Wire heats up as current flows through it, AC or DC. Say the cable is 12 gage nominally rated at 20 Amps. That rating comes from the wire in insulation in a secondary insulation in open air at 25C. When it is coiled the open air part has been eliminated and the cable get hot enough to notice or cause the insulation to fail. The wire is 3 conductor because most of us want a ground for safety.
-----Original Message----- From: ev-boun...@lists.evdl.org [mailto:ev-boun...@lists.evdl.org] On Behalf Of Martin WINLOW Sent: Sunday, February 23, 2014 7:24 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] Getting Around Energy Density by Tethering - EVs For Agriculture "three conductor wire" - Do you mean 3-phase? Why do ordinary domestic AC mains cable reels heat up if used coiled, then? MW On 22 Feb 2014, at 17:26, Bill Dube wrote: > AC, not DC powered. Transformer changes ~13 kv distribution voltage down to 480 vac. > > Cord reels ("coils") consist of three conductor wire with current flowing equally in both directions, so there is no inductance associated with the "coil". Thus no inductive heating from the AC. > > On 2/22/2014 3:55 AM, Martin WINLOW wrote: >> Hi Bill, >> >> I'm assuming the power must be DC... or otherwise wouldn't the coils get V hot? Or is this what the transformer you mentioned deals with? >> >> MW >> >> >> On 21 Feb 2014, at 17:53, Bill Dube wrote: >> >>> Electric coal mining equipment is cord-connected. Even enormous draglines ("steam" shovels on steroids) are typically cord connected with 13 kV cables. It is a mature science. Coal mining equipment has been electric powered since the early 1900's. Specialized cables, reels, transformers, and equipment for the mining industry. Easily transferable technology to agriculture. >>> >>> They typically put a reel on the back of the mining machine that pays out (or pulls in) the cable as needed. They have a "load center" transformer that is moved around as the mining process proceeds. >>> >>> Electric shuttle car for underground coal transport from working face: >>> http://www.undergroundcoal.com.au/fundamentals/11_face.aspx >>> >>> Nifty tutorial on cables for mining EVs: >>> http://www.cdc.gov/niosh/mining/content/deratingfactors.html >>> >>> Dragline cable: >>> http://www.miningphoto.com/details/2140/dragline_working_in_background_remov ing_overburden_with_drill_rigs_drilling_blas >>> >>> Bill Dube' >>> (Used to work as an Electrical Inspection intern for the Mine Safety and Health Administration, MSHA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
