Does anyone have a way of figuring what wire size is when the spool or the wire is not marked. I recieved several spools of wire from my dad and the wire is not marked and he does not remember what the sizes where. The wire looks to be bigger in diamiter than the Kato power leads.
Use whatever tool you have available that can accurately measure the diameter of the bare wire and then consult a conversion table.
Maybe a cheap caliper tool would help. They can be had for a few dollars at tools outlets. However, if you have wire that is about 1/32" thick, that would be fine for feeders up to the rails here and there along your track system, provided they don't exceed about 18" in length and will never have to conduct more than a couple of amps for any great length of time. Once you get into a continuous 5-8 amp throughput, you would want 16 gauge and on down to about 12 gague, whatever you have on hand that is in good condition. It isn't the voltage so much as the heat produced in the wire due to amperage that should worry you. If the wire gets so hot that it makes its insulation burned and brittle, and that insulation flakes away, you could have wires touch each other and create a hot short. However, the voltage IS important because you don't want severe voltage losses by making the power run though tiny wires that act like resistors. As your intended voltage to the rails drops, so will your locomotive's ability to work for you. So, don't scrimp on wire, particularly the quality and the gauge. If you think you might need a bus to run under your layout, off of which will come the feeders, you shouldn't use much higher than 12-14 gauge, again depending on the requirements you have in mind. 12 gauge is household socket wiring typically, and is good for 18 amp continuous.
If you can measure the diameter of the wire (not including the insulation), you can use this table to find the gauge: http://www.powerwerx.com/wiregauge.asp You might be able to find a tool like this at an electrical supply store or hardware store: http://www.amazon.com/Stainless-Steel-Wire-Gauge-Measures/dp/B005XPSZYU/ref=pd_cp_hi_1 - Jeff
Oldscout, a cheap wire stripper will show you the approximate size of wire. I have a tool for crimping connectors that includes three strippers in the handle, 14-16, 18-20, and 22-24 AWG. You should find one at a hardware store, possibly Home Depot or Lowe's. Mine is the second on the left in the photo. It may be cheap, but it has served me well for many years. http://www.pbase.com/mainecruising/wire_termination