Dan Grinley

Stainless steel and its related superalloys are exceptional materials known for their resistance to rust, particularly when operating at room temperature or below. However, their resistance to oxidation diminishes when exposed to heat, although they still exhibit impressive resistance. This is why stainless steel and incoloy are preferred materials for the outer sheaths of our heater product lines.

When subjected to heat, the outer layer of our heaters’ material oxidizes as the iron combines with oxygen from the surrounding air. This oxidation process, commonly known as rust, can be advantageous. As stainless steel oxidizes, its surface changes color, providing a visual indication of the temperature it has reached.

Here’s a table illustrating the color changes stainless steel undergoes at various temperatures:

There are countless articles on-line describing the two varieties of 3-phase power systems and why one is more beneficial over the other based on your application. The 3-phase systems are called 3-phase delta and 3-phase wye and this document will explain how to connect your single phase heaters to such a system, and more importantly, how to check that it’s done correctly with a few simple resistance measurements.

First, you’ve got to determine the type of system you’re working with. If your electrical system has no neutral wire, you’re probably working with a 3-phase delta system where the legs of the system are connected in a triangle. Delta gets its name for the Greek upper case letter delta (Δ) which resembles a triangle. If you do have a neutral wire, you’re probably working with a wye system. Just think of the letter Y because all the lines are connected to a central node. It’s good to confirm the type of system you have by checking an ID plate or other documentation you have regarding your 3-phase system. The use of the word ‘probably’ above is used because there are exceptions to every rule. Though rare in the case of 3-phase power systems, it’s still best to check. If you have three heaters of equal resistance you’re ready to go. If you have six heaters, that’ll work too. Any multiple of 3 heaters is what you need in these types of systems.

For a 3-phase wye system with three single phase heaters, connect one lead of each heater to the central node and the other lead of

each heater to one of the 3-phase nodes. If you have a multiple of 3 heaters, connect them in equal groupings in parallel. Maybe a few diagrams will help.

As you can see the 3 nodes for each leg are labeled A, B and C, which is typical. They might be labeled 1, 2 and 3. In a 3-phase Wye configuration you have the fourth node that’s labeled N or Neutral.

When checking that you’ve connected the heaters correctly you should measure the resistance between each leg (A, B and C) and

the Neutral leg. They should all measure about the same, within the resistance tolerance of the heaters you’re using. You should also check the resistance from leg to leg. Check from A to B, A to C and B to C. Each resistance across those connections should be double that of a single leg, again, within the resistance tolerance of the heaters. When you take those measurements, you’re measuring the resistance of two legs connected in series, ignoring the third (unmeasured) leg. The term ‘single leg’ or ‘leg’ is used instead of a heater because there might be multiple heaters in parallel across each leg. Just make sure you know the resistance that should be present on each leg.

If R is the resistance for a single heater, and P is the number of heaters in parallel you have across each leg then the total number of heaters in your setup should be 3 x P and the resistance from each A, B or C to N should be R/P.  The resistance from A to B, A to C and B to C should be 2 x R / P.

If you check your system and all the resistances are as described you can be very confident that everything is wired correctly.

When it comes to a delta configuration, the math is a little tricker and it’s easy to see why. There’s no neutral node so the resistance checks must be made between nodes A, B and C. In that case you’re measuring a single leg which is in parallel with the two other legs that are connected in series. Connect your single phase heaters as shown in the diagrams below, depending on the number of heaters you’re using.

Sparing you the trouble of how to calculate the values, you should read the resistance of one leg divided by 1.5 or R / 1.5 where R is the resistance of one heater when using one heater on each leg . In other words, if you have three 50Ω heaters connected in a 3-phase delta configuration you should measure 33.3Ω from A to B, A to C and B to C.

When there is more than one heater connected in parallel on each leg of a 3-phase delta configuration, the resistance between a pair of legs is R/(1.5 x P) where R is the resistance of a single heater and P is the number of heaters in parallel on each leg.

Six 150Ω heaters in a 3-phase delta configuration where there are 2 heaters connected in parallel on each leg should give you a resistance of 50Ω from A to B, A to C and B to C.

In a crazy example of 18 heaters measuring 650Ω each, in a 3-phase delta configuration, the resistance between legs should read 650/(1.5 x 6) = 72.2Ω.

To Summarize, using R as the resistance of a single heater and P as the number of heater connected in parallel on each leg of a 3-phase circuit,

…..the resistance across any two nodes of a 3-phase wye configuration is 2 x R / P.

…..the resistance across any two nodes of a 3-phase delta configuration is R / (1.5 x P).

One additional thing to watch out for in a 3-phase wye system that must be mentioned is the voltage present across each leg. If the 3-phase system is labeled as a 480V 3-phase wye system, the voltage across each lead is only 480/√3 or 277 volts. Whatever a 3-phase wye system may be labeled (call it V), the heaters are going to be subjected V/√3 or V/1.732.

That’s not the case in a 3-phase delta system. A heater across a leg of a 480V 3-phase delta system will be subjected to 480 volts. There is no adjustment necessary with a 3-phase delta system.

This should help you to be able check your 3-phase wye or delta configuration with confidence.

When you need to determine the wattage required to heat an application, you can delve into some nitty-gritty details when it comes to calculating that number. If you have a good temperature controller, you’re safe to overestimate that number and still be okay, resulting in a system that reaches the desired temperature without the need for lengthy calculations.

Presented here are a few quick ways to determine the wattage requirement for different scenarios. You don’t have to worry about heat loss via convection and radiation or concern yourself with other aspects of the calculation.

To heat something by a certain amount, you just need to know the type of metal you’re heating, its mass, the change in temperature required, and how quickly you want to get it to temperature. Based on the type of material, you’ll look up a coefficient for the material being heated that goes into a simple equation, and you’re off!

The equation looks like this:
Wattage = Material Coefficient x Lbs of Material x (Desired Temp – Starting Temp [in °F]) / Hours to Get to Temperature

Here’s the table of coefficients for some common materials:

The equation above, using the numbers from the table, calculates the wattage requirement for heating the mass to temperature and then adds about 40% on top of that. The additional wattage is enough to account for the heat losses to the environment that would occur. The Material Coefficient number is just a modified Specific Heat of the material to give the wattage calculation that extra boost.

Here are a few examples:

1) Let’s say you have a sealing platen weighing 24 lbs that you need to get to 300°F from room temperature (72°F) in 30 minutes. It’s made of stainless steel.

The solution to the equation above is: Wattage = .05 x 24 x (300-72) / 0.5 = 547.2 watts. Call it 550 or 600 watts to play it really safe. That’s how many watts you need (presumably in electric heaters) to heat your platen from room temperature to 300°F in about half an hour. You can drill a few holes parallel to the face of the platen and insert cartridge heaters that will produce 600 watts.

2) You have a large outdoor circular aluminum trough weighing 50 lbs filled with 80 lbs of water that you need to get to 70°F from a cold condition of 40°F, in an hour.

This solution requires using the equation twice; one for the aluminum trough and one for the water. For the trough itself the equation is 0.100 x 50 x (70-40) / 1 = 150 watts. For the water the equation is 0.420 x 80 x (70-40) / 1 = 1008 watts. Add those two together and you get 1158 watts in total. Round that up to 1200 watts and you should be good to go. The heat can be applied either by wrapping the trough with a large band heater or by heating the base with inserted cartridge heaters. Either way, get 1200 watts into the system and you should be able to get it to temperature in about an hour.

That takes care of heating solids and liquids with an easy estimation that will get you working well enough. When heating air, a couple of other equations are used, depending on whether the air is compressed or not. That’s a story for another Ask Ian. If you have a complex application that needs more attention to determine the wattage requirements, please contact Tutco and we’ll be glad to help.

There are normal variations in the dimensions and electrical properties of heaters we build, and it’s good to know what they are so there are no surprises.

First, a few words about tolerances in general. Tolerances are deviations from nominal values, be they lengths or resistance values, in the case of our heaters, that are deemed acceptable. Tolerances exist because of variations in manufacturing processes. Nothing can be manufactured perfectly the same way every time. If you measure closely enough (to enough decimal places), you’ll always find a difference between two manufactured parts. Some tolerances are present because of things that we do in the process, like swaging, and others are passed on to us from suppliers that we have to live with, like the resistance tolerance of a spool of resistance wire, measured in Ω/ft.

Varieties of Tolerances we’ll cover in this article are: Length, Wattage, Resistance, Diameter, Width, Leadwire Lengths, Protection Lengths, and Camber.

Length: Starting off with Hi-Temp Cartridge Heater lengths, the tolerance of a swaged cartridge heater length is ±2% of its length or 1/8”, whichever is larger. For example, the length tolerance of a 12” long heater is 12” x 0.02 = 0.24” or about 1/4”. For a 3” long heater, it would be 3 x 0.02 = 0.06”. Since 1/8” is larger than 0.06”, the tolerance on that heater is 1/8”. The reason for that tolerance being length-dependent is because of the swaging operation we perform on every heater. There’s a small amount of uncertainty as to the exact length heaters will swage to due to there being so many variables in the components of what is being swaged. That variability results in heaters that, when built and assembled identically, result in slightly different final lengths. That tolerance of ±2% of the length accounts for that variability.

For Standard Cartridge Heaters (unswaged, loose fill heaters), it’s a lot easier. The tolerance of the length of those heaters is ±1/16” regardless of the heater length. The reason for that is because we have a lot more control over the heater length. Since the heaters aren’t swaged, there’s no change in their length during our processing and no predictions of the final length are required. What you cut (to length) is what you get, and we can cut tubing to a precision of 1/16” over a heater of any length. The same applies to Ceramic Strip Heaters, Ultima Strip Heaters, and Permaheat Strip Heaters.

For some band heater and other strip heater dimensions, we have similar control as with Standard Cartridge Heaters. What you cut is what you get. For heaters with widths <=4”, the tolerance of that width is ±1/16”. For heaters over a 4” width, you’re looking at a tolerance of ±1/8”. That applies to HT Mica Bands, Better Bands, HT Mica Strip, and Better Strips.

The ID tolerance on band heaters, in general, isn’t as much of a concern, nor is it as easy to specify because there’s spring-back when it comes to forming the ID of a band heater. If your heater clamps around your object properly and clamps tightly in place without the gap shrinking to 0”, then you’ve got a good fit.

Wattage and Resistance: Now we move to an electric property of all heaters. When you purchase a heater at a certain wattage, say 1000 watts at 120 volts, there’s a variance on that wattage of +5%/-10%, meaning the wattage could vary from 1050 watts down to 900 watts. The variance actually resides with the resistance where the resistance tolerance is +10%/-5%, which translates to the aforementioned wattage tolerance when a known voltage is applied. The reason for the overall variance is because of the variance in many of the materials we use, along with the processes performed to make your heaters. There’s a tolerance of ±5% of the resistance (in Ω/ft) in the plain resistance wire we purchase. There’s a variance in the winding process that puts wire around a ceramic core or piece of flat mica. There’s a variance in the amount of resistance change when a heater is curved to shape or swaged to diameter. Variances stack up, so we end up with a final resistance range of 15% around the nominal value, whether you’re talking about wattage or resistance. We really build resistance devices where we can tell you the wattage you’ll get when a certain voltage is applied. We control the resistance as best we can, and knowing the voltage you’ll be applying, we can determine the wattage you’ll get out of the heater, along with the tolerance of that wattage. Why is the wattage tolerance +5/-10% instead of ±7.5% if the tolerance range is 15%? We do that to be on the safe side. We would rather have a heater operate with a lower wattage than one that’s much too high.

Can we do anything to make the tolerance smaller? Yes, but it’s not inexpensive. Sometimes the only way we can do it is by sorting. Finished heaters that do not conform to the tighter tolerance are simply scrapped and built again. That drives up costs, which are then passed on to the end customer. We could also attack the problem further up the production stream by asking our suppliers to provide parts built to a tighter tolerance. Guess what happens? The costs go up. There’s always a trade-off, and no such thing as a free lunch.

Diameter: Changing gears again, when it comes to cartridge heater diameters, we size our heaters to an ideal heater size that’s slightly undersized to fit into a hole it’s intended for, along with a tolerance. For example, a 1/2” diameter hi-temp cartridge heater is actually provided at a 0.495” diameter with a tolerance of 0.002”. The heater is named after the hole it fits into, not its actual size. Due to tool availability, it’s a lot easier for a machinist to drill a 0.500” diameter hole than a 0.505” diameter hole, which would be required if we provided a heater at 0.500” in diameter. And besides, “a 1/2” diameter heater” rolls off the tongue a lot more easily than “a 0.495” diameter heater.

Here are lists of diameters for the two varieties of cartridge heaters.

TUTCO can provide a wide variety of heater options for many of our product lines. Some of those lesser known but very useful options are distributed wattage heaters, zoned heaters, and dual voltage heaters. They allow for better performance and better control over heaters so you can get the most out of them. 

Distributed Wattage heaters are built to provide different amounts of heat over different sections of a heater while applying voltage to a single set of leadwires or screw terminals. A wattage distribution can be built into most types of heaters though it is most common in cartridge, band and some strip heaters. The purpose of the distributed wattage is usually to attain a better temperature profile (more even temperature) due to sections of a heater exhibiting greater heat loss than other sections.

Winding of resistance wire inside a heater is arranged so that it will produce different wattages over different lengths of the heater (in the case of cartridge heaters) or different wattages over different areas (in the case of band or strip heaters). 

In the case of cartridge heaters, the ends are naturally cooler than the center of the heater, and applying the right wattage distribution to the heater can make the temperature more consistent over a longer length of the heater. The evenness of this temperature profile is most important for sealing applications where an even temperature is required across a sealing bar to provide a good melt across the material being sealed. The more even the temperature profile, the faster the sealing process can operate, which many customers want. There are some common wattage distributions that work in most cases. We call them 35-30-35 and 40-20-40 meaning that the heated length is split into three equal lengths and each section produces 35%, 30% and 35% or 40%, 20% and 40% of the total wattage. Those ‘hotter’ ends of the heater lead to a more even temperature profile. There are plenty of other distributions that a customer may want and they’ll specify the unique wattages and lengths that they’re looking for. 

In the case of band heaters, a hole might be present in a heater to avoid a large bolt or some other obstruction. That obstruction might pull an excessive amount of heat from the heater thereby lowering its temperature near the hole. A distributed wattage can ‘fix’ that by putting more wattage around the hole, thereby producing a heater that generates heat with a more even temperature profile. 

As the name states, a distributed wattage heater is a heater where wattage has been distributed or ‘moved around’ so the heater can provide the best performance for your situation. Zoned heaters are used when you want to be able to control different sections of a heater independently. There are a few different types of zoned heaters. They can be designed as cartridge heaters, most band heaters, and a few types of strip heaters.

In instances when there are two zones, there are typically 2 sets of leads (or screw terminals) where a set consists of two leads, so there are four leads in total. You could consider a band heater built with a flexible hinge option to be a zoned heater if it’s a continuous single heater yet has two sets of screw terminals or leads on either side of the gap. Those zones are operated independently in the same heater. 

With cartridge heaters it can be a little tricker, but in most cases a heater with four leads can be produced and it gives you two zones to control independently, where the heating occurs at each end of the heater. 

If you want a three-zone cartridge heater, that’s more of a challenge but still something we can offer. Due to the nature of the internal components of a cartridge heater we can only design it with 4 leads exiting at most. In that case, one of the leads would be a common lead, and the other three leads would be there for each zone. To control ‘Zone A’ in Figure 3, you would apply voltage from the Common Lead to the leadwire labeled ‘Zone A’. To operate Zones B and C, you would apply voltage between the Common Lead and the corresponding leadwire. All three zones can be operated simultaneously, and independently.

It should be noted that a three-phase power source cannot be used with this type of heater because you cannot adjust the voltage of each leg of a 3-phase power source, nor turn any of them off independently.

Zoned heaters give you the options to control separate sections of a heater as if they were their own separate heaters.

Dual Voltage heaters are built so that they can operate at one of two voltages and produce the same wattage over the entire length of

the heater in both scenarios. A bit of clever wiring is how we build
these types of heaters. This is helpful if a heater will be operated in the US and Europe and the customer needs to be able to account for that, by a simple wiring change. Dual voltage heaters (as either cartridge or band heaters) are built with 3 leadwires or screw terminals and voltage is applied either between only two of the connection points, ignoring the third, such as 1 and 3 in Figure 4 below or to that third terminal (2) and the other two terminals (1 and 3) connected together. It should be noted that dual voltage configurations are only possible when one voltage is exactly twice or exactly half of the other voltage. 110V/220V is a good combination, as is 230V/460V, but something like 110V/230V or 230V/480V is not possible.

For situations where you need to account for your applications being operated by possibly two different voltages, consider using a dual voltage heater.

As you can see there are several electric configuration options available that you may not be aware of or may have never taken advantage of. Consider the options available when you want to get the best performance out of your heaters.