Installing heating cable into raised bed

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Today I installed a heating cable into the raised bed in the greenhouse, I intend growing salad veg in the bed till the tomatoes are ready for planting, not sure if it will work the way I hope but definitely won't if I don't try.
A point of interest for anyone using heating cables, unless you are using sand as the covering material please ensure that every other organic material is kept moist, there is enough heat from these cables to ignite dry peat, so it may be the same for other flammable materials, so try and avoid testing that theory