I am having gutter helmet heaters installed, but installers do not hook up the electrics. I am
A electro/mechanical technician-retired, so it may be simple for me if I new the code. How do I do it, and what parts? I have one GFCI breaker in a sub-panel.
Please help,

Revans

First off, while I am glad you know that gutter de-icing cable needs GFI protection, you do not use a standard GFI device.

A standard GFI device is rated to trip at 4-6 milliamps of fault current, and is for personnel protection. This is too low, and will provide nuisance tripping.

A roof deicing system requires, per Code, 30 Ma GFI devices, of which only circuit breakers are available, for equipment protection.

You will probably not find these types of breakers in home centers. Just for laughs, ask a clerk. They may sell deicing cable, and the instructions will tell you about the 30 Ma GFI needed, but then try to find the right 30 Ma GFI breaker at the home center.

You will need to find an electrical supplier that handles your brand of panelboard. 30 Ma GFI breaker will cost about $130.00. If you decide that is too much and use a regular GFI breaker, be prepared for the deicing cable to be off more than it is on.

Once you have the right size breaker, then you need cable of the right size for your circuit and load, cable connectors, staples, and a weatherproof junction box and cover.