Electric Vehicle Charging Circuit

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  #1  
Old 06-26-13, 11:13 AM
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Electric Vehicle Charging Circuit

I'm working on installing a level 2, 240 Volt @ 16 amp charger for my electric vehicle. My local utility offers discounted rates if I install a submeter - the submeter can be fed from the main panel, and they use math to subtract the submeter's usage from the main panel's and apply the lower rate to the submeter usage. I plan to pull a permit for the work and have both the city and utility inspect my work, but for my plans I wanted to confirm if my proposal is adequate before submitting them.

I'm planning to install a 2-pole, 20 amp breaker at my main panel. From the breaker, I planned to run 8-2 (to future proof it if I get a 40 amp charger in the future) through 1/2" NM flex conduit to a 100 amp meter socket only with no breaker. On the line side of the meter socket, I would connect the two hots, as well as the ground wire from the ground bar in the main panel. On the load side of the meter socket I would run 8-2 to my level 2 charger, 2 hots and the ground, also through the 1/2" NM flex conduit.

Does anyone see any issue with this setup? Particularly I know that the meter socket is normally wired with the two hots and a neutral wire - since it is acting as a sub-meter is it OK to use the ground instead of a neutral?
 
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  #2  
Old 06-26-13, 12:15 PM
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You could run four wires, but if you don't need a neutral for the charger, why bother. How many prongs does the plug for the vehicle have?
 
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Old 06-26-13, 12:29 PM
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Watthour meters do not generally have a neutral connection.
 
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Old 06-26-13, 01:56 PM
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The charger is hard wired and has three conductors, two hots and a ground. So no neutral, which is why I was planning on just connecting the ground in the socket. My understanding is normally a meter socket is connected to the neutral center wire from the service drop so just wanted to make sure that using the ground instead is appropriate for a sub meter.
 
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Old 06-26-13, 06:22 PM
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Type NM cable cannot be run outside.

*8-2 cable in a 1/2" conduit is probably overfilled without looking at the tables.
 
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Old 06-26-13, 06:37 PM
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Do you have a manufacturer's name and catalog number on the meter socket? A typical meter socket has lugs that will not accept wire as small as a #8 and the ground wire in 8-2 NM cable is just a #10, even smaller. The meter socket box will have to be grounded.
 
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Old 06-26-13, 06:41 PM
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From the breaker, I planned to run 8-2... through 1/2" NM flex conduit... On the load side of the meter socket I would run 8-2 to...
I missed that you were thinking of pulling a cable through the conduit. Only individual conductors should be used in continuous conduit.
 
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Old 06-26-13, 06:54 PM
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The "aftermarket" wattmeter will probably be similar to an e-mon d-mon which isn't really a meter that plugs into a pan but a stand alone device.

Unless the power company offers a sub meter which I'm not aware of them doing.
 
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Old 06-26-13, 07:22 PM
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Personally, I would run the conduit and run three 12ga wires. With conduit, you can easily pull new wires if/when needed.

No issue of course with upsizing, but I wouldn't spend the money until I needed it.
 
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Old 06-27-13, 07:34 PM
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The "aftermarket" wattmeter will probably be similar to an e-mon d-mon which isn't really a meter that plugs into a pan but a stand alone device.

Unless the power company offers a sub meter which I'm not aware of them doing.
That was my initial thought too, but the OP said

I planned to run 8-2 (to future proof it if I get a 40 amp charger in the future) through 1/2" NM flex conduit to a 100 amp meter socket only with no breaker
The typical 100 amp meter socket can handle at least up to a 1/0 conductor, but I don't think it can handle a conductor as small as a #8. Unless the meter is owned, sealed and regularly read by the power company, how could they differentiate between normal useage and battery charging useage? I assume their meters are read remotely by a system such as cellnet. I can't see any power company sending a meter reader out on a special trip to read this submeter and then discounting the power used.

The OP hasn't been back since the initial post, I hope he/she comes back.
 
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Old 06-27-13, 08:24 PM
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Hey guys - this is an actual meter installed and monitored by our utility. Here in Sacramento all customers have been converted to smart meters - so how it will work is the utility provides a second meter, fed from the primary, and they subtract the usage logged by the submeter from the main meters usage, and bill the lower rate for submeter usage. No human meter readers so its really not any more work for them, its all automated. Also they provide a rebate of $600 to install one so it ends up being a pretty sweet deal.

The socket I'm looking at is a Square D UTRS101B. The spec sheet looks like the lugs will accept down to #8 wire. And yes I will be running individual stranded 8 AWG THHN wire through the 1/2" NM liquidtite, not Romex as I initially planned. I'm meeting with the utility next week and also will have to go through the building department so I'll post back if I hear of any more requirements!
 
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Old 06-28-13, 08:36 PM
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You will need either a 1/2" hub or a closing plate according to the manufacturer's specifications; the socket is supplied with a hub opening. Ask the utility whether you should terminate the ground in the neutral lug or a field installed ground lug.
 
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