I have acquired roof de-icing cables that have a created rating needing 10amps every I have two.?

Question by garbagecasey: I have purchased roof de-icing cables that have a manufactured rating needing 10amps each I have two.?
I have a outdoor GFCI outlet that is 20 amp. Is this safe or should I wire a additional outlet? I have heard that you should only use 80 % of a outlets capacity. I have also heard that these heat cables are rated @ 10 amps each, but they will not pull that much power so a single 20 amp outlet is fine to power both. Please help with any suggestions.
would this

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