17.5a is a bit on it's limit and will result in voltage drop over a distance.

2mm thin wall would be sufficient but protect the wiring as there isn't much insulation to protect the copper. 2mm thin wall is usually 28 strands at 0.3mm thick and is rated at 25a.

If you want thick wall cable then go for 4mm rated at 35a, 65 strands at 0.3mm, or 3mm rated at 27a, 44 strands at 0.3mm.