Non-dedicated 15A circuit out to garage - usable?

[DaveinOlyWA]

you do not get something for nothing. the total watts remain the same. a 120V 20A circuit would be a 240V 10A circuit. It is 2400W either way.

The key word is non-dedicated. A home run can be converted to a 240V circuit not a shared circuit can not.

Er, "but" I assume"? Yes, but a converter at the garage panel could feed all the non-240 volt circuits with 120 volts. You send 240 to the garage, and then convert, say, half of it to 120. This is only worth considering for garages that can't get another line in easily.

conversion will lower the power output but thought he had like a 30 or 40 amp circuit. either way, it does sound like a great idea worth looking into. how much does this cost?

 

[GlennD]

The title says he has 15A at 120V. This is barely enough for the supplied 12A EVSE with no other loads.

It is extremely unlikely a garage would have 30A of 120V available. At that current there would be a sub panel with both 120V and 240V.

 

[LeftieBiker]

The title says he has 15A at 120V. This is barely enough for the supplied 12A EVSE with no other loads.

It is extremely unlikely a garage would have 30A of 120V available. At that current there would be a sub panel with both 120V and 240V.

Doubling the number of Hot wires doubles the amperage as well as the voltage, I believe. Someone else already pointed this out. Although if you use the ground wire as Neutral, can a 14 gauge wire handle 30 amps at 240 volts?

 

[GlennD]

Doubling the hot wires would double the current at 120V or keep the same current at 240V. Take #12 wire. You could have 2 20A 120V circuits for 4800W or 1 240V 20A circuit for 4800W.

 

[GlennD]

You are not allowed to double small wires in house wiring. It works in your J1772 cables. I do not remember the exact size but I think it is #2 or #3. Certainly it is not #14 or #12.

 

[jlatl]

I have been reading this thread and by now am pretty confused.

Start with the original post:

• • a single 120v 15A breaker feed to the garage. To me that means the feed to the garage is probably 14ga.
  • About 40' to the garage. A would assume closer to 60' to total wire distance

Can it work if there is no other draw on a 12A EVSE? Yes, if the plugs are good, connections tight, no other draw, etc. However...

For a 120' total wire length (there and back) you have a voltage drop of 3.6v for the wire alone. Not sure what code calls for but I thought it was 2% max, or 2.4v.

There has been talk about doubling the voltage. If you converted the wiring to 240v you could still do 12A and that would give you 2.88KW. You would just need a level 2 EVSE that would not draw over 12A. Unfortunately most do.

Also, converting to 240 means you would reconnect the existing wires. My guess is that it is 14-2 w/ ground, meaning that if you did have a 120 volt step down transformer you would not have a neutral that goes back to the main box. A ground wire is typically not insulated, a neutral is. And if you did get a 120v step down transformer you would have to subtract that current from what is available to the EVSE.

If it is in a conduit I would suggest re-doing the feed. Probably 8-3 w/ ground if the conduit will support that, feed with a 40A 240v breaker (2 pole), then put in a breaker box in the garage.

Sorry, I know this is not the quick and dirty answer but it is the right way to do it. It will also give you a lot more power in the garage for future use.

Added note: If you can please verify the gauge of the wire going to the garage and that the outlets are connected with the wires under screws - not just stabbed into the holes on the outlet. Also make sure the outlet is nice and tight. If you have any doubts replace it.

 

[QueenBee]

you do not get something for nothing. the total watts remain the same. a 120V 20A circuit would be a 240V 10A circuit. It is 2400W either way.

Sure it's not free as you have to buy the new breaker, this EVSE and some slight rewiring.

Not sure what math you are trying to do but if you have a 20 amp 120 volt circuit in your garage you could run your garage lights and door opener a long with a 16 amp EVSE 120 volt EVSE, although you'd be pushing that circuit. That would give you 1920 watts of charging.

With this EVSE you would rewire the 120 volt circuit to 240 volt. Now you have 16 amps at 240 volt or 3,840 watts for charging. Then this EVSE has a step down transformer that you would connect the 120 volt circuits for lights and the garage door opener. Again still pushing the circuit but a little bit less than before.

Doesn't help the OP since this was designed for a 20 amp circuit and they only have a 15 amp circuit.

There isn't anything particular special about the EVSE that couldn't be done with a seperate step down transformer.

 

[davewill]

... Doesn't help the OP since this was designed for a 20 amp circuit and they only have a 15 amp circuit.

There isn't anything particular special about the EVSE that couldn't be done with a separate step down transformer.

Granted. I only posted it because it went with the general idea of a detached garage with only one circuit, not because I thought it would work for the OP. In general, I think this should not be used unless running a proper 240v circuit is completely cost prohibitive, the existing circuit run is in good shape, and the existing electrical needs in the garage are minimal...say just one light and a couple of plugs.

 

[rmay635703]

The title says he has 15A at 120V. This is barely enough for the supplied 12A EVSE with no other loads.

Doubling the number of Hot wires doubles the amperage as well as the voltage, I believe. Someone else already pointed this out. Although if you use the ground wire as Neutral, can a 14 gauge wire handle 30 amps at 240 volts?

How long do you want to draw that current?

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Is it twinax or similar high temp stuff?

Generally 14 guage can be used continuous with any insulation to about 15 amps,
If you have a 1920's house with bare wires in the wall it goes to about 30 amps.

If it has decent temperature rated insulation and is FLAT it should go to about 20 amps, understand that is not to code and that your voltage drop will be higher than normal. You also will need to ensure strong connections to all the outlets.

If you need 30 amps you can't go wrong with 10 gauge or better.

A trick I have done in the past is to hook unrelated circuits together, if you have one that is underutilized with 14 gauge wire (like for lights) you can buddy it, just understand that the current does not divide equally so a TRUE slow blow 15 amp fuse will be needed (one that actually blows when you exceed 15amps for a period of time not one that blows around 12.5amps like most others)

Remember though what I do for cars and trailers is not to code and if anyone looks at your house especially if you light it on fire you will get unpleasant surprises.

 

[Pringles]

I actually had my EVSE stop working thismorning because it shared a circuit with a freezer. Up until now it's been cold enough that the freezer hasn't actually been doing anything but not today!

Basically my EVSE brick said READY and the charge light would come on briefly then turn off but the READY light stayed on. I'm assuming that it sensed the voltage drop but I'm not sure. Luckily for me we did run a sub panel for the car, we just hadn't ran a dedicated outlet yet.

Running new wiring for your car is really not a fun idea but if you don't have much power in your garage its a must.

 

[LeftieBiker]

You could also put the freezer on a timer, to run only when the EVSE isn't. That won't work in Summer, though.

 

[GRA]

Semi off-topic, but called a friend of mine today to congratulate/commiserate with him, whichever seemed appropriate, on him attaining the double-nickel, and to razz him for still being older than me. Turns out he and his wife are currently renting, as their house burned down about a month back. Seems a neighbor that used a motorized wheelchair kept it charging in his carport, and the circuit overheated and started a fire. Unfortunately the neighbor also stored a couple of cans of gas for the lawnmower in the carport, and the fire soon spread from the carport, which was apparently attached to both houses, to my friend's house. No injuries, fortunately.

Apparently, I can expect a friend's house to burn down about once every 35 years, as another friend was burned out just before his 21st birthday owing to a NG water heater pilot setting off fumes in an inadequately ventilated, freshly (oil-base) painted room.

 

[Pringles]

You could also put the freezer on a timer, to run only when the EVSE isn't. That won't work in Summer, though.

I just had a sub panel put in. We just hadn't wired a new 120 outlet for the car yet. I'd been procrastinating a bit, but my car not charging spurred me to actually get it done (or more accurately SUPERVISE while my brother did it)

I did ask my brother about the sketchy wiring with converting 120 wiring to 240, and he said that the wiring WILL support it BUT its not up to code to have a white wire be the second hot wire. It seems that most EVSE's need that neutral wire though...

@GRA I guess thats why you're not supposed to store gas cans right next to your house....

 

[QueenBee]

I did ask my brother about the sketchy wiring with converting 120 wiring to 240, and he said that the wiring WILL support it BUT its not up to code to have a white wire be the second hot wire. It seems that most EVSE's need that neutral wire though...

AFAIK there are no consumer 240 volt US EVSEs that need a neutral wire. There are some commercial units thst have a 120 volt receptacle which requires a nuetral.

It's completely to code to relabel a white wire as a hot using black or red tape in a 240 volt circuit as long as it is done everywhere thst the white wire is exposed.