The completed infrared heating installation must be tested and commissioned before it is put into service. This confirms that the installed heating-film load agrees with the system design and that the circuit, controls and protective devices are correctly specified.
All electrical testing, final connections and certification must be completed by a qualified electrician in accordance with the current edition of BS 7671 and the applicable manufacturer’s instructions.
1. Calculate the planned heating-film output
Where the heating-film rating is stated in watts per linear metre, calculate the planned output using:
P (W) = L (m) × Pf (W/m)
Where:
- P = planned total output of the installed heating film, in watts
- L = total installed film length, in metres
- Pf = rated output of the selected heating film, in watts per metre
If the product is specified in watts per square metre, use the installed heated area:
P (W) = A (m²) × Pf (W/m²)
The electrician must confirm that the calculated design current does not exceed the rated capacity of the thermostat, switching device, circuit conductors or protective device.
Where necessary, divide the installation into suitable heating zones or control the load using a correctly rated contactor.
2. Example: 12 metres of iH405 heating film
Two four-metre strips and two two-metre strips provide a total installed length of 12 metres.
The iH405 heating film is rated at 110 W/m:
P = 12 m × 110 W/m = 1,320 W
Using a ±10% output tolerance, the acceptable calculated range is:
- Lower limit: 1,188 W
- Upper limit: 1,452 W
3. Check the output using the measured resistance
With the circuit safely isolated, measure the total resistance of the connected heating film using suitable test equipment. Record the measured supply voltage separately.
Calculate the equivalent output using:
P = U² ÷ R
Where:
- P = calculated output, in watts
- U = measured supply voltage, in volts
- R = measured resistance, in ohms
For example, if the measured resistance is 41.5 Ω and the supply voltage used for the calculation is 240 V:
P = 240² ÷ 41.5 = 1,388 W
The calculated output of 1,388 W is within the acceptable range of 1,188–1,452 W. The result is therefore satisfactory.
4. Heating-film resistance reference
The approximate resistance for a one-metre length of heating film at the stated rated output is:
Heating filmWidthRated outputApproximate resistance for 1 miH403300 mm66 W/m872 ΩiH405500 mm110 W/m523 ΩiH4101,000 mm220 W/m261 Ω
For multiple film lengths connected in parallel, the total resistance decreases as the installed length increases.
Use the following formula:
R nominal = R 1m ÷ total installed length (m)
For 12 metres of iH405 heating film:
R nominal = 523 Ω ÷ 12 = 43.6 Ω
Using a simple ±10% resistance tolerance gives an indicative acceptable range of approximately:
- Lower limit: 39.2 Ω
- Upper limit: 47.9 Ω
A measured resistance of 41.5 Ω is within this range and is therefore satisfactory.
Important safety information
Resistance must only be measured on an isolated and de-energised circuit.
The commissioning record should include:
- Heating-film model and rated output
- Total installed film length
- Planned total output
- Calculated design current
- Measured supply voltage
- Measured resistance
- Insulation-resistance test results
- Thermostat and control-operation checks
- Circuit and protective-device details
- Final electrical certification
All final electrical connections, testing and certification must be completed by a qualified electrician.
