Raspberry PiFace, need to put 14 gauge wire in 1.5mm terminal
Have a look at this table: https://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity

It lists a source for the table and clearly states that the ampacity for free air is 7 amps. Free air means the wire is literally suspended in open air and not inside a raceway or enclosure. Inside of an enclosure or raceway, the maximum is 5 amps. BUT, remember that rating is limited by the thermal ability of the insulation. If you bundle multiple conductors all carrying a lot of current their combined heat output will add up. This the temperature up and can easily exceed the temperature rating of the insulation. So two wires carrying 4 amps might be fine. Eight bundled together might melt and/or become a fire hazard.