1mm² wire load capacity
Disclaimer: Consult local electrical code, and/or utilize a licensed and experienced electrician.

Typically there are code restrictions for what kind of supply wire should be present for different installations. This is usually a function of the Amperage of the system, not the device plugged in. For instance, a 20 amp service at 120 v in the US is typically required to be wired in 12 GA solid copper (or 3.31mm2).

Since this amperage is the primary concern, I would stick to anything larger than or equal to at least the equivalent of 14ga wire. However to minimize things like dimmer of other related circuits, I would stick to 12Ga wire where possible.

Wire size conversions - http://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html