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Railcar Heating

For nearly 50 years, we have developed electric heaters and controls for railcar systems. For overhead, sidewall, floor or cab heating needs, we have the experience and proven solutions.

Open Coil vs. Finned Tubular Design

Advantages of Open Coil

No Secondary Insulation

Indeeco's open coil design eliminates the need for secondary electrical insulation. The coil and terminal insulators provide the necessary electrical creepage for up to 800 volts (Figure 5). Finned tubular elements must be mounted on secondary insulators, as the insulation between coil and sheath is not sufficient to meet this spec.

Reduced Weight/Quicker Response

Open coil elements are lightweight in comparison to finned tubular. For railcar heating, a typical open coil element weighs one ounce per foot, allowing it to reach operating temperatures rapidly and cool down quickly when de-energized. The open coil's response time is substantially less than a finned tubular heater (Figure 6). This results in more accurate temperature control, since the open coil responds more quickly to changes in environmental conditions.

Withstands High Temperature

Open coil elements can withstand substantially higher temperatures than finned tubular elements. Grade A resistance wire (80% nickel, 20% chromium), which Indeeco uses exclusively, can operate continuously at 2150º F. Although elements in railcar heaters are designed to operate in the black range (approximately 1200º F maximum), this margin of safety means that element burnout is virtually unknown under normal conditions. Furthermore, since the alloy is all nickel and chromium, atmospheric corrosion is eliminated. Even finned tubular elements built entirely from stainless steel will begin to corrode at elevated temperatures.

Withstands Over-Voltage

In railcar applications, the maximum operating voltage is typically 20% higher than the nominal voltage. Since wattage varies as the square of the voltage, these heaters must be designed with a 44% safety factor. Simply by varying the gauge of resistance wire used in an open coil element, the safety factor is achieved. Finned tubular elements, by contrast, do not have this flexibility. To meet a 44% safety factor, 44% more element length must be used. Often, space for this additional length is not available due to tight quarters in the overhead compartment.

Low Pressure Drop

Because of the high percentage of open space across the heater, open coils have low pressure drops when compared to finned tubular heaters. Figure 7 shows pressure drops for both constructions and for an open coil with pressure plate attached. (In the railcar application, the cooling coil acts as a pressure plate, so a separate pressure plate is not required.)

Eliminates Thermal Expansion Problems

As finned tubular elements heat up and cool down, their length increases and decreases. This constant movement can create element wear and distortion, leading to field service problems. Open coil elements, on the other hand, behave quite differently because of their helical shape. As the element heats up, the pitch of the helix decreases slightly (i.e. there is less space between turns) and the coil goes back to its normal shape as it cools down. Open coil elements are designed with at least one wire diameter between turns, substantially more than adequate expansion room.

Withstands Voltage Spikes

Open coil elements are not subject to damage due to high voltage spikes. Finned tubular elements, on the other hand, must be isolated from grounded metal to prevent arcing through the thin layer of magnesium oxide insulation separating the coil from the sheath.

Proven Reliability

Open coil railcar heaters are extremely reliable. They have been in the field for at least 30 years.

Advantages of Finned Tubular

Elements Withstand Physical Abuse

Finned tubular elements are more rugged. That is, if the element itself will be subject to physical abuse, finned tubular elements are preferable.

Insulated Coils

If the element is exposed to human contact, open coils should not be used. The reason is obvious: Open coils are electrically live, whereas finned tubular elements have the coil electrically isolated from the exposed sheath.

Overhead HVAC Heater

Finned tubular elements are mounted in a stainless steel frame, which in turn is mounted to the HVAC overhead unit using weld nuts in the frame's flanges. Element terminals are ceramic-insulated. Support brackets are isolated with an insulating board. The entire element assembly can be removed for servicing without disturbing the heater frame.

Thermal Cutout and Fusible Link

An automatic reset thermal cutout, mounted in the top flange, can be serviced with the frame in place. A fusible link assembly, mounted on the leaving air flange, provides secondary thermal protection.

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