Electrical wire requirements

[TANGOMAN]

I'm in the process of building some "temporary" light hoods for 4' Actinics on my 90g. I'm just using a standard resistance type ballast. I've got materials for DIY waterproof end-caps and I'm unsure of what gauge of wire I require. I've got "Coralife" end-caps on my 60g and it's very light/flexible wire. Maybe 18 gauge or higher ? Does anyone know what the voltage is at the bulb connector on a 40W ballast ? Is it still 120V or is it dropped ? The wiring and end-caps are later going to be installed in a canopy when I get around to building one...
I really don't want to make a fire insurance claim
FYI, I bought a 10' length of vinyl eavestrough/end caps, cut two lengths and primed/painted and they look pretty damn good...that's important because there's nothing worse than hearing "you're not leaving it like that in the living room are you ?"