3 Phase Electric Duct Heater

3 Phase Electric Duct Heaters 

A three-phase electrical circuit can supply three times the power as a single-phase circuit at the same voltage with only one additional wire.

Commercial and Industrial duct heaters utilize 3 phase electrical power to produce more output wattage per square inch than single-phase electric heaters. Higher voltages result in higher currents and more heat output. With limited cross-section area in heating ducts, higher 3-phase voltage connections are more efficient.

Power distribution basics

Homes in the US have two phase 240 feeds stepped down by a transformer from the power company's 3-phase lines. Voltages vary from the power plant, transmission, and end-user - your home or industry.

Electricity is produced at 30,000 volts and then stepped up by transformers to 66,000 volts and higher for transmission over long distances. The higher the voltage, the more efficient the transfer along the transmission lines.

At the electricity destinations, substations' transformers step down the electricity for local distribution to homes and businesses. These voltages are 16kv, 12kv, and 4kv going to your transformer on a pole or in-ground connecting to your home. Their transformers step down the voltages to 240V 2-phase for homes and businesses.

In industrial and commercial buildings, the transformers step down to 240 - 480 - or 575 3-phase voltage feeds. These three-phase power feeds enable more energy for industrial processes and heating.

More power equals more heat.

Tim, the Tool Man, always exclaims more power equals more work! That is why many of our battery-operated power tools have gone from 6 to 12 volts to 18 volts over time. In addition, each has more amperage output from larger and better batteries.  5

EVs follow the same pattern with bigger and bigger batteries with more current to run their motors faster. The DC voltage from electric car batteries is converted to 3-phase 400 - 800 V AC to power the motors that convert the electrical energy to horsepower.

Using three-phase power in a duct heater offers higher voltage and currents. In addition, the combination provides high power output voltage.

PTC elements offer advantages in three-phase electric duct heaters

Packing a lot of power into small spaces has advantages and disadvantages. For example, traditional resistive heaters connected across one phase of voltage can lead to uneven heating characteristics if the resistive elements don't have matching resistance values or if one burns out.

PTC resistive heating elements used in parallel self-adjust their resistance in response to temperature maintaining a more balanced heat output across the surface of the duct heating element. These solid-state devices are durable, with little chance of burning out over the heater's life.

One big advantage of PTC heaters is self-regulating temperature. If the airflow in the duct decrease or stops, the PTC heaters will not overheat. As the temperature increases due to a lack of airflow, the device's increased resistance limits the output temperature to a predetermined set-point.  

The difference between single & three phase electrical power

The three-phase power supply can handle larger loads than a single phase. In a duct heater, this results in more heat output. A three-phase connection uses one more wire than a single phase when connected in a delta configuration and a fourth or neutral wire in a wye configuration.

Here are links to the calculations and differences between single-phase and three-phase power.

Advantages of 3-Phase PTC Duct Heaters

• High watt density
• Electrical Isolation
• Encapsulated heating elements
• Efficient heat transfer
• Self Regulating 
• Safety & durability
• Balanced Loads

Learn more about how PTC electric duct heaters work.

High watt density distributed across the plenum

PTC heaters combine effective heat transfer with self-regulating temperature control.  

Each phase connection contains multiple PTC solid-state heating elements distributing the heating in a matrix fashion across the aluminum fin structure. As a result, the fins create significantly even heating across the airflow in the ductwork without hot or cold spots.

Electrical isolation, safety & durability

Each PTC heating element is isolated electrically from the aluminum fin casing. At the same time, the elements produce symmetrical heating on both sides of the ceramic disks. In addition, each is clamped into place, prevents damage to the heater, and ensures long-term stability.

Even with the elements electrically isolated, never work on the air heater components without shutting off power to the unit.

No combustion takes place in a PTC heater improving safety around combustibles. Additionally, adding more or larger PTC elements can increase power and voltages.

Self-regulating current and temperature control

The self-regulating characteristics of the PTC heating elements respond to increasing/decreasing airflow. More airflow will produce more heat transfer as the current will increase at lower temperatures. With less airflow, the elements will reduce current as the temperature rises within the heating matrix.

Insufficient airflow can lead to the deterioration of the devices over time.

Efficient heat transfer with aluminum V-shaped fins.

DBK air heaters are designed in a V-finned matrix with the PTC ceramic discs clamped in series along each cross member. There are six cross members, two connected to each phase of power. This distribution and the air passing through the aluminum fins create a very effective heat transfer mechanism.

Balanced loading

When resistors are connected in parallel there is a chance of unbalanced loading if the resistance of each leg is not identical.  Current will flow to the lowest resistance.  This can create a difference in heat transfer across the surface of the heat exchanger.

PTC heating elements change resistance with temperature.  If one leg of the circuit is receiving more current than the other it will heat faster but as it does the resistance will increase.  This effectively balances the current between the three legs of the circuit.  This is unique to PTC heating elements.

Typical Applications for 3-phase PTC air heaters

You can find these heaters in industrial and commercial applications where airflow needs to be heated efficiently and safely.

• Ventilation systems with heat recovery
• Building climatization & Pre-heaters 
• Industrial HVAC

More detail on specific applications and applicable standards

Information on DBK HRP series of air heaters can be found here.

For specific information on specifications, connecting 3-phase heaters, and power requirements, contact our thermal management engineering department at 864-599-1600.