The heating cables are applied in different ways in stairs and entrances depending on the method of construction.
- Stairs/areas which are casted in one operation.
- Stairs/areas which are ground with a steel device after the casting.
- Stairs/areas with a coating of stone or filling.
Most often you choose a high output (300 – 400 Watt per m²), in order to obtain quick melting off and drying of the entrance. This does not mean a higher energy cost as the operating time of the cable is short.
The control of the heating cable is often done manually in combination with a thermostat. The purpose of the thermostat is to switch off the heating cable when the temperature is high enough to keep the surface dry. With bigger applications it is better to switch the heating cables on via an automatic control that can sense the moisture and temperature to decide whether the application is to be switched on or not.
When installing heating cables in stairs the cable should be applied in such a way that the output is evenly distributed amongst the treads of the stairs.
The outmost run of cable in each tread of the seal must not be applied too deep down in the step as this can cause freezing in the rubber nosing.
The sensor of the thermostat should be placed in such a way that it senses the temperature in the most exposed position of the stairs.
A suitable depth of application is 30-50mm below the surface.
Dimensioning heating cables for stairs
When calcualting the cable resistance and length this is the best way:
- The total surface of the stairs (the threads) .
- Required power (Pt).
- The total resistance (Rt).
- The shortest cable length possible (l).
- The cable resistance (Ω/m) is decided upon.
- The real length of the cable (l).
- The solution.
- Check calculation.
A flight of staris with a half-space landing of 1,8 x 1,5m
4 threads 1,8 x 0,3m, 4 risers 1,8 x 0,2m in central Sweden is to be applied with heating cables as an anti-skid device.
- Begin to calculate the total surface where the heating cable is to be applied.
Example: 2,7m² + 4 x 0.54 m² = 4,9 m²
- The required power Pt = P/m² x surface
Example: 4,9m² x 350 W/m² = 1.715 W
- Calculate the total resistance of the cable in order to obtain a power of 1.715 W when connected to 230 V.
Formula: Ohms law for power P = U² / R gives R = U² / P
Example: 230² / 1.715 = 30.84 Ohm
- The shortest length possible is obtained by dividing Pt with the max. permitted cable power. The power when applying in concrete is 25 W/m.
Example: 1.715 / 25 = 69 m
- Calculating the resistance of the cable per meter (R/m). R/m = Rt / l
Example: 30.84 / 69 = 0,45 Ohm
Theoretically calculated value is the 69m cable with 0,45 Ohm/m. We chose this value (0,45 Ohm/m).
- The length of the heating cable can now easily be worked out by dividing Rt with R/m.
Example: 30.84 / 0.45 = 69 m
- The solution: 69 m heating cable (TCPR) 0.45 Ohm/m.
- Check calculation: The total power is check calculated by ohms law for power P= U² / R
Example: 230² / (69 x 0.45) = 1.704 W.
Check: The power of the cable per meter is check calculated according to Pt / l
Example: 1.704 / 69 = 24.7 W/m
Compare these two values to the required initial values and find out whether they are within the decided tolerances.
PLEASE NOTE! When the stairs and suspended and the underneath also is exposed to the air temperature you must calculate with much higher powers (+ 50 %).