With such a thin cable, it is a rather small spindle, about 0.7 kW?
Or is it the infamous kits with “aviation connector”, where the problem is that their strain relief clamp usually will not allow cables of more than 7.8 mm wire diameter, which limits these “aviation connectors” to cables that are underdimensioned for the spindle’s current? If so, I always recommend to → consider this ← (to buy Daniel Moran’s @PwnCNC ready-to-use spindle cable here)