Separated from: http://www.doityourself.com/forum/el...my-garage.html

I was really excited to find this thread, actually, as I have a similar issue. I'm wondering if I can change a 120V service to 240V service ONLY, skipping the 120V service, which will allow me to use existing wiring.

I rent an apartment in Rhode Island, and I'm hoping to wire the detached garage for an electric car. The garage is currently wired with 10 gauge wire (single 10/2 wire) on a 15 amp breaker through 3/4" conduit, 120V service (hot, neutral, ground), but the only electric devices out there are are 2 exterior lights, which I believe I could change to 240V lights. There are no plugs, and I have no need for additional plugs. It's about 125 feet from the main panel, which is only 100 amp service, to the garage. There is no breaker box at the garage currently that I can see. This is a very old house, though the garage wiring appears a lot newer.

Now before anyone gets the impression that this is a ludicrous load for small wires, electric cars can be charged off of pretty much any power supply. At a minimum (though this will be annoying at times), I can survive on 15 amp 120V service as I can also charge at work and my commute is only 2 miles, and I'll do this if I can't come up with a solution. I don't own the home and will only be here for 2-3 years, most likely, so I'm not looking to spend a lot of money on this. Sure, ideally I would swap the 10/2 wire for 3x 6 gauge conductors with an 8G ground in the conduit (should fit) to run more amps, and install a breaker box, and maybe upgrade the main, and I'll ask about a price for this, but here's what I'm trying to do. I will be hiring an electrician, but I want to know if I'm crazy in asking this.

The device used to charge the vehicle is 240V and hard-wires into the electrical without a plug, and can be set permanently to pretty much any max amperage desired, requiring breakers of the same amps. It will actually draw only 80% of this rated load as it is a continuous load. This becomes the only load on the circuit, other than the couple LED lights outside the garage. I'm thinking 15 or 20 amps, depending on what is safe over 10 gauge wire for this distance, and I'd likely be limited by the 100amp service too. Can I have them plug the neutral of the existing wire into a second breaker on the other leg at the main, relabel the neutral a hot, take out the 120V lights and install 240V lights, and plug in my electric car charger using the 2 hots? I would not use a neutral in any of this. This would save a ton of money, seems safe to me, but I have no idea if it can be code compliant.

My biggest concerns:
1) Do I still need a breaker box and a grounding rod at the garage (the system may already use the metal conduit for grounding, I'm not sure), or can I be grandfathered in with current wiring? Currently I don't see any disconnect or breaker box. Installing a disconnect would be easy. I don't know if I need 4 wires for a 240V panel though.
2) Is it legal to convert to 240V only without any neutral and no capacity for 120V loads? This is my strong preference if it can be done.
3) Will electricians just think I'm nuts, even if it can be done safely and in a code compliant way?

Thanks in advance for any advice!
Jon

 

Then for reasons of liability you should not do any electrical work and since you aren't the homeowner even if home
homeowner permits are allowed you can't pull a permit. You can hire a licensed electrician with permission of the owner.

You only need #10 ground.Yes. You can only have one feed to the garage. The existing feed must be abandoned. You are confusing apples with oranges. The conduit is your EGC to provide a low resistance path to trip the breaker in case of a hot grounding to metal. The GEC is for minimizing atmospheric charges. Code wise yes but not practical because the existing 120 feed must be abandoned. You would have no 120v at the garage for lights and receptacles.Done in a safe code compliant way isn't crazy.If it is EMT it is already probably half rusted away and unusable.

 

Sorry, but it is against code to have an electrified detached garage without a 120V GFCI-protected receptacle, so you cannot convert the building to 240V-only. Code does not require a detached garage to have power, but if it does, switched interior and exterior lights at the human doors and at least one 120V general-purpose receptacle are required.

Also agree that whatever is done needs to be done by a licensed electrician or possibly the homeowner if they are legally allowed to work on rentals in your state.

Assuming the existing conduit is serviceable, the best option is likely to install a 50A or 60A subpanel in the garage.

 

Thanks for your replies all. Just to be clear, I'm planning to do this by hiring an electrician and with landlord permission. It seems that even though the garage doesn't seem to have a grounding rod currently (I could be wrong about having no grounding rod, I just couldn't find it), and also no receptacle or panel currently, that if I upgrade anything I might be required to put these in rather than being grandfathered in under whatever code was used originally. There are no doors, it's 4 cement bunkers each the size of a car with just a garage door per car, no way between the cars, and no other ways in. If I have a panel installed, looks like I'm going to need a 4th wire for neutral (even though I don't need a neutral for the car), so that means replacing everything by pulling new wires through the existing conduit (hopefully).

I get that 240V service with no neutral means no 120V receptacles, no 120V lights and no 120V loads. I was hoping to find 240V lights, could install a 240V outlet if this could satisfy the requirement, and I have no use for anything at the garage other than charging the car and the required lights. Looks like this may not be possible if a 120V outlet is required.

I may just put in a 120V outlet, as this is starting to look expensive and not doable, though I'll still make sure the electrician can't see a way to do 240V service alone over existing wires. I get the recommendation for 50A service to the garage and would do that if this were my house and I would be living here for 10 years, but this would likely require upgrading the main, running new wire, and likely add $2k to $4k to the cost of the job. I don't want to pay that just to charge my car faster for 2 years. Hopefully I can just install a regular 120V 15-20A plug without all this work and get by for a bit.

Thank you all!
Jon

 

A grounding rod is only required if there is a subpanel.

Does the driveway run beside the house? Maybe just park the car in the driveway to charge. Running a 240v receptacle in the house might be cheaper.

 

I'll pose a potentially cheaper option which would be to increase the breaker on the #10 cable to 30A, and at the garage install either a fused disconnect or 2 space panel such that one 15A and one 20A 120V circuit is created from the 30A 120V feed. Use the 20A for charging your car and use the 15A for powering the required lights and receptacle. Assuming it will pass local code this option will be cheaper than a full subpanel feeder, although you'll get only about a 30% increase in power available for charging.

 

Thanks for the ongoing ideas. Unfortunately, the garage is off a back alley, a common Rhode Island arrangement in more urban areas, so there's no driveway to use. As far as ibpooks's recommendation, I'll see what the electrician calculates is safe, but I'm not quite sure just how many amps I can put over 10 gauge wire for 125 feet. It's a pretty long run. I'll basically ask him to put in the maximum breaker/plug combination possible for the wire size.

Thanks to you both.
Jon