Absolutely no battery strain if you charge at the full 11.5kW rate (240V and 48 amps.) The 11.5kW charging rate is 1/7th of 1C where C is the capacity of the battery in kWh (~80kWh). Lithium batteries are less stressed if the charging rate does not exceed 1C.
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Advice on Wall Connector install
- Thread starter SlowKnee
- Start date
It makes no difference to the battery.
I'm of the opinion this is incorrect. I believe poster is referring to this:...Romex is only....
However that rating is conservative since it takes into account the case where people will route it in a hot uninsulated 130 degree summer attic....
So sorta, 40 years ago... Today Romex is derated to 55 because the outer sheath holds heat and is not 75F rated as the internal insulation is. Not to correct for hotter environments! In fact, there is an additional calculation required for high temp/heat situations like attics, and it applies to all cable types.
Post #3 offers the NEC references for the correction factors.
Here it is:
So you think, absent high ambient temperatures, 6 gauge Romex can heat itself to 60+ Celsius drawing 60 amps? Seems unlikely, but maybe?I'm of the opinion this is incorrect. I believe poster is referring to this:
So sorta, 40 years ago... Today Romex is derated to 55 because the outer sheath holds heat and is not 75F rated as the internal insulation is. Not to correct for hotter environments! In fact, there is an additional calculation required for high temp/heat situations like attics, and it applies to all cable types.
Post #3 offers the NEC references for the correction factors.
Here it is:
View attachment 925526
I lack the training needed to have a qualified opinion. The NEC, on the other hand, does. Looking at above I see they begin de-rating 60c rated insulation above 40C ambient. 40x2x.9+32.. 104f. Lotta attics break that quite quickly…
not sure what you know about thermal transfer, but this is likely a result of decreasing delta T and resultant loss of ability for the wire to release heat.
A guess? Romex is allowed to be within insulation. I’m guessing the heat problem begins inside insulation at full load.
not sure what you know about thermal transfer, but this is likely a result of decreasing delta T and resultant loss of ability for the wire to release heat.
A guess? Romex is allowed to be within insulation. I’m guessing the heat problem begins inside insulation at full load.
I can see that to some it may read that Cosmacelf and I ended up saying the same thing. Nope. He suggested it was a hot summer attic, AKA ambient temps, and I've hopefully politely shown that's a different correction with fixed values for all cable types.
Heat retained by surrounding insulation which is my straight up WAG, is not attic ambient temps, and thus the difference. An easy example would be running down an insulated wall. No air movement, buried in insulation, but not attic ambient heat temps either.
If you extend my working assumption a bit you can see that Romex, derated for whatever reason is further derated for high attic ambient temps just as the code demands.
Cosmacelf: Certainly my best wishes. I hope our chat has not been seen as argumentative. I hoped to clarify, not offend.
Readers, keep this in mind: I'm GUESSING, as in two guys chatting back and forth (hopefully friendly like) that Romex buried in insulation is a component of why Romex gets to 55 and not 60. NEC code is fact, as is attic ambient correction. And again, I'm just not qualifed to explain the "why the NEC says". I just happened to know ambient correction is a separate thing.
My best to all!
-d
Heat retained by surrounding insulation which is my straight up WAG, is not attic ambient temps, and thus the difference. An easy example would be running down an insulated wall. No air movement, buried in insulation, but not attic ambient heat temps either.
If you extend my working assumption a bit you can see that Romex, derated for whatever reason is further derated for high attic ambient temps just as the code demands.
Cosmacelf: Certainly my best wishes. I hope our chat has not been seen as argumentative. I hoped to clarify, not offend.
Readers, keep this in mind: I'm GUESSING, as in two guys chatting back and forth (hopefully friendly like) that Romex buried in insulation is a component of why Romex gets to 55 and not 60. NEC code is fact, as is attic ambient correction. And again, I'm just not qualifed to explain the "why the NEC says". I just happened to know ambient correction is a separate thing.
My best to all!
-d
No, it's not "further" derated. That's not how the temperature deratings work. It starts from a different point. Let's look at the Romex example. 6 gauge Romex is listed with a standard 60 degree C rating for general installation. That shows 55A capability. But to start calculating for temperature derating, you don't start from that 60 degree point and keep going down from there. It starts from the temperature rating of the individual insulation on the wires, which is for 90 degrees. That 90 degrees would start counting it down lowering it from 75A to some lesser value.
So then it's a "which is the lesser thing" race to a crossover point. If you derate from the 75A value, and it's really hot, so it ends up way down at 51A, then yes, you have to use 51A. But if it goes from 75A only down to 61A, you don't get to use 61A; you have to stick with 55A, because you can't go over that.
So in other words, it's already kind of pre-accounting for it being pretty hot overall, and it's rare that the derating calculation would push it down far enough that it gets below its already default lowered value from that 60 degree column.
Mrbrock
Active Member
There’s no difference in battery strain from 40 to 48 amps. Don’t worry about it.
Sorry Rocky, got busy and didn't get back to this till now.
I sense you know this area well, so if you would decode something for me?
* Romex is, at least sometimes, THHN inside a sheave. That sheave gets derated for some reason, and while the "why" is, at least in this thread, somewhat unclear, it seems likely it's a temperature thing.
* You tell me, and I can see the argument, code allows Romex to be treated just like THHN when correcting for ambient.
Question: Do you happen to know why? Obviously I lean towards thinking it's sheath related. Either A, the sheath is only good to 60C, B, the sheath traps heats limiting the heat potential of the combination, or C, not being required in conduit less able to conduct heat away. If any of these, or any combination, were true it would seem Romex, being heat constrained, would not be as heat tolerant as THHN in conduit would be and should be de-rated more than TTHN alone.
Comments?
Yes, basically sheath related. It's kind of like two analogies with people's body heat. It's like wearing a coat versus not wearing a coat. Or you could also think of people huddling together to share warmth instead of being spread out so the heat dissipates more. The sheath does both of those, acting like an insulating blanket around it and holding them closely together.
I didn't say treated "just like" it. There is a noticeable difference. You start calculating the number from the same point. But with the wires in conduit, the resulting derating number you get is what you get to use. With the Romex, it has a lower cutoff value that you can't go above. So if you do your calculation, and the result is above what the table shows for the 60 degree value, you can't use it, because it's too high, and you have to fall back on the lower default value. The sheath warming factors put a lower cap on how high the amps are allowed to go.
I'm gonna smack the next guy who disses a DIYer saying your house is going to burn down if you don't get a licensed electrician. It's probably rare to find one who will go through the wall connector commissioning procedure, mine certainly didn't. So there we were, set for 60A on a 50A breaker and 6/2 NM.
Side note they should probably make the default 50A.
Side note they should probably make the default 50A.
Yep. All electricians should know safety critical settings for all equipment they install, but many don’t. They also do things like make mistakes in load calculations (had that happen to me, it was a spreadsheet formula error). It is your house, make sure you understand everything going into it!
I don't think there even is a standard load panel calculation that would be valid for my situation. 100A service, there is no AC and the furnace, water heater and range are all gas, but there is a hot tub and electric dryer. Also there is a significant amount of heat tape on the roof. Without doing any analysis the guy said no problem, we'll just put in a 50A circuit. I'm sure it won't be a problem right up to the point that it is. I asked him to put in a 30A breaker and told him we would set it for 30A but I don't think he knew what I was talking about. In his mind bigger is always better so I got 6/2 romex and a 50A breaker. I'm picturing people coming home and cranking up the hot tub while Mom does laundry and Dad pops the NACS plug in for a full 48A.
It's set to 30A now even though it's on a 50A breaker, doesn't seem like that should be a problem.
Using a splitvolt type transfer switch on one of those original plugs would probably pass muster.
Most of these “electricians” seem to be monkey see monkey do types and don’t understand the rules behind anything they actually do.
The dryer is the obvious lynchpin here. We rent this place out. I think we should be ok with the wall connector pulling 24A but thought about putting up a sign by the dryer and the wall connector advising not to charge a car while drying clothes. Not exactly idiot proof but might provide a little more breathing room before risk tripping the main.
A "smart" dryer cord would be a cool Tesla accessory. It could communicate with the wall connector and effectively do that transfer without the dryer and the wall connector having to be colocated.
Smart to limit to 30A. That heat tape isn’t light on amps either. You might have 10A @240 in heat tape, 20A for dryer, 40A for hot tub, 10A for lights etc., leaving you about 20A for the EVSE, that’s assuming everything is on at same time, which is rare. These are actual estimated draws, not breaker ratings of course. A 100A breaker won’t pop for intermittent loads around 110A.
Looks like for that the EVSE and the dryer need to plug into the same box. What if the dryer is nowhere near the garage?
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