Reddit reviews Cerrowire 283-3803A 25-Feet 10/3 SOOW Rubber Flexible Extra Heavy Duty Cord, Black
We found 1 Reddit comments about Cerrowire 283-3803A 25-Feet 10/3 SOOW Rubber Flexible Extra Heavy Duty Cord, Black. Here are the top ones, ranked by their Reddit score.
Rated up to 600 volts-40 to 90 degrees Celsius CPE cordFlexible strandingSunlight, oil, water, flame, ozone and abrasion resistantGreat for extra hard usage
Go get 25 feet of 10/3 SOOW cord (technical name for black rubber cord) and a NEMA 10-30P plug. It will probably be a lot that has blades you slide in to allow configurations for 10-30 and 10-50 plugs.
Others are correct. Solder is a bad idea for extending the cord. If you need 25'a new cord is in order.
Plug:
https://www.amazon.com/Hubbell-Wiring-Systems-tradeSELECT-Interchangeable/dp/B008KMTTQG
Cord:
https://www.amazon.com/gp/aw/d/B00L2O3YL0/ref=mp_s_a_1_8?ie=UTF8&qid=1469812949&sr=8-8&pi=AC_SX236_SY340_QL65&keywords=soow&dpPl=1&dpID=51jXQDjbbSL&ref=plSrch
Heavy duty strain relief: https://www.amazon.com/gp/aw/d/B00RW79KOG/ref=mp_s_a_1_28?ie=UTF8&qid=1469813053&sr=8-28&pi=AC_SX236_SY340_QL65&keywords=kellems+grip
Lighter duty strain relief:https://www.amazon.com/gp/aw/d/B005QDQZ78/ref=mp_s_a_1_6?ie=UTF8&qid=1469813373&sr=8-6&pi=AC_SX236_SY340_QL65&keywords=c750+connector&dpPl=1&dpID=51nbYwJQe6L&ref=plSrch
All this stuff should be available at your local electrical supply.