Personally id like to see how wood will set on fire because of electrical malfunction. It just doesent happen, unless theres theres high voltages involved. Theres also these little things called fuses, which cut the current if it gets grounded.
Personally id recommend malfunction-current-switch (im not sure how its spelled in US) for any outside or garage outputs. They cost some 15$ but are well worth of their protection.
Just ground the metal parts, use cable instead of some cheap bellybutton wires and theres nothing to worry about.
