Creating 120/240 in a residential garage fed by just Hot/Neu 120v today

[Testerguy]

A friend wants to install a 3.3kw charger for his new Chevy Volt.  His detached garage has a single 120v/20a circuit for lighting/outlet/door-opener fed by a hot/neutral 12ga pair in 1/2" conduit (with the conduit acting as the Equipment Grounding Conductor) .  Running a new feed is expensive due to terrain/concrete stairs in the way, and the electrician on the job is somewhat reluctant to try pulling additional wires in the existing conduit (presumably due to the number of tight bends).  One solution under discussion is to convert the existing circuit to 240v. The charging system can be configured for a variety of current draws, including 12a or 16a, so the existing 12ga is sufficient.  In order to preserve the 120v for the lighting, convenience outlet and garage door opener, the plan would be to install a 240-120v transformer fed off the converted 240v circuit.<br><br>The challenge is meeting safety and code requirements for grounding and bonding, preferably without installing a separate grounding electrode and/or pulling any new wires.  Is there a safe and code-compliant way to accomplish the above by utilizing the existing conduit as the sole grounding pathway (essentially as both the GEC and the EGC) back to the primary panel, where there is a proper bonding connection between the source neutral and the home's grounding electrode?<br><br>It would seem to be safe to do so (assuming that one does a rigorous inspection of the integrity of the grounding path through the conduit, tightening all connections etc), but I have reviewed NEC section 250 (2008 and 2011) regarding SDS, Grounding, and Bonding and am having trouble determining if it is code-compliant (quick reading suggests it is not).  My question is two-fold:<br><br>1) Is there a way to do this that is code-compliant<br>2) If it is not to-the-letter-compliant does anyone know of an actual real safety issue? I do not know if the homeowner will be pulling a permit or not, but clearly wants it to be safe. If he later moves out, he could readily convert it back. I supect, though, that he will not proceed unless it is code compliant in addition to being safe.<br><br>If this is a non-flyer, what's the minimum to make it compliant (exterior grounding electrode, pull a bare grounding conductor through the conduit, etc)?<br><br>THANKS!<br>

 

[augie47]

As far as the '08 Code is concerned, IMO, a grouning electrode system would need to be established for the transformer secondary. (The conduit woould not be acceptable)

I am not familar with the '11 Code.

 

[Testerguy]

For safety as well, or just for technical compliance? i am having trouble seeing where the risk comes from in this particular case.

 

[hurk27]

To only add to Gus's post, that a transformer is isolating and the neutral/ground bond has to be re established after the transformer.

My questions is have you discussed with your friend that lowering the supply current will also lower the charge rate, and instead of just a couple hours it might take longer to fully charge the vehicle, this might not be acceptable to your friend if he always wants the car available.

Might want to discuss this with your friend, and or find an electrician who will do the job.

Also I hope he already has the car as GM shut down the plant for some reason, I can't remember why at this time.

 

[ptonsparky]

I would be for pulling out the 12s and replacing them with a pair of 8s and a 10 eg or, if you are sure of the conduit, a pair of 6s. Then use a tranny to set up your neutral.

 

[Testerguy]

To answer Hurk27's question about the charge rate for the car, the charger circuitry in the Chevy VOLT turns out to be the limiting factor in this case (max of 3.3kw/16amp). Even if he drops to 12a it will meet his particular charge-time needs.

Regarding Ptonsparky's suggestion to repull larger wire, my original suggestion was to pull new wire so that he would end up with a dedicated neutral. If he pulls two new wires he could simply add the new 240v circuit and not disturb the old. If he pulls even one more wire (opposite phase hot), he would have a couple of options that would not involve an SDS. Unfortunately, the electrician is worried that he can't succeed with the pull.

If they decide to go with the transformer, would adding a grounding electrode conductor to a dedicated grounding electrode make it code-compliant?

On a related note, what's the current consensus on using the existing metallic conduit as the EGC (no pun intended)?
Thanks

 

[hurk27]

To answer Hurk27's question about the charge rate for the car, the charger circuitry in the Chevy VOLT turns out to be the limiting factor in this case (max of 3.3kw/16amp). Even if he drops to 12a it will meet his particular charge-time needs.

Regarding Ptonsparky's suggestion to repull larger wire, my original suggestion was to pull new wire so that he would end up with a dedicated neutral. If he pulls two new wires he could simply add the new 240v circuit and not disturb the old. If he pulls even one more wire (opposite phase hot), he would have a couple of options that would not involve an SDS. Unfortunately, the electrician is worried that he can't succeed with the pull.

If they decide to go with the transformer, would adding a grounding electrode conductor to a dedicated grounding electrode make it code-compliant?

On a related note, what's the current consensus on using the existing metallic conduit as the EGC (no pun intended)?
Thanks

There is no problem with the use of the existing conduit if it has not been compromised, but you install an SDS you have to re establish an EGC and GEC on its secondaries, installing a ground rod just outside is not enough as it will be required to be bonded to the service GES but can be done out side, as I stated above.

3300 kva is about 13.75 amps, and add 25% for it being continuous is 17.2 amps, this would only leave 2.8 amps for other use, I feel if the charge rate is easily switch from one rate to another it might get switched and something get turned on and the circuit would be over loaded? but thats the choice the owner would have to make, an inspector would most likely go with the max listed rating of the charger? (not sure on that one)

Is this conduit embedded in concrete? or does it jump through to many box's? and is not a direct home run to the panel?, this would be the only two points I would say it might not be cost effective to try to remove the existing conductors and pull new, even embedded conduit if in good condition might be re-pulled? there are tools that can do it, I have re-pulled through 8 existing 90? before while not easy it is possible with allot of lube

 

[infinity]

There is no problem with the use of the existing conduit if it has not been compromised, but you install an SDS you have to re establish an EGC and GEC on its secondaries, installing a ground rod just outside is not enough as it will be required to be bonded to the service GES but can be done out side, as I stated above.

Even for a separate building?

 

[ptonsparky]

Even for a separate building?

I don't, but I have been wrong on a pretty regular basis.

 

[Rampage_Rick]

Since I've been heavily researching a Volt for myself, I thought I'd share my knowledge on the charging systems.

The Chevy Volt, Nissan Leaf, and the new plug-in Prius use a charger standard called SAE J1772. The Telsa Roadster pre-dates J1772, but it appears that Tesla is switching over. J1772 specifies 2 levels for AC charging (and 3 DC levels up to 400A, though DC units are rare) Level 1 specifies a maximum of 16A @ 120V, whereas Level 2 specifies a maximum of 80A @ 240V. The charger circuitry is generally located in the car, and the charging station is basically provides ground fault protection and tells the charger in the car the maximum allowable current.

When you buy a Volt it comes with a Level 1 charging station. It can be toggled between 8 and 12 amps. (approx 1-1.5 kW)

Level 2 charging stations are available from several manufacturers, and are generally rated 30A @ 240V. Units are available for higher currents, but generally aren't necessary as the only vehicle which presently makes use of that rate is the Telsa Roadster with an 18.6 kW onboard charger. In the case of the Volt, the onboard charger is limited to 3.3 kW. The Nissan Leaf presently had a 3.3 kW charger, but the new model year should have a 6.6 kW charger. Rumor has it the new EV Ford Focus will also be 6.6 kW.

The only Level 2 charger I'm aware of that is limited to 15 amps is the Voltec model endorsed by GM. The actual nameplate rating is 240V 15A 3600W. Granted it's designed to supply exactly what the Volt requires, but what are the odds that someone will want to plug in a newer 6.6 kW vehicle? I'm of the opinion that if you're going to the effort to install a Level 2 unit, might as well install a decent one that will handle some of the cars just coming to market.

If you're interested in a portable Level 2 charging station you could also look at one of the modified Leaf chargers available from evseupgrade.com. They take a standard Level 1 unit from Nissan (made by Panasonic) and modify it so it works as a Level 2 unit (16A @ 240V)

Voltec Level 2 wallmount (15A @ 240V) $500 *but only available with Volt VIN
EVSE upgrade portable (16A @ 240V) $1000
Schneider Level 2 wallmount (30A @ 240V) $800 @ Big Orange

But I digress... Given the scenario presented by the OP I would concur with the recommendation to remove the existing conductors and re-pull. Add another hot to the existing #12s as a bare minimum, though personally if I'm going through all that effort I'd probably want to future-proof by going with three #8s and a small subpanel in the garage. Way less headache than going the SDS route IMHO.

 

[Dennis Alwon]

I don't, but I have been wrong on a pretty regular basis.

The separate or detached structure is connected to the main gec thru the egc. There is no other requirement to run a full size gec back to the main building. Just drive 2 rods at the separate structure and do any water bonding as you would a service at the original building. The difference is the egc is bonded to the separated egc-- neutral and egc are separated-- I know you understand this info it is for the op.