Hacker News Reader

Comment by giantg2 | Hacker News Reader

Somewhere a copy of the NEC is bursting into flames.

You'd be better of installing a new circuit with proper equiptment. Most homes would be able to at least accommodate a 20amp 220v socket, which takes about 40% of the charging time of a regular socket (15amp 110).

View on HN

OTOH I see no fundamental reason that one couldn’t build an EVSE that connected to two different outlets and drew from both of them. Two branch circuits supplying the same device is not especially rare.

I've never seen that. With the right protection circuits it could work safely. However, most garages seem to only have one branch anyways, so might as well add a 20amp+ 220v branch.

In a (large, recently constructed) garage, it seems likely that you've got multiple circuits with outlets. If you've got multiple outside outlets, they're probably all on the same circuit. If the hots are the same phase, I don't know if there's a way to determine if they're behind the same breaker or not. If the hots are on different phases, you need to return to each neutral or the gcfi that's likely to be present on an outdoor outlet will trip.

>I don't know if there's a way to determine if they're behind the same breaker or not.

Turn the breaker off and plug something in and see if it turns on

Well yeah, but it'd be a bad idea to make a charger with two 120v plugs, because chances are people will plug them both into the same circuit.

I'm not defending the idea of using two out-of-phase 110V circuits, but... this theoretical EVSE could detect its two inputs not being out-of-phase, blink its red "110V only" light, and only use one of the inputs to charge at 110V instead of 220V.

I’ve seen carpet cleaners where their machine had two 120v cords that needed to be on different breakers

If either circuit had arc fault or ground fault (or both) it would trip if you tried drawing power from both. Which is going to include pretty much any plug outside or in a garage in the past 30 years.

Yes, it'd create a multi-path circuit causing the trip.

This (multi-path circuits) is not uncommon when homeowners try to wire up a smart switch requiring a neutral to a switch-circuit without a neutral (as most light switches actually only need to switch the hot) and so they "borrow" a convenient neutral from a neighboring circuit which causes it to immediately trip!

If you are going to that effort do a 220v with a 60amp, should cost almost the same but is typically the top of level 2 charging specs.

Yeah, I put 20amp because the higher amps are nice, but many panels aren't going to handle an additional 60amp circuit (and be NEC compliant). Most panels should be able to handle an additional 20amp circuit though.

Reply on news.ycombinator.com