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220V vs. 240V

Fri Jun 18, 2010 8:35 pm

Can one of you engineer or electrician types explain to me why all the current (no pun intended) references to the charger are for 240 V? Until recently I always heard that home circuits and sockets were 110V and 220V. Now all I hear on the EV boards are about 120 / 240. Are these really the same thing - i.e. 110=120 and 220=240? Why the different terminology? I have a 220V home dryer plug in my garage, but is this too wimpy to support the charging station? I am concerned that the electrician will charge me to run an entirely new circuit from my panel to the garage, which are at opposite ends of the house.
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DeaneG
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Re: 220V vs. 240V

Fri Jun 18, 2010 8:46 pm

Line voltage in the US was generally 220v or 230v with a center tap for 110v or 115v up until some time (2-3 decades?) ago. It was increased to a standard 240v/120v +-5% in north America. I can't tell you why, maybe someone else knows.

Many people still refer to line voltage as 110 or 220 out of colloquial habit. But it's usually actually 240 or 120v. US appliances are designed to operate at 120v +-10% (108-132v) or 240v +- 10% (208-264v).

A "220v" dryer plug is most likely operating at 240v nominal. It is probably energized by a 30 amp circuit breaker. The current vague information is that the 2011 Leaf can only draw 3.3Kw from the 240v outlet, which is less than 15 amps. Later Leafs are rumored to be able to accept up to 6.6kW (almost 30 amps at 240v). But electrical codes limit steady current draw from a circuit breaker to 80% or less of the breaker's rating, 12A for a 15A breaker, or 24A for a 30A breaker.

We don't know yet if the Leaf's EVSE (wall unit) can be programmed to limit 240v draw to say 15A or 20A. If it can't, then you'd want to have a 30-amp capable circuit installed to operate it (40 amp breaker). If the EVSE can be set to 15A or 20A, your dryer outlet can probably be repurposed (hard wired) as your EVSE supply.

EDIT: fixed incorrect breaker current fraction
Last edited by DeaneG on Sat Jun 19, 2010 8:31 am, edited 1 time in total.
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Re: 220V vs. 240V

Fri Jun 18, 2010 9:08 pm

"220....221, whatever it takes" :lol:

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Re: 220V vs. 240V

Fri Jun 18, 2010 9:32 pm

Minor details:
I have read that 80% is the "permitted" continuous load on a breaker, so 24 amps from a 30-amp breaker.

Also, I believe that the power "standard voltage" is 120v (or 240v) +0% -10% rather than +-5%.

But, if you measure the "110" with a voltmeter in a relatively new neighborhood, you will probably find just over 119v in the (lightly loaded) morning, and rarely below 113 or 114 volts in the afternoon. But at the long end of a heavily-loaded supply wire or cord, it can easily drop to 110 volts.
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Re: 220V vs. 240V

Fri Jun 18, 2010 11:00 pm

I can't seem to find the source right now, but I remember reading that Nissan (or maybe some code) is going to insist the 240V EVSE must be installed on a dedicated 40A circuit, so your existing dryer line would not be acceptable, even though it can carry enough current for the 3.3kWh charger the first Volts will have.

And I'm sure most people know this, but you also can't just replace the 30A circuit breaker with a 40A breaker. You need to have thicker wires out to the garage.
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Re: 220V vs. 240V

Sat Jun 19, 2010 6:32 am

Here is a little history...

http://wiki.answers.com/Q/Why_was_120V_ ... er_voltage

In the United States, the electricity utility powerlines going to residential streets and roads are operated from 2300 to 2400 volts. With a 2400 volt supply, it is very convenient and easy to design and build pole transformers that have a 10-to-1 step-down ratio, thus providing 240 volts to the houses. The transformers also have a center tap to provide 120 volts from each 240-volt leg to the center point. This center point tap also provides a convenient point for a grounding connection. The actual measured voltage in your house receptacle circuits will normally be 120 to 125 volts. All appliances are rated for the minimum operating voltage (110-115), thus there is much confusion about the actual level of the supply voltages."
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Re: 220V vs. 240V

Sat Jun 19, 2010 8:17 am

Good summary explanation by DeaneG, except for the 75%. As garygid points out, it is 80%.

Confusion arises partly due to the 80%, which, unless it is specifically referenced, causes trouble especially for the 30A number, because the breakers are rated in 10A increments (except for the lowly 15A single pole). So, the 30A breaker should be used to supply 24A, not 30A. In order to make use of the 30A continuous current you DO need a 40A breaker, but the actual allowable current is 80% of 40 = 32A. I have even seen erroneous references to the 30A draw in connection with some J1772 equipment. But the J1772 does not have a pilot signal for 30A ... the signal is 32A (as it should be, and in which case, gues what, it should sit on a 40A breaker).

(More confusion: many receptacles and plug have a maximum rating of 250V printed on them.)

My house is "overvolted" ... we share a transformer with only one other neighbor. Even under load my "240V" (nominal) supply runs 242V in the mornings and 247V in the afternoons. I have seen as high as 249V, but rarely. I have seen open-circuit voltages (volt meter, no load) on the "120V" (nominal) as low as 115, but usually running 119-122V.

edit: Note: I am getting all sorts of conflicting info in researching about the 30A versus 32A pilot signal in the J1772 spec. (Also see my reply a few posts down.)
Last edited by LEAFer on Sat Jun 19, 2010 9:17 am, edited 1 time in total.
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Re: 220V vs. 240V

Sat Jun 19, 2010 8:31 am

Gary, thanks for the correction... edited my post above to improve truthiness.
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DeaneG
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Re: 220V vs. 240V

Sat Jun 19, 2010 8:42 am

The OP is actually a very good question. Maybe it's a good time to start a sticky FAQ thread, since some of our assumed info is becoming fact?
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Re: 220V vs. 240V

Sat Jun 19, 2010 9:02 am

Maybe AndyH can check a recent copy of the J1772 standard and see if the "max current" (duty cycle of a square wave) signal has discrete allowed values, or is a more-or-less "continuous" value.

A graph I "saw" (or maybe only imagined) of duty cycle vs max current was a continuous slope, rather than a series of "allowed" values. But, it might have been old, or only "suggestive" of the meaning of the signal.

If only 6-amp "steps" are allowed, then 12 (from a 15-amp breaker) might be allowed, but the popular 15 (or 16) amps from a 20-amp breaker would not be available.

So, I suspect that mandating only 6-amp steps would be a (another) poor choice for this standard.
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