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High level background: I have inherited a very well maintained generator from my father-in-law (Troy-Bilt 5550). He had a 240v outlet in his garage in the event that he needed to use the generator and I would like to do something similar. Like many home-improvement projects this one has encountered a bit of mission creep and I would like to also be able to charge an electric vehicle from the same outlet in the garage should I ever get one (or if a future owner would find that attractive). I've had an electrician out at the house to look at the breaker panel, garage, and the path a cable would take to get between the two. The estimated charge was around $1250 (this was about a year ago). We've only had one extended power outage where a generator would've been useful, most are too short to warrant pulling it out. But, I want the convenience if it happens again.

Details: The house was built in 1979 and the breaker panel has a pair of 120/15amp breakers that are available to be ganged together for this project. One of the pair is empty and the other is to an old outlet that was installed above the drop-ceiling in the basement where the breaker panel is. I discovered this outlet when I set out to map everything that was on this panel as not every label was accurate. I was originally going to remove that outlet and pull the romex back to the breaker. Now I'm thinking it might be better to put a junction box at that point as part of the run from the breaker panel to the garage as it goes in the right direction and is already conveniently at the breaker panel at the location I'd need a cable.

Questions:

  • Can I use an L14-30R to connect to most EVs, or plugin-hybrids? Do they come with adapters?
  • Is a 30amp circuit sufficient for current and projected EV charging needs?
  • Is re-using the existing romex a bad idea (breaking standards) or a good idea (saving some $$)? It saves about 20-30' of an estimated 200' run.
  • Will re-using the existing romex in this manner be a deal breaker if trying to work with an electrician or will they want to do the entire thing themselves?

Desired outcome:

  • Ability to hook up 10HP generator to power most of the house (all small appliances and large appliances (2 refrigerators, freezer, dishwasher, washing machine) minus dryer and whole house A/C) while generator runs just outside the garage. The generator came with cables including a L14-30A interconnect.
  • Re-use existing romex cable run for the one breaker still in place.
  • Use same point for future EV charging (I know nothing about EVs), when the generator is not needed for power outages.
  • Keep the breaker panel tidy
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  • 1. You need an inlet to plug in a generator, not an outlet. 2. A pair of 15A 120V breakers does not give you a 240V 30A circuit, it gives you a 240V 15A circuit (assuming the pair of breakers is or can be handle-tied).
    – brhans
    Apr 15, 2023 at 17:30
  • Sounds like a lot wrong with your setup. First you are probably using a suicide cord, a cord/cable with two male(prongs) ends. Second you are probably not using a insolator to prevent the gen power going back to power lines and maybe hurt/kill linesmen. Having the proper size breakers and wire gauge is another problem. Most electricians can let you do the hard work and guide you, but their knowledge is priceless to keeping you safe.
    – crip659
    Apr 15, 2023 at 17:30
  • Suicide cord aside, the adaptor for my Tesla Model X connects to a NEMA 14-50R in my garage. I have it connected through 40A breakers. Maximum charge with this type of charger is 48A.
    – stevieb
    Apr 15, 2023 at 17:33
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    @brhans what's more, a pair of single breakers with a handle tie will suffice for a 3-wire no-neutral EV charge circuit, but not for a generator. A generator or "socket with neutral" needs common trip, a characteristic handle-ties do not provide - it's provided by an internal mechanism. Handle-ties can't do that because breakers "trip free" (trip if the handle is locked in the "on" position). But yes, the "no generator interlock", "suicide cord" and "do it all in 1 cable" are all no-go's, all due respect to past familial practices. Apr 15, 2023 at 19:54
  • How many square feet is the house, how big is the existing electrical service in amps, and is the garage attached or detached? Apr 16, 2023 at 2:23

1 Answer 1

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I would like to also be able to charge an electric vehicle from the same outlet in the garage should I ever get one (or if a future owner would find that attractive)

I understand the temptation, but it is not possible to use that circuit in a bi-directional manner in any safe, sane or legal way. (setting aside any discussion of whether your father did; I'm not touching that). It's a common request and we've looked at it every which way to do it; if there was a way to do it, I'd be happy to tell you. But there isn't. With one exception I'll cover later.

That said, I'd imagine front-of-mind is cost and we can keep that contained. However you some soft misconceptions about generator hookups, and we need to correct those.

A generator interlock is absolutely mandatory

This is a simple device that assures the utility-side breaker and generator's supply breaker cannot be on at once. This is critical, to avoid a scenario where the generator is feeding your house but the house is back-feeding the grid. This will re-energize neighborhood wires. Linemen are working on those wires to restore your power! Worse, transformers aren't diodes, and will backfeed 9600V etc. onto the distribution wires! It only takes 100mA (960 watts @ 9600V) to kill a lineman. The power company does not like backfeeders and will cut their service. Getting it back on is a costly bureaucratic nightmare.

How interlocks are implemented varies by panel. For most models of panel, someone (often the OEM) makes a kit that installs on the panel cover. We'd have to see your panel, particularly its make, to see for sure.

Some people imagine a "checklist procedure". Do A, B, C, etc. This does not work and is not allowed. Ask a competent military why - in a crisis people don't rise to the occasion, they collapse down to the level of their training. That's why they train so hard. In the dark, cold and wet, the moment it doesn't work as expected, the checklist is tossed out and people "try every combination". That's human nature. The interlock dead-ends one combination that wouldn't work anyway.

Must be a special anti-socket called an inlet

As you know, in normal life, things which supply power have recessed ports, and things which take power have exposed blades. Obviously we don't want live power on exposed blades, as that's asking for calamity. Since a generator provides power and a house takes power, thus, the generator cord must have the guarded ports and the house must have the pointy blades. This thing is called an "inlet" - here's one for NEMA L14-30 since you mentioned that.

enter image description here

With that inlet you use a "normal" extension cord - pointy bits on one end, sockety bits on the other end. I'm distinguishing that from "suicide cords" with pointy bits on both ends: a recipe for disaster. Being "locking type" does not make suicide cords any better.

Different circuit

Both interlock and inlet make it impractical to use the circuit in 2 directions. The only way that would be possible is for skilled folks to "permanently rewire" it to no longer be an EV circuit and now be a generator circuit forever, with interlock and inlet; and when the hurricane passes, "permanently rewire" it to be an EV circuit forever by moving it to a non-interlocked breaker and installing an outlet. And do that every storm. I call that "temporary permanent wiring" :) The problem is, it's a lot of work every time, and cable isn't that expensive so there's not a big savings.

The 2 circuits can be wired as direct burial laid in the trench alongside each other... but I do not like direct burial because there's no way to service the wires if they have a problem later. Unless you have a copper theft problem, then direct burial makes that harder (but so does aluminum wire, which is your friend in this application).

The wires you need

For the generator, you need 4 wires - 2 hot wires, neutral and ground. This cannot be avoided. Neutral and ground cannot be combined safely. The generator will need 30A wire. This is #10 copper, or #6 aluminum (#8 would suffice but it's not very available due to anxieties about small size aluminum).

Electric Vehicle charging does not need neutral so there is no need to run a neutral on that circuit. 2 hots and a ground will suffice. Most other things you might use in a garage - compressor, heater, kiln, welder - also do not need neutral. The EV can use anything from 15A to 100A wire, limited by a) how much reserve amp capacity you have in your main panel, and b) how much you're willing to spend on wire - though the larger you go, the more aluminum makes sense, and that is significantly cheaper!

People who drive more than 100 miles a day everyday don't generally consider an EV. For everyone else, 20A is plenty with the current regime of "car-sized" EVs. Technology Connections covers this nicely in their "home EV charging" video, I'll cue you up midway, feel free to rewind. With a few provisos. First, you might be able to get favorable "time of day" rates with the power company, necessitating doing your charging in e.g. an 8 hour period (or 15 hour period on one California plan.)

Second, right now EVs tend to be small because of battery cost, but battery prices are in free-fall. Ever wonder what happened to full-size cars like Chevy Caprice, and the station wagon that "seats about twenty"? We switched to SUVs because automakers forced us to, because government treats SUVs as "trucks" re: smog and MPG requirements. Those factors disappear with EVs, so the full size car may return. All that to say, a 30-50A charging circuit may be justified if the house can support it.

Saving money on cable

If conduit can be run, then individual wires can be run in the conduit. Better, you can forget about the EV circuit for now - conduit must be installed empty and the wires pulled in after the conduit is complete, so additional EV circuit wires could be pulled in when you're ready to pull the trigger on that. (and then you'll know the wire size). In such a conduit arrangement, ground can be shared - a #10 ground can serve a 15-60A generator, circuit or feeder.

If you aren't in a few cities that unreasonably outlaw it, you can use #6 aluminum. This is large enough that the ooga-booga scare stories about aluminum don't really apply, and most sockets and inlets will accept aluminum at 75 degree thermal. That means #6 aluminum is good for 50A.

Now if the garage is detached and you have power to it already, you're only allowed to have 1 supply circuit to a garage. (the generator circuit does not count here). As such, you will need to install a subpanel to power the 2 or more branch circuits in the garage. (e.g. lights, outlets, and the EV outlet). The generator cabling will not be involved with this subpanel at all, and will pass right by it without connecting. I know that sounds like "spending money", but aluminum works extremely well as subpanel feeder, since the terminal lugs inside subpanels are rated for aluminum (heck they're made of aluminum). So now the long haul is cheap and large. 2-2-2-4 aluminum is a common subpanel feeder, and it's 90 amps and not much more than 10/3 copper. You don't need to have the reserve ampacity in your main panel for the subpanel size, since the subpanel doesn't count - the loads in the subpanel count.

To your questions

Can I use an L14-30R to connect to most EVs, or plugin-hybrids? Do they come with adapters?

Depends how you're wiring the EV connection. That "charging thing" is not a charger, and is called an EVSE. The EVSE is a "smart GFCI" that sends a signal telling the car the safe amps it can draw. That's it! Other than that, it's empty space.

Anyway, we've established that the generator and EVSE can't use the same socket. A wall-unit EVSE is best hardwired - that sidesteps the requirement for a "dumb GFCI" on the circuit feeding the socket. A plug-in EVSE is made with a variety of plugs, and importantly, a microchip molded into the plug tells the car the safe amps. So you can make adapters, but must stay at the same amps if you do, so the microchip says the right thing.

enter image description here

Is a 30amp circuit sufficient for current and projected EV charging needs?

As covered above, it's plennnnnty unless your vehicle is mine-resistant/ambush-protected, or you need to charge within a limited window of time due to favorable time-of-use energy rates.

Is re-using the existing romex a bad idea (breaking standards) or a good idea (saving some $$)? It saves about 20-30' of an estimated 200' run.

Not worth it. You won't save enough money to bother.

The existing Romex is 14/2 w/ground. It would suffice for a 2.9 kW EV circuit (the one at the top of Alec's chart here, marked "ignore this, I didn't say it"). Most people can make that work, actually, so, okay for that I suppose.

However the generator circuit absolutely needs a complete home-run of 4-wire: either 10/3 w/gnd or 6-6-6-6 aluminum. No way around it.

Will re-using the existing romex in this manner be a deal breaker if trying to work with an electrician or will they want to do the entire thing themselves?

That makes you look extremely cheap. Electricians are swimming in well-paying work, and you're not even going to give such a cheap person a call-back, because they assume they will be a "hell customer" taking a disproportionate amount of their time.

In fact many electricians will fight you on a 20A EV circuit. They'll insist you need a 50A circuit (they may even point to the equipment nameplate on the EVSE which says "up to 50A" and incorrectly infer a 50A circuit is therefore required)... and to support that, they'll tell you your house needs a service upgrade. Electricians are making a lot of money off EVs, that's part of why they're so busy lol.

Anyway, the bulk of the cost of an installation is establishing the route for the cable, especially if it's detached and undergrounding is required. You can DIY empty conduit if you skill up.

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