Electrical panel and adding another 220V circuit

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Old 04-28-10, 12:53 PM
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Electrical panel and adding another 220V circuit

Hello-

I'm looking at purchasing a Nissan Leaf (electric car) probably in the next 12-18 months. This car has an optional 220V charger which I will likely have installed as I'm guessing local code won't allow an unlicensed person do it. The literature I have read so far states that the charger has to be hardwired to your home, and that an electrician needs to come out and "evaluate" your home, which I assume means he/she comes down to my basement and looks at my electrical box.

I have a large 200A circuit breaker at the top of my box which I assume means I have 200A service. I also realize that the 220V circuit will require a "double" circuit breaker, and the box has plenty of room for those. The car charger can handle a 220V 15amp or 220V 30 amp circuit, I guess depending upon what can be installed in one's home. Which leads to my question.......

If I have 200amp service to my house, what determines whether I can put in a 15amp circuit or a 30amp 220V circuit (assuming I have room in my box and the proper wires are used)? Are the existing circuits currently in the box plugged into some sort of "formula" that determines what the total amperage of all the circuits in the box can add up to? Is it judgment of the electrician? Is it just making sure the box has enough space for the double breakers? I imagine that has to be some sort of rule governing the adding of circuits to a home's service, so I was curious as to what to expect when the electrician shows up.

Thanks!
 
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Old 04-28-10, 01:06 PM
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You could do a" load calculation" and you can Google that to find out more but given you have a 200 amp supply I doubt an electrician would even bother to do that. You would be better using the 30amp option because the car will charge faster.
Are the existing circuits currently in the box plugged into some sort of "formula" that determines what the total amperage of all the circuits in the box can add up to?
It is a product of the square feet of the house and any heavy demand appliances like heat and air or water heater.
 

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Old 04-28-10, 01:24 PM
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Originally Posted by ualdriver View Post
Are the existing circuits currently in the box plugged into some sort of "formula" that determines what the total amperage of all the circuits in the box can add up to?
Yes, it's called a demand load calculation which takes into account the size of the home and existing appliances. A 240V,30A circuit is not a significant load for a typical residential 200A service so I would not expect a problem. If you have an instant (on-demand) electric water heater you could be pushing the upper limit, but barring that there should be no issue.

Your charger will at most use 7.2kW of the available 48.0kW of your electrical service. This is roughly equivalent to a cloths dryer or electric oven.
 
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Old 04-28-10, 01:28 PM
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Originally Posted by ray2047 View Post
You could do a" load calculation" and you can Google that to find out more but given you have a 200 amp supply I doubt an electrician would even bother to do that. You would be better using the 30amp option because the car will charge faster. No. It is a product of the square feet of the house and any heavy demand appliances like heat and air or water heater.
OK, thanks Ray. And I do want to use the 30 amp option. I was hoping my box would have the capacity and it sounds like it does.
 
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Old 04-28-10, 01:31 PM
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Originally Posted by ibpooks View Post
Yes, it's called a demand load calculation which takes into account the size of the home and existing appliances. A 240V,30A circuit is not a significant load for a typical residential 200A service so I would not expect a problem. If you have an instant (on-demand) electric water heater you could be pushing the upper limit, but barring that there should be no issue.

Your charger will at most use 7.2kW of the available 48.0kW of your electrical service. This is roughly equivalent to a cloths dryer or electric oven.
Thanks ibpooks. I'm going to Google that demand load calculation just out of curiosity. I don't have an electric range or electric water heater or an electric dryer as they're all gas, so it sounds like I'll be OK.
 
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Old 04-28-10, 05:48 PM
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Considering that those appliances are all gas, I'd be willing to wager that your heat is also gas. You'll have no problem at all adding a 30 amp 240 volt circuit. If you calculate your load you'll probably be surprised at how low it actually is.
 
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Old 04-28-10, 06:33 PM
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Originally Posted by CasualJoe View Post
Considering that those appliances are all gas, I'd be willing to wager that your heat is also gas. You'll have no problem at all adding a 30 amp 240 volt circuit. If you calculate your load you'll probably be surprised at how low it actually is.
Your wager would be correct Now what if I got two rechargeable cars that I recharged at night at the same time while electricity was cheap........Would two 30amp, 240 volt circuits running at the same time be too much?
 
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Old 04-29-10, 12:14 AM
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With an all-gas appliance house on a 200A service, you could charge a fleet without too much hassle, easily 5 or 6. Does your utility actually bill different rate for off-peak power via a smart meter?
 
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Old 04-29-10, 06:06 PM
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Originally Posted by ibpooks View Post
With an all-gas appliance house on a 200A service, you could charge a fleet without too much hassle, easily 5 or 6. Does your utility actually bill different rate for off-peak power via a smart meter?
Yes, actually they do I think. When I actually get the car, I need to look into that as we would be charging mostly at night when I assume electricity would be the cheapest.
 
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