On Page 32 of the D&D 5e Basic rules we have the following 14th level Wizard Ability.
Starting at 14th level, you can increase the power of your simpler spells. When you cast a wizard spell of 5th level or lower that deals damage, you can deal maximum damage with that spell. The first time you do so, you suffer no adverse effect. If you use this feature again before you finish a long rest, you take 2d12 necrotic damage for each level of the spell, immediately after you cast it. Each time you use this feature again before finishing a long rest, the necrotic damage per spell level increases by 1d12. This damage ignores resistance and immunity
Since Cantrips are Zero level spells.
A cantrip’s spell level is 0.
How do cantrips work with the overchannel ability?