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How to Test Roof Heating Cables

Key Takeaways

  • It is important to carry out a visual inspection of the cables when unboxing to ensure you are not installing damaged cables that can lead to major issues. 
  • After the visual inspection, you should carry out a power-on test by plugging in the cable in, and ensuring it warms up as it should.
  • For more advanced testing, especially when checking the insulation resistance between the bus wires and the heater grounding braid, a megohmmeter (at least 500 V dc) is essential.

How to Measure for Roof Heating Cables

heating cables

Step 1 - Measure the Roof Edge

Measure the length of the eaves (the part of the roof that overhangs) where you intend to install the heating cables. This will give you a base measurement.

Step 2 - Gutters and Downspouts

If you have gutters, measure their length. Add this to your total since you’ll want the cables to lay inside the gutters to prevent ice buildup.

Measure the length of any downspouts. If you live in a region with heavy snowfall, it’s advisable to run heating cables down the downspouts to prevent ice blockages.

Step 3 - Roof Valleys

If you’re installing heating cables in valleys (the V-shaped channels where two sloping roofs meet), measure their lengths and add this to your total.

Step 4 - Roof Overhang

Determine the width of the overhang. For every foot of overhang, add an additional foot of cable for every 20-foot run of eaves. 

This accounts for the zigzag pattern typically used during installation which increases coverage.

Step 5 - Calculate for Zigzag Pattern

If you’re installing the cables in a zigzag pattern (recommended for maximum efficiency), you’ll need to account for the vertical “drop” of the zigzag. This will significantly increase the total length of the cable required.

Decide on the spacing between each zigzag drop (typically 12-18 inches). Multiply the number of drops by the desired length of each drop, then add this to your base measurement.

Step 6 - Additional Length

Add an extra 10-15% of cable length to your measurement to account for any installation nuances, such as wrapping around roof features or ensuring cables reach power sources.

Step 7 - Power Source

Consider where your power source is located. If it’s some distance from where the cable starts, you might need additional cable length or an appropriate extension cord.

Step 8 - Check Wattage

Different cables have different wattages (often 5, 10, or 12 watts per foot). Ensure you choose the right wattage for your needs. More wattage typically means more heat output.

Check your electrical circuits to make sure they can handle the load of the heating cables.

Step 9 - Final Calculation

Add up all the measurements (roof edge, gutters, downspouts, valleys, zigzag pattern, extra length) to get the total length of heating cable required.

How to Check if Heat Cable is Working

1 - Visual Inspection

  • Check the Cable: Examine the entire length of the cable for any signs of wear, damage, or breaks.
  • Check the Connections: Ensure that the cable is securely connected to its power source and that there are no exposed wires.

2 - Power-On Test

  • Turn On the Cable: Plug in or switch on the power for the heating cables. If your system has a thermostat, you might need to adjust it to activate the cable or simulate colder conditions.
  • Feel for Warmth: After a few minutes, carefully touch the cable to feel if it’s getting warm. Do not hold onto the cable for an extended period as it can get hot and might burn you.

3 - Circuit Tester or Multimeter

Step 1 - Check Insulation Resistance

If you need to test if a heat cable is working you must check the insulation resistance between the bus wires and the heater grounding braid during the installation using a 1000 V dc megohmmeter (500 V dc minimum). 

The minimum reading should be ≥30 megohms, regardless of the length of the cable.

To do this you must:

  1. Remove the outer jacket
  2. Unwind the grounding braid
  3. Remove the inner PTC core (this is what conducts the electricity from the Bus Wires.
  4. Inside you will find the 2 Bus Wires 
  5. Connect each of the Bus Wires in turn to the megohmmeter, ensuring there is no contact with the ground wire/grounding braid
  6. Set the megohmmeter to 500 V dc
  7. Use the probe from the megohmmeter to complete the circuit

Step 2 - Record the original values

Record the original values for each circuit which you will need for future checks during regularly scheduled maintenance.

Maintenance Process for Heating Cables

Step 1 - Take New Readings During Regular Maintenance Inspections

During regularly scheduled maintenance, you should take additional readings and compare them to the original value. 

If the readings fall below 30 megohms, inspect cables and insulation for signs of damage.

Step 2 - Remove Damaged Sections

If physical damage is found, the entire damaged section must be removed and a new section of heating cable installed using only approved power kits. 

Do not attempt to repair the damaged heating section.

Step 3 - Connection Issues

If during your circuit testing there is a “trip”, or “low” or “no current” problem, yet no physical damage is apparent, the corresponding section of the cable must be removed and replaced with a new section of cable. 

This is a necessary safety precaution that should not be ignored. 

Frequently Asked Questions

At what temperature does heat cable turn on?

Most modern roof heating cables will have a number of preset options for their startup temperature. For example, Warmzone Heat Trace Cables have the following:

Startup Temperatures
50°F (+10°C)
32°F (0°C
14°F (-10°C)
0°F (-18°C)
-20°F (-29°C)
-40°F (-40°C)

How long do roof heating cables last?

Constant wattage heat cables will typically last between 3-5 years

Self-regulating heat cables are usually more durable and robust. Having a life expectancy of up to 10 years is not uncommon for these cables.

Cables Tested, Ice Melted

Roof heating cables play a pivotal role in safeguarding homes from the perils of winter. They play a pivotal role in safeguarding homes from the perils of winter.

Once installed, regular maintenance, guided by systematic tests, ensures their longevity and functionality.

If you are looking to add snow and ice melting capabilities to the roof of your home, office, or other property, take a look at the best in roof snow melting and deicing cables

Whether you own a large home or seek energy efficiency, there’s an option tailored just for you. Remember, it’s not just about the upfront cost, but the long-term benefits that a heated driveway promises.

We offer easy and convenient ways to melt away the snow every winter. Start your journey to a heated driveway system today with a free, no-obligation quote.