Here is another question I received today from user just like you!
"Looking for best benchtop variabe powersupply to cut 2lb eps foam into surfboard blanks. The 26 g nicrome in bowcutter is 5ft in length. Thank you"
Anyone people use cutters longer than 2 feet, I typically recommend stepping it up to 24 gauge NiCr wire. You'll get better tension and less sag using 24 over 26.
If you're truly going to work with 5 feet of cutting wire, you're going to need to have a power supply with a bit of a higher voltage output. Five feet of 24 gauge will need at least 30-40 volts if you want to get up to about 5 amps. Now… five amps is just a relative value. Most foam will cut at about 2.5 amps (when using 24 gauge). But at such a long wire, you're probably going to have to go with a hotter wire to make sure your cuts are nice and fast. A wire of that length will definitely lose some heat to the environment and take a while to replenish heat when consumed by cutting the substrate.
You probably won't be able to find a cheap DC power supply that can output 40v5a. But some of the AC step down transformers are really nice, they're called "Variacs"
Circuit Specialists have a few that they stock ( http://www.circuitspecialists.com/variacs ). Honestly, if you don't mind spending the 100 bucks, I'd go with the 20amp model ( http://goo.gl/9o5ho ). That thing is a BEAST. And because it can go well beyond 5 amps, you'll be able to fiddle with your cutter until you get a nice and fast cut.
But be cautious, any voltage setting above 45 volts has the ability to penetrate dry human skin. They do have an in-line fuse which will help prevent against short circuits and electrocution. But just be really careful that no one touches any of the metal components on your cutter. Also, be careful when you set the cutter down that it doesn't touch a metal bench or a puddle on the ground, or that kinda thing. I know what some people have done is spray the metal brackets/bolts with GrillPaint. Its a high temperature and nonconductive paint, available at most hardware stores. Just a thought.One other thing you might consider is using stainless steel leader wire, used in deep sea fishing. A lot of the model RC wing builders will use stainless steel wire because they can put it under higher tension. Now, I haven't tested it myself for the electrical requirements, but apparently it is similar to nichrome wire.
Check these guys out - http://www.terminaltackleco.com/prod_detail_list/144
For leader wire gauge, I think the 80-100lb test is typically used, but maybe thinner. The stuff is pretty cheap, so you can experiment too.
If you guys have any questions, get a hold of me!