Electric Cable and Radiant Heater Installation Guide
1. Purpose and Scope
This instruction applies to installations of electric cables and radiant heater folios with voltages of 300/500 V, embedded in floors and roof slabs. The UNE 21,155 -1 standard indicates the types of heating cables that can be used. Both these folios and radiant heaters must conform to the requirements of the directives stated in Article 6 of the Low Voltage Electrical Regulation.
2. Limitations of Use
These facilities should not be installed within bathroom ban volumes, and cold joints should not be within the protection volume or prohibition area. The heating element cannot be installed below any water distribution pipe or drain union.
3. Installation
3.1 Power Supply Circuit
The power circuit must meet the requirements of this Regulation, particularly concerning:
- Pipelines and minimum conductor sections
- Overcurrent, overvoltage, and indirect contact protection.
Control and maneuver devices should be omnipolar cut-off switches, but control devices like thermostats are allowed to be non-omnipolar.
3.2 Electrical Installation
The heating circuit is subdivided into circuits according to ITC-BT-25 criteria, depending on simultaneous use, distance, and other safety criteria, with a maximum of 25 A per phase circuit. Each circuit is protected by an omnipolar automatic cut-off switch. High-sensitivity (30 mA) differential protection is mandatory for each radiant heating cable or folio circuit. When the heating cable has armor or the thermostat has a metal casing, both must be connected to ground through a protective conductor with a cross-section equal to the phase conductor. The power cord to the thermostat (the phase) will have the same section as the cold junction and will be housed in a suitable diameter tube. Before covering the heating element, circuit continuity should be checked. After covering the cable and before placing the pavement, electrical insulation to ground should be checked and must be equal to or greater than 250,000 ohms.
3.2.1 Cold Joints
The connections of heating cables or heating panels with cold joints should be made and arranged to prevent heat transfer from exceeding the maximum permissible temperature for continuous duty as defined in UNE 20,460 -5-523. Therefore, unless there is a breakdown, cold joints should be factory-made; on-site execution is not authorized. The sections of the cold junctions are determined by the maximum permissible currents set for permanent service in ITC-BT-19. The pipe or tube shall end at least 0.20 m from the cable connection to the heater, and the union must be completely embedded within the concrete mass.
3.3 Placement of Heating Cables
When placing a heating element or cable unit on the roof or floor, it is recommended to arrange the coils parallel to the wall with the greatest heat loss. This allows for reinforcing the 0.5 m to 0.6 m strip closest to the shell and reducing the distance between turns, ensuring the maximum allowable cable temperature is not exceeded. When possible, it is recommended to minimize the heating cable length, particularly in the floor, within 0.6 m of interior walls where furniture installation is anticipated. The heating cable must be fully covered by a material with good heat conductivity, such as gypsum, concrete, or lime, to facilitate heat transfer.
3.4 Securing Heating Cables
The heating cable is fixed by non-metallic, corrosion-resistant spacers placed at points where the cable changes direction. These spacers must not damage the cable insulation. The cable’s bending radius must not be less than 6 times its outer diameter for unarmored cables and 10 times for armored cables.
3.5 Interaction with Other Installations
The heating element should be placed as far as possible from power and lighting cables to prevent heat transfer. Otherwise, the temperature of the power and lighting circuits must be calculated considering the heat emitted by the heating elements, and the appropriate section must be selected based on the cable type and UNE 20,460 -5-523.
4. Floor Heating Cable Installations
The heating cable temperature must not exceed the limits specified in UNE 21,155 -1 for insulated wires under anticipated operating conditions. The heat capacity of the material on the insulation surface and the emitting surface must be less than 120 kJ/m2K (29 kcal/m2°C).
4.1 Placement
Wires placed on the floor will be embedded in mortar or concrete. If a first concrete layer exists, it may contain insulation. The second concrete layer, without insulation, must have a minimum thickness of 30 mm and will encase the heating cables. Concrete setting cannot be accelerated using the heating element, though drying is permitted. If additional insulation is installed on the floor, a base insulator with a thickness greater than 1 cm and a height equal to the mortar or concrete layer embedding the heating element must be affixed around the perimeter. If moisture is possible, the insulation must include a moisture barrier at the bottom. If condensation is a risk, a vapor barrier should also be included. The cable outline will be at least 0.2 m from all exterior walls.
5. Ceiling Heating Cable Installations
For direct heating, it is necessary to reduce the mass of material heated by the cable construction. The thermal material between the thermal insulation surface and the emitting surface must be less than 180 kJ/m2K (43 kcal/m2°C).
5.1 Placement
The minimum height for premises using this system is 3.5 m. The heating cable outline in the ceiling will maintain a minimum distance of 0.4 m from exterior walls and 0.2 m from interior walls. Any ceiling light fixtures, including downlights, should have a clear space of at least 0.1 m around them. Ceiling-placed items will be embedded in a coating layer at least 15-20 mm thick, applied parallel to the cables. Avoid air pockets in the lining contacting the cable.
6. Control
The thermostat controlling environmental conditions should be placed on an interior wall, 1.5 m above the ground, and away from solar radiation, lamps, appliances, drafts from doors, windows, or fans. The differential thermostat must not exceed 1.5 K. If the heating element’s current intensity exceeds the thermostat’s cut-off circuit power or if the phase drops out, the thermostat will activate a contactor coil with sufficient breaking capacity located downstream of the distribution panel circuit breaker. In large venues, the project may warrant multiple thermostats to optimize energy consumption.