It really depends on physical environment particulars, and what it is you are sizing your DC currents for.
If you are talking about 4 feet, that's one thing. But if it's an RV and you are wiring up a 13.8 V DC supply circuit run from house batteries, which are where they are, to the only place in the RV you can stuff a ham shack, and it's 46.5 feet via the only possible wiring routing, then voltage drop is a big issue if you want to run a K3 plus whatever from there. It's even more interesting if what you are planning for is TWO K3's plus two laptops and whatever, and that's going to be two regular FD operating positions in a lazy and air-conditioned comfortable RV with facilities, and a cold fridge at the ready. I'll run the #4 direct from the battery terminals, and fuse it at 50 amps. That will allow the big T105 batteries to feed peak current to the shack, without having to have up-size the charger-converter (which needs to be sized to the batteries' bulk charge rate, not the load). Let the charger-converter and all that house DC wiring just worry about keeping the battery charged, just like we had gone to a site without park power, and had to do the battery plus generator afternoons thing. Gen comes on and charger-converter runs bulk charge current for a long period. They're made to do that. Also it allows us to run the air-conditioning and the house on the generator and use the T105's for class 2B on FD. Just use the regular house battery disconnect and the big batteries are all the transceivers ever see. In this kind of consideration, spending the absolute least amount of money possible is not the prime consideration, and a stiff supply voltage at the far end would justify spending money for copper. 73, Guy. On Thu, Aug 11, 2016 at 3:03 PM, Lewis Phelps <l...@n6lew.us> wrote: > I’ve changed the subject line because this discussion has strayed from the > original question. > > At retail rates (e.g. price per foot from lower.com) #6 wire is 89 cents > per foot, and #12 wire is 8.2 cents per foot; assuming Clay’s 50 foot run > and 3 wires for a 110 VAC circuit with ground, per NEC, the added cost for > wire would be $121.20. > > Is it “good engineering practice?” It seems to be to be OK from an > electrical standpoint, albeit unnecessary, and unnecessary from a cost > standpoint, albeit not harmful. > > I can certainly understand “over-specifying” wire size in a 12 volt > circuit, and using larger wire size than is required simply from > considering ampacity, because the voltage drop is a much larger change > proportionally, but I really don’t see the benefit from the expense and > added installation difficulty of using larger-than-required wire for a > 120VAC supply circuit. > > according to the online calculator at http://www.southwire.com/ > support/voltage-drop-calculator.htm, which takes into account both > resistance and reactance of the wire: > > — for a 50 foot run of cable of #6 wire, at 20 amps and 120 volts AC > single phase, the total voltage drop will be 0.884 volt, or 0.74%, for a > net voltage at the end of the circuit of 119.1 volts (rounding) > — for the same run with #12 wire, the total voltage drop will be 3.472 > volts, or 2.90 percent, for a net voltage at the end of the circuit of > 116.5 volts (rounding). > > The 3.47 volt drop would be intolerable in a 12 volt circuit providing > power directly to amateur radio equipment, but seems to me irrelevant if > feeding a competently-designed power supply that reduces the 120 volts AC > supply to some lower voltage of DC supply. Any ham radio power supply that > is specified to operate on 120 VAC should be able to operate without > difficulty from a 116.5 volts supply. > > So, why go to the extra expense of #6 wire? While it seems to me to be to > be harmless to “over-spec” the wire size, it also seems expensive and not > necessary either per requirements of Section of 310-15 of the NEC or from a > “good operating practices” perspective. > > Lew N6LEW > > > > > On Aug 11, 2016, at 11:12 AM, Kevin - K4VD <ke...@k4vd.net> wrote: > > > > The added cost of a 3x over-build seems like it would be awfully high. Is > > this good engineering practice (seriously, I don't know)? > > > > Kevin K4VD > > > > On Thu, Aug 11, 2016 at 12:38 PM, Clay Autery <caut...@montac.com > <mailto:caut...@montac.com>> wrote: > > > >> How do you define "necessary". > >> > >> Paraphrasing K9YC, Jim.... "Big wire is your friend". > >> > >> I agree... > >> > >> I typically use wire at least 2 sizes larger than "required".... Often > >> the wire size is determined by how big of a wire I can FIT in the > >> application and how much money I can part with at the time. > >> > >> For instance, on my current power project... I am running 6 AWG x 4 from > >> the service to the sub-panel @ 50 foot run for a 60 Amp separately > >> derived service where there'll never be more than about a 20 Amp total > >> demand... > >> > >> From the sub-panel to the receptacles about 3-1/2 feet below, I am using > >> 10 AWG.... only because that's the largest wire the receptacle > >> terminals are rated for. > >> > >> From the receptacles to all equipment, minimum 10 AWG... > >> > >> Bigger and shorter the wire, the better... > >> > >> ______________________ > >> Clay Autery, KY5G > >> MONTAC Enterprises > >> (318) 518-1389 > >> > >> On 8/11/2016 10:43 AM, Ronnie Hull wrote: > >>> Is 10 gauge necessary? > >>> > >>> Sent from my iPhone > >> ______________________________________________________________ > >> Elecraft mailing list > >> Home: http://mailman.qth.net/mailman/listinfo/elecraft > >> Help: http://mailman.qth.net/mmfaq.htm > >> Post: mailto:Elecraft@mailman.qth.net > >> > >> This list hosted by: http://www.qsl.net > >> Please help support this email list: http://www.qsl.net/donate.html > >> Message delivered to ke...@k4vd.net <mailto:ke...@k4vd.net> > >> > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft < > http://mailman.qth.net/mailman/listinfo/elecraft> > > Help: http://mailman.qth.net/mmfaq.htm <http://mailman.qth.net/mmfaq.htm > > > > Post: mailto:Elecraft@mailman.qth.net <mailto:Elecraft@mailman.qth.net> > > > > This list hosted by: http://www.qsl.net <http://www.qsl.net/> > > Please help support this email list: http://www.qsl.net/donate.html < > http://www.qsl.net/donate.html> > > Message delivered to l...@n6lew.us <mailto:l...@n6lew.us> > Lew Phelps N6LEW > Pasadena, CA DM04wd > Elecraft K3-10 / KXV144 / XV432 > Yaesu FT-7800 > l...@n6lew.us > www.n6lew.us > > Generalized Law of Entropy: Sooner or later, everything that has been put > together will fall apart. > > > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to k2av....@gmail.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
