater we are talking about, the current is 700 W/480 v = 0.69 amps. Thus, even connecting the heater as a single phase heater, the current is 0.69 Amperes. This is just a little more than a 60 watt light bulb. Making this band heater a three phase heater would make the current even less. A three phase heater is more complex to build than a single phase heater. Thus, there are more things that can go wrong and it cost more. Why choose a heater that is more expensive and less reliable?

In Conclusion…

All power starts out as three phase power. Just because the power source is three phase does not mean the heater has to be a three phase heater. To answer the question, does the heater need to be three phase, look at the current or wattage. Don’t order a heater as a three phase unless it really needs to be one.

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 10.30.2017
Last Updated: 09.06.2019

small sheath

What is a Split Sheath Cartridge Heater?

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Home > Blog Archive > Category: Industrial Heating Technology > What Is a Split Sheath Cartridge Heater?

So, what exactly is a Split Sheath Cartridge Heater?

photo of a Thermal Corporation split sheath cartridge heater

Spilt sheath cartridge heaters are tubular heaters that have been formed in to a half circle which is then folded in the middle with the two halves now making a circle. Their claim to fame is that they are easier to remove from a hole. This is true – but more on this later.

The drawings that usually accompany the advertisement show the two halves expanding as the heater heats up with the heater more completely filling the hole. The amount of expansion is actually a function of the thermal expansion of the metal sheath. Different metals expand different amounts, but all of the expansions are rather small, at least compared to the drawings, which are exaggerated for clarity. All of the sheath materials are either one of the stainless steels or incoloy steel.

closeup photo of a Thermal Corporation split sheath cartridge heater

The main point here is that a split sheath cartridge heater will expand the exact amount as a regular cartridge heater made of the same steel. The amount of expansion is a function of the thermal expansion of the sheath and the diameter of the heater, which is the same for both types of heaters. Thus, they are the same.

Ease of Removal

While it is possible to manufacture a heater in a near perfect circle, when you form the circle into a half circle it is not a near perfect half circle. When you put the two halves together, the resulting shape is slightly football shaped. That is, the diameter in one direction is not the same as the diameter if you rotate the measurement by 90 degrees. The difference is something on the order of 0.015 to 0.020 inches. What this means is that the AVERAGE diameter is smaller than a regular cartridge heater. THIS is why it is easier to remove. The smaller the diameter the easier the removal.

Disadvantages

With a slightly football shape, the heater is not making as good of contact with the hole and thus poorer heat transfer. The internal temperature of the heater will be higher and the heater will have shorter life.

Also, tubular heaters have more magnesium oxide insulation between the element wire that generates the heat and the inside of the sheath compared to a regular cartridge heater. This means the heater can more likely be run in air because of the higher breakdown due to the thicker MgO, but also means that this thicker insulation reduces the rate of heat transfer. Again, poorer heat transfer means that the heater will have a higher internal temperature and resulting shorter heater life.

Edited by Shelby Reece
Date Published: 07.19.2018
Last Updated: 09.09.2019

Should Your Heaters Be Wired in Parallel or in Series?

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Home > Blog Archive > Category: Industrial Heating Technology > Should Your Heaters Be Wired in Parallel or in Series?

Should your heaters be wired in parallel or in series?

So, should your heaters be wired in parallel or in series? This question comes up when there is more than one heater to be connected to power. Basically any number of heaters can be connected in parallel, but usually only two heaters are connected in series. Connecting more than two heaters in series becomes much more complicated. With heaters connected in series, if a heater fails it can affect the other heaters. With heaters connected in parallel, the failure of one heater usually does not affect the other heaters.

The Most Common Pairing

The most common pairing is usually a two piece heater. In this case, if the heaters are connected in series, the voltage of each heater must be equal to half the total voltage available. For example, two 240 volt heaters connected in series across a 480 volt supply. Also the wattage of each heater must be equal. (If the wattage and voltage of each heater is not equal, the heaters will not split the total voltage equally.) If the two heaters are connected is parallel, the voltage of each heater must be the same as the supply voltage.

So, Why Choose One Way Over the Other?

One reason is that some heaters may not be able to be built as reliably at one voltage. This has to do with the physical dimensions of the heater, and the watts and volts. Basically you want an optimum element wire ( the wire that gets red hot) size in the heater. In some heaters, because of close spacing, the heater may not be able to be built at 480 volts. Also, if you wire in series, the failure of one heater most likely affects the other heater.

Conclusion

Remember, in parallel, each heater has the same voltage, but in series, each heater has the same current. Basically, you only wire in series when you have two heaters of equal wattage and voltage. In most other cases, you wire in parallel.

Looking for our products? Click here to view Thermal Corporation’s complete line of industrial heaters and industrial heating accessories.

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 07.20.2014
Last Updated: 09.06.2019

electrical drawing

Case Study #176: When Increased Watt Density Causes Poor Heater Life

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Home > Blog Archive > Category: Case Studies > Case Study #176: When Increased Watt Density Causes Poor Heater Life

Case Study #176

A customer contacted our engineers a while back about an issue they were having with an industrial heater that was getting poor life.

The Case:

The customer said he was using 480V 3-phase power and was bringing out two legs. He had been using a heater rated for 600W at 240V. The power that was actually applied to the heater was 277V, but he was getting poor heater life.What was going on?

diagram showing the application of the 3 phase heater

The photo above is a diagram of the two lines he was bringing out. The customer was applying 277V to a 600W 240V heater.

What was the actual wattage generated?

The formula below described to our engineers what was happening.

new wattage equals old wattage times new volts squared over old volts squared 600 times 277 squared over 240 squared equals 800 watts

Conclusion

So, in this case, he was actually generating 800W, which is 1/3 more wattage than the original designed wattage of 600W. The watt density was increased by 33% also, hence the shorter life.

Written by Jim Dixon and Shelby Reece
Edited by Kyle Otte
Date Published: 06.19.2019
Last Updated: 11.21.2019

heating drawing

208 Volts Is a Weird Voltage. Where Did It Come From?

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Home > Blog Archive > Category: Industrial Heating Technology > 208 Volts Is a Weird Voltage. Where Did It Come From?

Three Phase Power

Three phase power has several parts that could be classified as “weird”.

Three phase power is power that comes in on three separate lines. In each line, the voltage follows a sign wave pattern. Each wave is similar except they are out of phase. By that, we mean that the second wave begins at the point where the first wave is a third of the way through its cycle. Then, the sine wave for the third line begins at the point that the first wave is two-thirds through and the second wave is now a third of the way through its cycle. This is just like singing the song Row, Row, Row your Boat gently down the stream, in three rounds, with each part starting at a different point in time.

three phase power

Each of the three power lines is hot. A load can be place between any two of the hot line OR between one of the lines and neutral ( a return path for the current that is at “0” volts.) If you place the load between two of the hot lines, one can be a positive voltage while the other is negative. This means that the voltage between them can be greater than the voltage from one of them to neutral (volts)

3 phase 4 wire in y

208 3 Phase DELTA

FIRST IMAGE IS 3 PHASE 4 WIRE in “Y”, SECOND IS IN DELTA

208 volts 3 phase

Line-to-Line Voltage

When we talk about the voltage between two hot lines, we call it Line-to-Line Voltage. When we talk about the voltage between one of the lines and neutral we call it Line-to-Neutral Voltage. The Line-to-Line voltage is always greater. And there is a constant ratio between the two. The Line-to-Line Voltage is always 1.732 times the Line-to-Neutral Voltage. (The 1.732 is the square root of 3). Unless we specify otherwise, when we say three phase we are talking about Line-to-Line Voltage.

Conclusion

Now to get back to our question. 208 volts is Line-to-Line Voltage. This three Phase voltage is frequently used in small businesses. Why? Well, what is the Line to-Neutral Voltage for this. It is 208 volts /1.732 which is 120 volts. The power is brought is as 208 volts 3 Phase and then the Line-to-Neutral Voltage will be 120 Volts. Each of the three Line-to-Neutral line will go to a part of the plant. When the lines were installed, the plant was divided into roughly 3 equal area from a power usage standpoint, with one line going to each area. This way, these areas have 120 volts to run their equipment from.

Looking for our product page? Click here to view Thermal Corporation’s complete product line of industrial heaters and industrial heating accessories.

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 08.07.2017
Last Updated: 11.21.2019

photo of the 3 phase option on a Thermal Corporation mica band heater

Tips for Extending the Life of Band Heaters

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Home > Blog Archive > Category: Industrial Heating Technology > Tips for Extending the Life of Band Heaters

image of a mica band heater

#1 Avoiding Contamination

Both mica band heaters and ceramic band heaters are vulnerable to contamination.

  • Moisture is one of the most immediately noticeable contaminants. If sufficient moisture is present at start-up, the heater fails as soon as power is applied. Sometimes, when the heater has been cool for a prolonged period and has been subject to a high humidity environment, there will be enough moisture absorbed to cause failure at start-up. When insulated lead wire has gotten wet near the heater, the moisture can be wicked into the heater and cause failure. Anytime heaters fail as soon as the power is supplied, moisture is a strong suspect as the culprit.
  • Oil and other organics can cause heater failure if they get inside the metal sheath, but they behave differently than water. Most oils and organics do not conduct electricity very well as lower temperatures, but carbonize and become conductors at elevated temperatures. Thus, if such contaminants are present, the failure occurs only after the heater has gotten hot enough to cause carbonization. Like water, oil that gets on the lead wire insulation can be wicked into the heater.

#2 Avoiding Over-Temperature

  • A loose fit of the band heater on its cylinder will reduce the heater’s lifetime because the heat generated is not transferred efficiently to the cylinder being heated, causing the heater to run at a higher temperature to transfer its energy. The higher the operating temperature, the shorter the lifetime. It is good practice to retighten the clamping strap or clamping tabs after the first time that the heater has been used, because the heater will be better conformed to the cylinder during its first heat-up. Anything that prevents a smooth fit of the heater on the cylinder, such as a cylinder surface irregularity, will shorten the life of the heater because the net effect of the irregularity is to make a “loose fit” in spots.
  • Choose the lowest wattage heater than will maintain the desired operating temperature of the cylinder being heated and still provide a short enough start-up time. Choosing a heater with higher wattage than required will result in the controller turning the heater on and off to maintain the desired temperature and a higher operating temperature during on-time. These conditions will shorten the heater life.

#3 Excessive Cycling

  • The way that Thermal Corporation evaluates the lifetime of their own band heaters and those from competitors is to cycle the units from 150°F to 900°F and count the cycles to failure. Cycling reduces lifetime because the surface of the element wire oxidizes rapidly at higher temperatures; if the higher temperature is maintained, the oxide coating actually protects the wire from further rapid oxidation, but if the wire temperature is reduced substantially, the oxide coating breaks off due to contraction and exposes fresh metal to more oxidation. With continuous cycling, the wire diameter is eventually reduced, and the resistance of the element is increased to the point that it becomes too hot. At that point, the element wire either melts and breaks open the circuit, or it causes the insulation over the wire to break down, causing a short to the sheath.

#4 Physical Abuse

  • Never carry a band heater by the lead wires. If the heater has post terminals, use two wrenches; one to hold the bottom nut and one to do the tightening on the top nut.

Edited by Shelby Reece
Date Published: 07.05.2018
Last Updated: 09.06.2019

thermocouple junctions

Thermocouple Junctions & Their Importance

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Home > Blog Archive > Category: Industrial Heating Technology > Thermocouple Junctions & Their Importance


There are three different types of junctions for thermocouples: exposed, grounded, and ungrounded. Each of these serves a different purpose and has different characteristics. Let’s look at each type of junction and where they should be utilized.

What Are Thermocouple Junctions and Why Are They Important?

Briefly, a thermocouple works utilizing the Seebeck Effect. The Seebeck Effect is the conversion of thermal energy into a voltage potential at the junction of different types of metals. If a continuous circuit is made using dissimilar metals joined at two junction points, and the two junction points are at different temperatures a small voltage will flow through the wire. By measuring this small voltage (usually tens of millionths of a volt), we can determine the temperature at the place where the two dissimilar metals are joined (the junction). The thermocouple junction is, therefore, extremely important because this is the point where we are actually measuring temperature.

Exposed Thermocouple Junctions

As depicted in the picture to the left, exposed junctions consist of two bare wires that are joined outside of a protective metal probe. Exposed junctions are used to measure the temperature of a gas. Because there is no protective cover, the junction is very fragile. No moisture, or liquid or solid contaminants should be present in the gas. Exposed junctions, however, do provide a faster response time because thermal energy does not have to travel through a metal sheath and/or compacted insulation to impart energy to the junction.

Grounded Thermocouple Junctions

Grounded junctions are the most common type of junction. In this application, the junction is connected directly to the probe tip usually via soldering or welding. This provides a relatively fast response time as heat only has to travel through a metal sheath or probe and weld, all of which have a high thermal conductivity. This also provides durable protection for the junction inside the probe tip.

Ungrounded Thermocouple Junctions

Ungrounded junctions are used to protect sensitive electronics from small feedback voltages. Ungrounded junctions are similar to grounded junctions in that they are inside of a protective probe. However, they are not welded or soldered to the probe tip; instead, they are surrounded by an insulator, usually magnesium oxide. Ungrounded junctions provide a slower response time because heat must travel through the probe tip and then through the magnesium oxide (which has a lower thermal conductivity than a metal) before reaching the junction.

So, Why Have an Ungrounded Junction-type Thermocouple?

One reason for an ungrounded junction-type thermocouple is if there is a small voltage difference between grounding points. For example, an electronically-sensitive control panel is grounded at 0V. This instrumentation is connected to a temperature sensor that is on a machine which has a small voltage leak through the ground circuit and thus is grounded at 1V. There exists the possibility that a small current could travel through the sensor back to the control panel and have an unwanted effect on the electronic equipment.

Main Points

  • Each junction is useful for different types of applications.
  • Exposed junctions have no protective cover and are very fragile.
  • Grounded junctions are the most common junction type and have a fast response time due to the highly thermal conductive material.
  • Ungrounded junctions are surrounded by an insulator and provide a slower response time, but are useful for protecting sensitive electronics from small feedback voltages.

Written by Kyle Otte
Edited by Shelby Reece
Date Published: 02.01.2019
Last Updated: 09.04.2019

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