Why Three Phase Power Should NOT Be Used for Smaller Heaters
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Introduction
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:
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- Three Phase. All of the three wires are used to carry power to the heater.
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- 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.
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- 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:
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- more expensive
- more complex
- less reliable
Written by Jim Dixon
Edited by Shelby Reece
Date Published: 05.02.2018
Last Updated: 09.06.2019