I don't know if most know this, but the NEC (National Electrical Code) is written by the NFPA (National Fire Protection Association). That is an organization mainly driven by fire insurance underwriters. We thus have an electrical code carefully constructed and revised to reduce insurance claims, regardless of cost or complexity. Based on what I know, it's one of the most rigorous codes in the world.
Individual States and local AHJs (Authorities Having Jurisdiction) decide which version of the NEC to enforce, and sometimes add or modify it for particular local conditions and practices. Even if you live in an area without much enforcement, if you ever have a fire because you did some shortcut in violation of NEC, you can bet the insurance investigator will find it, as they spend a lot of time and effort to find ways to deny claims. On Sun, Mar 10, 2024 at 11:24 PM Bill Dube via EV <ev@lists.evdl.org> wrote: > First, breakers themselves really don't care which way the power is > flowing. I can't think of anything about a breaker that would behave > differently if the power flows in or out of the bus bars. > > VERY large breakers need power on the input side to rewind the trip > mechanism. Even then, you simply must rewind them with the manual crank > if you are in a no power situation. (You can't reset them if they aren't > rewound.) Aside from that, they also don't care which way the power flows. > > I can't recall ever seeing a bus bar overheat due to overloading. I > suspect that the bus bars can take far more than the main breaker > current. Keep in mind that temperature is the issue. The ohmic heating > and the ambient temperature must cause the bus bar to rise to the point > where the insulation will be damaged. Each breaker that you attach to > the bus bar will both draw more current (perhaps) but will also help > wick heat away from the bus bar. > > I suppose where you place the solar breaker in the panel might matter, > somewhat. It would likely be best if you placed the solar breaker on the > far end, away from the main breaker. Thus, no portion of the bus bar > would be subject to more amps than the main breaker current. (Think > about this for a moment or two.) > > Even if you were to put the solar breaker in the middle of the panel, > the bus bars are not very likely to see a load greater than the main > breaker current, because the circuits between the solar breaker and the > main are drawing current. This draw is likely to be more than the solar > breaker is supplying to the panel. Typically (but not always) it is > general practice to install the larger current breakers near the top of > the panel, near the main breaker. > > I would guess that under any normal circumstances, the odds of a bus > bar over load are vanishingly small, particularly if you don't place the > solar breaker near the very top of the panel. > > Bill D. > > On 3/11/2024 5:52 PM, Lawrence Winiarski via EV wrote: > > I'm going to chime in with a point. Probably plenty all ready know it, > but maybe some don't. > > Virtually all home solar is actually kind of technically violating some > electrical rules. The reason is thatbreakers were not intended to be used > to back feed power, but that is the easiest way, so the code peopleactually > look the other way. > > > > The problem is as follows. > > Imagine a 200 amp panel for you house. It has a big 200 amp breaker > at the top and the bus bars are designed to handle 200 amps.Further imagine > that you have a 40 amp solar. > > So imagine you have no solar (it's dark) and you turn on every appliance > and you are drawing 200 amps. (or a tiny bit less). No problem as the > main breaker (the 200amp one) doesn't flip yet. Now turn on the 40 > amps of solar and now the main breaker is only seeing 160 amps (160 from > the power company and 40 from the solar is going into your appliances. > But the important thing is the bus bars are still seeing (or potentially > seeing 200 amps). Now start charging your EV (say it's 40 amps) so > now the bus bars are seeing 240 amps and the main breaker STILL doesn't > flip (because it's now it only sees 200 amps. > > So you are technically over powering the panel bus bars more than they > are rated for. > > The proper solution is actually to put in a NEW main breaker of 160 amps > but almost nobody does that. > > > > But the reality is the code people fudge it and allow 20% but it's not > really correct. > > Anyway I'm guessing this has something to do with your adding outlets to > a solar panel not being entirely kosher. > > > > -------------- next part -------------- > > An HTML attachment was scrubbed... > > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20240311/6489e531/attachment.htm > > > > _______________________________________________ > > Address messages to ev@lists.evdl.org > > No other addresses in TO and CC fields > > HELP: http://www.evdl.org/help/ > > > > _______________________________________________ > Address messages to ev@lists.evdl.org > No other addresses in TO and CC fields > HELP: http://www.evdl.org/help/ > > -------------- next part -------------- An HTML attachment was scrubbed... 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