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Temperature of Heating Cable?

David_CapleDavid_Caple HeathfieldPosts: 3

Hi, first post and although an 'interested gardener' (I like to experiment with such as growing from the fruit and veg you buy!) I am asking for help on a not direct gardening issue but the operation of heating cable ...

Has anyone ever measured the actual operating temperature of the heating cable they use?

I don’t mean the temperature of the soil because that will depend on such as the concentration of the cable layout, the ambient temperature of the location, the volume of sand/soil the cable is heating etc. ... I mean the temperature of the cable itself.  I’m thinking it may provide me with a warming solution I am looking for for a project.  😊  All contributions gratefully received.  Thanks for reading.

Never doubt the courage of the French ... they discovered snails are edible!  :)


  • Pete.8Pete.8 Billericay, EssexPosts: 6,527
    I don't think you'll easily find what you want to know.
    The temperature that the cable will reach is dependant on many factors.
    Ambient temperature, resistance of the cable, how quickly the heat is transferred from the cable to whatever it's heating, and I'm sure there are other factors involved too.
    If the cable is dangling in the air it will reach a different temperature to what it would reach if it were immersed in water

    If you can give us some idea of your project, maybe we can come up with some suggestions.
    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • David_CapleDavid_Caple HeathfieldPosts: 3
    Thanks Pete, I tried to imply I appreciate all of that.  :)  As you will know the key point is that a heating cable will heat it's surroundings until the temperature of the surroundings come up to the temperature of the cable and if they don't then it will keep trying until switched off.  It can't heat higher than it's own temperature! 

    So if the loss of heat from the surroundings is restricted and the heat output from the cable is higher than the heat loss to/of the surroundings then it and the surroundings will reach the maximum temperature of the cable.

    All I'm wanting to do is to slowly/gently heat a cylinder by wrapping the cable around the outside and insulating so that (nearly) all the heat is going into the object and not lost to the outside (the opposite to a heated propagator where the heat source is inside the object which then loses heat from it's outside surfaces).

    So going back to the first paragraph if the heat generated by the cable going into the cylinder from the cable is greater than the heat lost through the insulation to the outside then theoretically the cylinder will eventually reach the same temperature as the cable.  I just need the temperature of the cable so I can then calculate the the length of cable (watts) I will require and a suitable thermostat.  :)
    Never doubt the courage of the French ... they discovered snails are edible!  :)
  • Pete.8Pete.8 Billericay, EssexPosts: 6,527
    I understand your train of thought, but I'm still not sure you're going to get a helpful answer.
    I have an interest in thermodynamics (relating to quantum field theory...) but that's not helping me with your project.

    If you use a 1m heated cable that will probably use something like 25 watts.
    If you use a 5m heated cable that will use something like 125watts
    So the longer cable will heat whatever it is much quicker, but won't alter the final temperature.
    Either cable will heat to the same temperature, but the longer cable will do it much faster.

    What's wrong with doing it the old fashioned way?
    Buy a heating cable and thermostat and set the thermostat to the temperature you want to achieve.
    Or am I missing something?

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • David_CapleDavid_Caple HeathfieldPosts: 3
    Pete, yes a longer cable of the same type will produce more heat than a shorter one and will heat faster but for this to work I need to ensure that the maximum operating temperature of the cable if greater than the setting of the thermostat.  If not then the desired temperature will never be achieved no matter how long the cable, the voltage,  the wattage or how long it's left switched on for!  

    I've tried asking suppliers but they are scared s**tless of their product being used for a non standard procedure and claim they don't know so I thought ask people who are using it.  I have an old cable from 40 years ago I no longer use but cannot find it.  If I could I would experiment with it.  I'm wanting a cable that produces as least 40C and preferably 50C or maybe more.  For the reasons I have already given that's not to expect a propagator to run at those temperatures! 
    Never doubt the courage of the French ... they discovered snails are edible!  :)
  • steephillsteephill Posts: 1,729
    The maximum operating temperature of heating cables is usually specified by the manufacturer. Look for trace heating cables and you should find maximum temperatures of 200C. The heat capacity of the object you are heating and the standard of insulation you can achieve will be key to determining the energy you require to get your set temperature. The power rating of the cable will determine how fast you will get to the set temperature.
    The thermostat is key to getting the right temperature. Search for Inkbird temperature controllers, they work at the temperatures you are interested in.
  • BobTheGardenerBobTheGardener Leicestershire, UKPosts: 10,409
    I can tell you that the cable will get very hot and may in fact damage itself if dangled in the air, with no other medium to conduct the heat away.  I did that for a few seconds to warm the cable to make it more flexible before I laid it in my home-made heated bed (there's a thread about that on here somewhere.)  I was alarmed at how quickly and how hot it became, so will underline comments above relating to the use of a thermostat and would suggest you should also strongly consider using a thermal fuse in direct contact with the cable itself, to be safe.
    A trowel in the hand is worth a thousand lost under a bush.
  • Pete.8Pete.8 Billericay, EssexPosts: 6,527
    I can only say that the 2m cable I had in a propagator I had a few years ago probably reached around 40c. It felt - quite warm
    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
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