jjeff
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Leaf Number: 422121
Location: MSP MN

Re: Dryer outlet and 240 charger

Sat May 12, 2018 7:54 am

smkettner wrote:
jjeff wrote:Note because mine came with a L6-30 plug they restricted my top charging current to 30a
With a 30 amp circuit the EVSE should be limited to 80% or 24 amps.

True but with an outlet adapter to say a 14-50 outlet I'm just fine up to 30a or the rated capacity for the plug and wiring :)
It's the breaker itself that needs to be derated to 80% for continuous use, wiring and plug are fine at 100% capacity continuous. Note in Europe apparently they don't monkey around with the 80% thing, if their breaker is 16a it's 16a continuous but note they do have odd values, where we generally go in increments of 5 or 10a.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a

MikeD
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Leaf Number: 592

Re: Dryer outlet and 240 charger

Sat May 12, 2018 10:39 am

jjeff: It is my understanding (anyone please correct me if I'm mistaken) that EVSE's are designed such that the load carrying (stranded) copper wires in its charging cord are as thin as allowed (to improve its safety as thinner copper wires tolerate frequent flexing better, to reduce cost, reduce weight, etc) but as a result must use high temperature tolerant insulation (typically 105 C?). This means that at maximum rated load the EVSE cord runs hot (close to the insulation rating) and so the circuit wires connected to it must function not only as the current conductor but also as a "heat sink", i.e. they must be of thick enough gauge so that their (equilibrium?) running temperature does not exceed the rating of their insulation AND this temperature does not exceed the rating of the breaker that they are connected to (typically 75 C). Hence the special 80% rule for EVSE circuits.

Does this understanding help clarify things?

GerryAZ
Gold Member
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Location: Phoenix, AZ

Re: Dryer outlet and 240 charger

Sat May 12, 2018 11:35 am

Check the breaker and wire size carefully. NEMA 6-50 receptacles are often used for welders that are intermittent loads so the wire may not be sized for a continuous 40-ampere load (80 percent of 50 amperes). Have a qualified person check the entire circuit to verify that everything is in good condition and that the breaker matches the wire rating. If the circuit is suitable for 30 amperes, the LCS-30P Clipper Creek would be an excellent choice. If the circuit is suitable for 40 amperes, the HCS-40P would be appropriate. The HCS-50P is suitable for a 50-ampere circuit and will deliver 40 amperes if a car can accept that much. You need to specify the 6-50 plug option when you order any of the Clipper Creek models noted. Clipper Creek model numbers correspond to the circuit breaker size so the maximum output is 80 percent of the model number in amperes (24, 32, or 40 amperes for the models noted above). By UL Listing and NEC requirements, the supply cord is only 12 inches long (including the plug) so it may be difficult to mount the EVSE in a convenient location that is close enough to reach the receptacle. The supply cord on my HCS-50P (with NEMA 14-50 plug) is a high-quality, heavy-gauge cord that is rather stiff. The branch or feeder circuit derating to 80 percent is a National Electrical Code (NEC) requirement for all continuous loads, but your local codes could be more stringent.
Gerry
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015

jjeff
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Joined: Wed Jan 13, 2016 9:10 am
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Leaf Number: 422121
Location: MSP MN

Re: Dryer outlet and 240 charger

Sat May 12, 2018 5:19 pm

MikeD wrote:jjeff: It is my understanding (anyone please correct me if I'm mistaken) that EVSE's are designed such that the load carrying (stranded) copper wires in its charging cord are as thin as allowed (to improve its safety as thinner copper wires tolerate frequent flexing better, to reduce cost, reduce weight, etc) but as a result must use high temperature tolerant insulation (typically 105 C?). This means that at maximum rated load the EVSE cord runs hot (close to the insulation rating) and so the circuit wires connected to it must function not only as the current conductor but also as a "heat sink", i.e. they must be of thick enough gauge so that their (equilibrium?) running temperature does not exceed the rating of their insulation AND this temperature does not exceed the rating of the breaker that they are connected to (typically 75 C). Hence the special 80% rule for EVSE circuits.

Does this understanding help clarify things?

I looked at a couple of my EVSEs. My OEM '12 has 105c wiring on both input and output, 12 gauge capable of 20a continuous(mine was upgraded by EVSEupgrade.com).
My '13, also upgraded by EVSEupgrade.com has 90C wiring on both input and output, 12 gauge and again capable of 20a continuous.
My 30a(continuous) GE EVSE has 10g 80c output wiring and a 60c 8g input pigtail 14-50 I installed.
I'm not really sure why the differences in C but AFAIK all 10g wiring should be able to handle 30a continuous. Of course stranded wire does vary in the diameter of the individual wires that make up the bundle, the finer the wire the more flexible it would be and the more amperage it should be able to carry for a given diameter of the bundle, the C rating is the rating of the jacket around the wire.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a

MikeD
Posts: 655
Joined: Thu Jun 24, 2010 6:14 am
Delivery Date: 12 May 2011
Leaf Number: 592

Re: Dryer outlet and 240 charger

Sat May 12, 2018 6:40 pm

jjeff: Portable EVSEs have to be designed very conservatively because the user may at times be forced to charge at an outlet whose circuit is unknown and has minimal or no utility as a heat sink, among other issues.

Your GE EVSE example is right on the borderline, it seems to me. 10 AWG wire will heat up to approximately 60C with a 30a current assuming ambient 30C (86F) according to NEC table 310.15, so there is no margin for higher ambient temperatures, which rules out using 60C 10 AWG circuit wire even without resorting to the 80% rule. This ultimately reasonably leads to requiring using 8 AWG like you appear to have done, applying the 80% rule.

wwhitney
Posts: 736
Joined: Sat Jul 17, 2010 10:10 am
Delivery Date: 01 Apr 2011
Location: Berkeley, CA

Re: Dryer outlet and 240 charger

Sat May 12, 2018 8:20 pm

MikeD wrote:10 AWG wire will heat up to approximately 60C with a 30a current assuming ambient 30C (86F) according to NEC table 310.15

That's not what Table 310.15 means. The allowable ampacity has to be a safe figure in the worst case installation scenario. So the 30C rise you mention (from 30C to 60C) would be more than the worst case expected, e.g. 3 such conductors embedded in heavy thermal insulation. The typical case would be a much lower temperature rise.

As for the 125% rule for continuous loads, it is all about the limitations of standard circuit breakers, nothing else.

Cheers, Wayne

smkettner
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Location: Orange County, CA

Re: Dryer outlet and 240 charger

Sat May 12, 2018 9:16 pm

wwhitney wrote:As for the 125% rule for continuous loads, it is all about the limitations of standard circuit breakers, nothing else.

Cheers, Wayne
Yes and the wire still needs to be rated for breaker ampacity yea? Might be for the one but they really go together.
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MikeD
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Joined: Thu Jun 24, 2010 6:14 am
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Re: Dryer outlet and 240 charger

Sat May 12, 2018 11:06 pm

wwhitney: Thanks for your input! I'm just trying to make some rational sense of all this (but realizing that for the most part these tables are probably backed by complex mathematical formulas involving multiple variables -- and perhaps experience data as well). Do you have a good available source (or two) that you would recommend that attempts to provide rational explanations, such as some NEC handbook?

When I took an NEC class 8 years ago, I believe I then wrote the following note to myself above the NEC 2008 310.15 table:
"Note: It is useful to understand that these tables tell you what temperature a wire will reach (60C,75C,or 90C) under continuous operation with the given maximum current (90C for AWG 10 at 40 amps, for example).".

Is your last comment fundamentally disagreeing with the use of this table in this way? Understand that I'm not trying to be too precise, but just seeking a working understanding for the NEC rules -- in hopes that I will be less likely to make avoidable gross errors.

And, are you saying the concept of wiring also serving as a heat sink for a hotter component in the circuit is wrong?

Perhaps it would be better to just address my previous post to jjeff that ends with "Does this understanding help clarify things?".

Thanks, again.

wwhitney
Posts: 736
Joined: Sat Jul 17, 2010 10:10 am
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Location: Berkeley, CA

Re: Dryer outlet and 240 charger

Sun May 13, 2018 7:58 am

smkettner wrote:Yes and the wire still needs to be rated for breaker ampacity yea? Might be for the one but they really go together.

Yes, of course, I didn't mean to imply otherwise.

Cheers, Wayne

wwhitney
Posts: 736
Joined: Sat Jul 17, 2010 10:10 am
Delivery Date: 01 Apr 2011
Location: Berkeley, CA

Re: Dryer outlet and 240 charger

Sun May 13, 2018 11:19 am

MikeD wrote:When I took an NEC class 8 years ago, I believe I then wrote the following note to myself above the NEC 2008 310.15 table:
"Note: It is useful to understand that these tables tell you what temperature a wire will reach (60C,75C,or 90C) under continuous operation with the given maximum current (90C for AWG 10 at 40 amps, for example).".

I'm just taking exception to your use of the word "will" above. The actual conductor temperature under operating conditions will depend on a number of other installation parameters that will affect the rate of heat loss from the conductor. So I would expect that the allowable ampacity would be a current that will keep the conductor under the associated maximum temperature for (almost?) all possible installation scenarios (for the given ambient temperature and number of current carrying conductors in close proximity).

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