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DucRider

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Max continuous (>2 hours) is 80% of the circuit rating, thus 40A limit for 50A circuit and 48A limit for 60A circuit.
Just to be clear, an EVSE is always considered a continuous load and the circuit needs to be sized accordingly. There is no exception for shorter charge times.





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azbill

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Amen to all that. I'm doing a similar project and the big question is not which EVSE are going in but where. What I'd definitely like to know from Rivian is where on the car the charge ports are so I can know where to run cable for EVSE. WRT that I'm telling the contractor to run 6/3 to all the likely spots in the gargage and just leave loops for now. When I know where the HPWC go I'll install them there and put 14-50R's at the other cable ends. Hence the neutral which is not needed for EVSE.
If you know where you are going to park the Rivian, then it should be easy to place the charger wires. Most of these chargers have 25 foot cables. Just put the charger near the front center of where you are parking it and that is no problem. FYI, you cannot use 14-50Rs if you are planning on 48A charging, you need a 60A circuit that will be hardwired to the charger. Just tuck some extra wire into a covered box when you install the circuit.
 

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A couple of corrections here

I am not sure this has been brought up on this thread yet, but if you are going to charge at 48A, then the entire circuit must be rated at 60A. That means 60A breaker, 6AWG wire and hardwired.
It is not sufficient that the wire be AWG 6. The wire size is determined by its ampacity as given in tables in the NEC. You may not use 6 NM-B, for example, because it is not rated for 60A, You need something like SE or THHN which have higher temperature ratings so that No. 6 is sufficient. There is also a wire size requirement based on length of run to insure that voltage delivered to the load at the end of the run is within a tolerable drop relative to the panel.

40A limit because it is plugged into an existing 50A rated circuit with a NEMA plug. I do not want to burn my house down just to add 8 amps of extra charging.
This isn't a choice. Code requires that the installer limit the amount the EVSE can draw to 80% of the circuit rating. But your house won't burn down.

50A circuit breakers will over heat and trip in 2 hours when running 50A continuous.
No they won't. Thy have a thermal element which is designed to trip if current goes above the breaker rating and stays there too long. This allows, for example, the huge inrush associated with starting, say, a compressor, which may amount to 150 A in a 50 A installation. These bimetal strips are not precision devices and so there is a tolerance band associated with them. A square D residential molded 50 A breaker carrying a continuous load of 50 A may never trip or it may trip 900 seconds after the load is applied. If it is carrying 125% of the rated load (62.5 A) it will trip between 175 and 2000 seconds after that load is applied. If the load is three times the rating (150 A e.g. air conditoner) the breaker will trip in 10 - 35 sec. etc. But it will not overheat. Note that there is also a magnetic trip to shut the thing off within a cycle for the really heavy currents associated with shorts.

48 amps on a 50 A breaker is 96% of rating. The short time line of the trip band is nearly vertical on the trip plot and just kisses the 96% load line so it is likely that your breaker will never trip if you draw 48 A from a 50 A circuit. But suppose you want to be absolutely sure that it will never trip. What do you do? You use a breaker that is rated 125% of 48 A which is, surprise, 60A. That makes the load 80% of the breaker's rating which is well to the left of the trip band on the diagram (https://download.schneider-electric...File_Name=0600DB0105.pdf&p_Doc_Ref=0600DB0105)

The 50A rated NEMA connectors can also overheat and fail under that continuous load, there is potential for arcing and that creates a fire hazard.
Also not true. At least with the NEMA 14- plugs and receptacles. The 30, 50 and 60 A pins (excepting the neutral which isn't used) have exactly the same dimensions. A 60 amp circuit is good for a 48 A continuous load. Thus the 50 amp plug/receptacle is too.

Max continuous (>2 hours) is 80% of the circuit rating, thus 40A limit for 50A circuit and 48A limit for 60A circuit.
I was for years under the impression that 2 hours was the boundary between intermittent and continuous loads so perhaps that was at one time the case. In any event the dividing line is now 3 hours.
 
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ajdelange

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If you know where you are going to park the Rivian, then it should be easy to place the charger wires. Most of these chargers have 25 foot cables. Just put the charger near the front center of where you are parking it and that is no problem.
This is a convenient charging arrangement.
tesla.jpg


One in which the charger was mounted on the wall in front of the car would not be convenient not least because it would require winding and unwinding of the cable when initiating and terminating charge. OK, I'm lazy but I want the EVSE on the same end and same side as the port.

FYI, you cannot use 14-50Rs if you are planning on 48A charging, you need a 60A circuit that will be hardwired to the charger.
The 14-50R would not be used for charging (though they could be). It is just handy having them around.

Just tuck some extra wire into a covered box when you install the circuit.
Don't want boxes. That's one of the reasons I'll be using HPWC. And 14-50R's will go at the unused cable ends (with enough of a loop to enable swapping things around later if necessary). It would probably be a good idea to make it very clear that No. 6 is NOT that easy to work with.
 

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FYI, you cannot use 14-50Rs if you are planning on 48A charging, you need a 60A circuit that will be hardwired to the charger.
He modified his Black Mamba so he can charge at 48A from 30, 40, 50, or 60A circuits by removing the neutral pin on the 14-60P. See his reasoning here:
Also not true. At least with the NEMA 14- plugs and receptacles. The 30, 50 and 60 A pins (excepting the neutral which isn't used) have exactly the same dimensions. A 60 amp circuit is good for a 48 A continuous load. Thus the 50 amp plug/receptacle is too.
The neutral pin is used - even when not needed as a conductor. It is employed as a safety device by configuring different shapes/orientations that prevent plugging in a device that will draw over the rated circuit capacity. Not surprising that WattZilla would not remove it for you. A bit of a leap of faith that because the dimensions are the same (except for the neutral pin) that the rest of the receptacle/plug is identical and capable of handling loads above the rated capacity. From a manufacturing standpoint it may be easier produce them that way - but then again maybe not.
 

ajdelange

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He modified his Black Mamba so he can charge at 48A from 30, 40, 50, or 60A circuits by removing the neutral pin on the 14-60P.
I would never recommend that someone do that. Not to mention that trying to pull 48 A from a 30 A circuit would result in a trip (from the usual molded breaker) as quickly as 70 seconds but not later than 370 sec.

A bit of a leap of faith that because the dimensions are the same (except for the neutral pin) that the rest of the receptacle/plug is identical and capable of handling loads above the rated capacity. From a manufacturing standpoint it may be easier produce them that way - but then again maybe not.
My experience from manufacturing has been that a busbar of a particular dimension has a particular ampacity no matter what color you paint the cabinet it is installed in.
 

ajdelange

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What I try to do here is remove FUD. The statement

The 50A rated NEMA connectors can also overheat and fail under that continuous load, there is potential for arcing and that creates a fire hazard.
represents FUD at its best. I want readers to be aware that there is absolutely no chance that drawing 48 A for 1 hour, 3 hours or 10 hours from a 14-50R receptacle will start a fire (unless it was installed improperly). Code does not permit this and you should not, therefore, do it but if you do it the risk is that the breaker may trip. Its unlikely that it will but 48 A is right on the "never trip" edge for a 50 A breaker. If you can't understand that 14-50 is safe for 48 A because the current carrying components are the same as in a 60A plug you can be reassured by the fact that 14-50 is intended to be used with 50 A breakers.
 
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...nor Energy Star is probably of much value. I wouldn't even think about Energy Star rating for EVSE...
One comment regarding the value of EnergyStar - certain local incentive programs require the EVSE be EnergyStar certified in order to be eligible for the incentive. As far as I know, this is not required for the federal tax credit.
 

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One comment regarding the value of EnergyStar - certain local incentive programs require the EVSE be EnergyStar certified in order to be eligible for the incentive. As far as I know, this is not required for the federal tax credit.
This is true for the $250 rebate being offered by my local electric company. There’s a box on the application to verify that the EnergyStar logo is on the EVSE.
 

ajdelange

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If it is I'm in trouble because I just took the Fed credit on two that are not Energy Star,
 

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If you can't understand that 14-50 is safe for 48 A because the current carrying components are the same as in a 60A plug you can be reassured by the fact that 14-50 is intended to be used with 50 A breakers.
But not with devices that are designated as continuous use. This requirement was not randomly inserted into the NEC. Nor were EVSEs randomly singled out to carry the continuous use designation.
The breaker will not trip if wiring/connections upstream overheat. Yes, there is a significant buffer built in to only using 80% of the rated circuit capacity and drawing more than that will work fine - right up until the time it doesn't (and when it doesn't a tripping breaker is not the issue to be concerned about).
I know many, many people that used to run massive amounts of Christmas lights for years (pre LED days) off of extension cord snake nests and multiple outlet strips. I know of only a few that had fires as a result. Fewer still had their entire house burn down. I worked for a software company that produces a content valuation program for insurance companies. We went out in the field and did inventories after fires and in many cases the cause was electrical. Sometimes it was a system/component failure, but most often it was improper wiring or other unsafe practices.
 

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The 80% rule for continuous loads goes both ways. An outlet designed for 50A is engineered to not fail at 125% of the rated current, meaning if you were running 62.5A through it, you should have no issues besides excess heating. That said, it's definitely not advisable to exceed 80% of 50A continuous on the outlet because the additional heat involved can cause issues from repeated heat cycles over many uses. If your house burns down and they found out that it was because of a 48A continuous load on a 50A outlet your insurance company might not be willing to pay.
 

ajdelange

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The breaker will not trip if wiring/connections upstream overheat.
You don't seem to grasp that breakers are intended and designed to protect downstream wiring. Not anything upstream and not anything plugged in.


Yes, there is a significant buffer built in to only using 80% of the rated circuit capacity and drawing more than that will work fine - right up until the time it doesn't (and when it doesn't a tripping breaker is not the issue to be concerned about).
When it does, of course, the breaker will trip. I'm curious as to what sort of consequences you anticipate arising after 3:00 that aren't there before 3:00.

I know many, many people that used to run massive amounts of Christmas lights for years (pre LED days) off of extension cord snake nests and multiple outlet strips. I know of only a few that had fires as a result.
This illustrates an apparent paradox. Faulty equipment or improperly installed equipment is less well protected by a breaker rated at 125% than one rated at 100%. An EVSE intended to draw 48 amps, if it experiences some kind of fault causing its draw to increase to 56 A (1.9 kW heat that isn't supposed to be produced is now being produced), is better protected by a 50A breaker than a 60A one as the 50 A breaker will trip (even if it takes it a few minutes to do so) but the 60A will not. But, and I suppose this is the practical message here, there is no paradox as the panel breaker is not intended to protect the equipment plugged in. It is intended to protect the wiring up to the receptacle. It is up to the equipment manufacturer to protect the equipment against internal faults and in order to obtain UL or other agency listing he must do that.

Now if you have a 50 Amp outlet (14-50R) wired to a 50 A breaker you can plug anything that draws up to 50 A into it quite compliant with code as long as you never leave it on for more than 3 hours at a time. Why can't you do this with EVSE? Because EVSE is defined as being a continuous load even when it isn't and that's obviously because it is often on for more than 3 hours. But clearly the perceived threat to your wiring that arises after 3 hours of fuil load draw isn't there if you unplug after 3 hours. So if you are traveling and plug into a 14-50R at a campground with a 48A charger (these are getting hard to find but there are still a fair number of them out there) you need not fear that you will find the place burned down if you return after being gone for 2:45 nor, realistically, do you need to fear that you will find cinders in the morning if you charge overnight.
 
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DucRider

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So it only becomes a hazard after two hours, 59 minutes, and 59.999999999999999999999999 seconds?
What changes at 3 hours to create the hazard?
It the breaker doesn't trip - it's all good? This is often the case in electrical fires. The breaker doesn't sense heat buildup in the wiring/receptacles, doesn't rip and bad things happen.
On another forum (not Rivian related), there was a post about someone that wired a 5-15 in his garage for 240V so he could plug his OEM charge cord in (many work at 120 or 240). Claimed that since the receptacle was rated for up to 250V it was not an issue. Also said it was not unsafe because he lived alone and would always know not to plug a 120V device into that particular outlet in his garage.
I also know of someone that removed the neutral pin from a plug on a device so that it could be plugged into receptacles and circuits rated to handle far less than the device would draw. Claimed it was not a problem because the circuit breaker would trip in xx to xx seconds if the over current became an issue. Said the device met CUL standards "except for one little thing".
Everyone has the choice on obeying codes (or not). Almost always, ignoring them has enough of a buffer that nothing bad happens. Breakers fail, heat cycles can induce additional resistance in connections, repeated plugging/unplugging causes wear and potential increased resistance. The NEC takes all of these factors (and more) into account. But some folks know that code requirements and safety standards like the NEC and UL/CUL are nonsense and it is safe to ignore them.
 

azbill

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It the breaker doesn't trip - it's all good? This is often the case in electrical fires. The breaker doesn't sense heat buildup in the wiring/receptacles, doesn't rip and bad things happen.
The reason I originally brought up the overheat issue, which was claimed to be FUD, was that this very thing happened in my house. I had a 120V wall outlet, with nothing plugged into it, melt down arch and leave burn marks on my drywall. This outlet was daisy chained with other outlets and a chandelier in my dining room. The breaker did not trip until after the arcing/small fire. That circuit had been working fine for 18 years, and the fire department told me I was lucky it had not been worse. The outlet itself was melted, as well as the insulation on one of the wires in the wall.
 

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