You make a lot of assumptions there: 1) It is not a 50 foot run carrying 120... It's a 50 foot 4 wire run carrying 240 volts to the sub-panel from the service plus the neutral and the green wire. Then a 6-gang box containing 8 x 120 and 4 x 220 receptacles wired independently. 2) IF some day I NEED 60 Amps, I will be able to get it because I BUILT for it... No climbing back into the attic. No buying all new wire. No pulling new wire. 3) I don't pay retail. 4) There are other considerations other than cost and electrical.... there's RF radiation from and to the wire, etc. Which is why the wire is BOTH hand-twisted into pairs AND run in bonded flex-steel conduit.
IF I built for 20 amps now, and then later needed 20+ amps, I would have to REBUILD... my time is worth more than the cost differential. I want to TALK on the radio and build OTHER stuff... NOT do repeated upgrades of my power infrastructure. Bottom Line: My stuff works and doesn't break. I don't have to use my time to do stuff twice. And because I want to... :-) ______________________ Clay Autery, KY5G MONTAC Enterprises (318) 518-1389 On 8/11/2016 2:03 PM, Lewis Phelps wrote: > 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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
