We had a call from a customer questioning how to calculate what the current would be for each wire in 3-phase band heater. Here is the band heater breakdown: 480V, 3,000W, 3-phase. The heater looked something like the diagram you see below.
Inside this heater, it was wired in a “wye” configuration. The wye configuration wiring diagram would look like:
The resistance of each winding card inside the heater is equal, giving us a balanced load. Therefore, each phase will handle 1/3 of the load. 1/3 of 3,000W is 1,000W. 480V is the voltage between the 3 phases (line to line). The voltage between any phase and the ground (line to ground) is:
Now that we know the wattage and voltage in each leg of the 3-phase power, we can calculate the current.
Current = Watts / Volts = 1,000W / 277V = 3.6 Amps in each leg
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Written by Jim Dixon Edited by Shelby Reece and Kyle Otte Date Published: 10.07.2019 Last Updated: 10.08.2019
A customer called in and wanted to know what amperage he would be using on a machine with six heaters. The power supply was 460V, 3 phase power, and the heaters were wired in a delta configuration with two heaters on each branch. (See image below)
To Determine the Amperage:
6 heaters (R1 – R6) each at 230V, 1,000W
The resistance of each heater is calculated using the following formula:
R = V2 / P
So, the resistance of each heater equals 2302 / 1,000 = 52.9Ω
R1 = R2 = R3 = R4 = R5 = R6 = 52.9Ω
Now, we wire two of these heaters in series between two legs of 460V, 3 phase power. Each leg looks like:
In series, we can add resistances and simplify the circuit to look like this:
Now, finding the current is easy.
I = V / R I = 460V / 105.8Ω I = 4.35A
So, the amperage is 4.35A for each leg.
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Written by Jim Dixon and Shelby Reece Edited by Kyle Otte Date Published: 07.11.2019 Last Updated: 09.03.2019
When power is generated, it is almost always generated as three phase power. This is because it is considerably more economical to generate power as three phase power. (With three phase power, there is a constant torque required for the generating turbine rather than a torque that changes 60 time a second as if we generated single phase power.) Three phase power consists of bringing the power in on three separate lines. Each line will have the same voltage but will be different from the other two. (Each one is shifted 1/3 of a cycle from the other.)
Heaters Can Be Connected in Three Ways:
Three Phase. All of the three wires are used to carry power to the heater.
Single Phase-“Line to Line”. Two wires are used to bring in power. One wire is connected to one of the three phase wires. The other wire is connected to one of the remaining two wires.
Single Phase – “Line to Neutral”. Two wires are used here also. One of the wires is attached to one of the three phase wires. The other wire is connected to neutral (think “ground” or “zero volts”.)
Reasons to Use Three Phase Power
The main reason to use three phase power is to divide the power between three wires instead of between two wires. Less power is now required for each wire. Less power means less current in each wire. For less current, smaller wire can be used. Smaller wire, means lower cost wire. (Don’t be confused by larger wire having a lower gauge number and smaller wire having a higher gauge number.) Also, for lower current, the electrical connections both inside and outside the heater will be more reliable.
A heater needs to use three phase power because the heater is required to produce a relatively high wattage. Even if the ultimate power is three phase, a heater can be connected as a single phase heater as in 2 & 3 above. Generally, up to 2000 to 3000 watts, the heater should be single phase heater. As the wattage increases to 5000 watts, three phase becomes appropriate. By 10,000 watts, three phase is usually required. Since the ultimate power source is always three phase, customers sometimes assume the heaters must be three phase. The heater should be three phase only if the wattage is high enough for it to be appropriate.
Conclusion
In conclusion, three phase heaters are more complex to manufacture. Making a small heater to be three phase means it will be:
more expensive
more complex
less reliable
Written by Jim Dixon Edited by Shelby Reece Date Published: 05.02.2018 Last Updated: 09.06.2019
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
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.
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)
208 3 Phase DELTA
FIRST IMAGE IS 3 PHASE 4 WIRE in “Y”, SECOND IS IN DELTA
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.
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Written by Jim Dixon
Edited by Shelby Reece
Date Published: 08.07.2017
Last Updated: 11.21.2019
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:
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.
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.
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Written by Jim Dixon Edited by Shelby Reece Date Published: 06.22.2014 Last Updated: 09.06.2019
