On Thu, Aug 27, 2020, 22:55 EVDL Administrator via EV <ev@lists.evdl.org> wrote:
> On 27 Aug 2020 at 19:23, Offgrid Systems via EV wrote: > > > Anytime you want a 100A circuit (or larger) for your house or > > outbuilding. Pretty common actually, since every house and most > > buildings have a service entrance. > > I'm surprised to hear you claim paralleled conductors for increased > current > capacity are "pretty common" in home wirng. I think the 'pretty common' referred to whether 1/0 wire is used in homes, not whether parallel conductor wiring is used. 1/0 is is common for high amperage circuits. Parallel wiring methods are unusual. More info below. I've never seen them in home > wiring, period. Not in service feeds, not in subfeeds, not anywhere. > Not > even in homes wired by clueless unlicensed amateurs, and you never know > what > those folks will do. > > However, I've read that they're sometimes used in commercial and > industrial > buildings. > > As Mr Sharkey said, the NEC is restrictive on how they can be used in > wiring, regardless of where. > > For a hobbyist EV, though, I don't see why you can't use them as you see > fit. > Tesla uses, or at least has used, parallel conductors inside of their portable EVSE cables to keep them smaller and more flexible. Other EVSE handle/cable assemblies may also use similar parallel wire. AFAIK, this is allowed in part because it is inside an appliance rather than in permanent house wiring (like inside a wall). I don't think the NEC has jurisdiction over wiring inside appliances. Roughly speaking, NEC rules start at the utility meter and end at the wall outlet. Parallel 1/0 AL wiring can be useful at home for providing 200 amp service to additional structures. Typically a 200 amp rated run would use 4x 4/0 AL THWN-2 wire, which has an NEC ampacity rating of 205 amps. Another option is to use 7x 1/0 AL THWN-2 which will fit in a 2" PVC conduit (according to fill calculators). The ground wire may be allowed to be smaller, but for simplicity it can be identical to the rest. 1/0 AL THWN-2 wire ampacity is 135 amps per conductor. 2x 135 = 270 amps. But there is a catch: NEC rules for current carrying conductors force a derating to 80% when there are 4-6 CCCs in a single conduit. 270 x 0.8 = 216 amps after derating. Things to note with 7x 1/0 AL vs 4x 4/0 AL: 1.) 7x 1/0 AL has a higher ampacity, both before and after derating. The circular area is the same, as these 2 sizes are exactly 3 sizes apart so resistance is the same. 2x smaller wire has more exterior surface area than 1x larger wire which allows for better heat dissipation. 2.) 1/0 AL has a mechanical flexibility advantage over 4/0 AL. 4/0 is stiffer. This may make a difference in some wire pulling situations. 3.) 7x 1/0 AL has a usage flexibility advantage. It can be used as 1 big 200 amp circuit, or be split into 2 separate 100 amp circuits if needs change (say to separate solar production on a remote building from consumption at that building). 4.) 7x 1/0 AL as a single circuit offers partial redundancy as L1, L2, and N are each carried by 2 wires. Although no single 1/0 wire can carry a fully subscribed 200 amp load, each wire can carry about 2/3 of the max load. This is still enough capacity to be useful in the situation that some wires somehow end up damaged. With 4x 4/0, if you lose the L1 or L2 wire, you will only have 120v available at the far end (unless you can repurpose the ground conductor and change the remote service to a 3-wire service). 5.) Terminating parallel conductors can be tricky. Home electrical equipment usually has lugs designed for one conductor. Adding a second conductor landing point is not easy. These kind of parts aren't easy to find. Best option I know of are multiport insulated terminal lugs. Lugs with at least 3 ports like the Ilsco or Polaris IPL/IPLD can be used to convert each set of parallel conductors to a short single 4/0 for termination. These lugs can be pricey. 6.) Teeing off of parallel conductors requires connecting to both paralled conductors at the tee point. Pass-through/dual sided entry multiport lugs can be used if they have a minimum of 3 ports (2 pass-through, 1 branch). Single entry lugs will need at least 5 ports (2 in, 2 out, 1 branch). Add another port if the branch is also going to use parallel conductors. 6 port lugs can cover all the scenarios above but can be unwieldy. Pass-through/dual sided entry lugs offer a lot of wire placement flexibility. The above is based on experience. I had not seen any prior examples but I did my NEC homework. I had the 7x 1/0 method reviewed by a licensed electrician, and inspected and approved by the state electrical inspector. I'd probably do it the same way if I did it again, particularly for the mechanical and usage flexibility benefits, and inherent redundancy. -------------- next part -------------- An HTML attachment was scrubbed... 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