Quick electrical wiring question, derating break for Level 2 charger

[TT_Vert]

I'm not going to run this as I cannot easily bend 1" EMT so i'll leave it to the pros. Anyway the run is less than 40'. I am having them run 4AWG THHN to a service disconnect. THHN is rated at 95A derated to 76A for continuous use. I am only running 3 current conductors and have no thermal derate so I should be good w/a 70A breaker based on my calcs. What is throwing me is that I am reading about people derating their breaker. In essence people w/ 60A breakers are saying they can only charge at 48A. Is this because they are ASSUMING (rightfully so) that the wiring is the bare minimum for a 50A NON continuous load? This would make sense to me but I just wanted to confirm. In my case, knowing my derates and running the appropriate breaker for them (70A) I could safely run a continuous 70A load correct? I won't be doing that but I may be using two 30A chargers at some point.

Thanks much,

Dave

 

[mm08822]

Continuous loads require ampacity of conductors and CB to be 125% of load. 60A = 125% of 48A. #6 CU NM-B @60C =60A.

In your case, I would suggest put a sub panel in and let the future need (when it becomes real) determine the branch circuits from the sub.
I would use aluminum xhhw instead of $$$ Copper. Using AL would also give you opportunity for larger conductors at lower cost. You don't need a full size neutral either.

If your future loads were actually 2 x 30A EVC's (with possibility to full charge at same time), then you would need a min of 75A ampacity conductors and 80A cb. #2 AL XHHW would allow for 90A on a 90A cb feeding a sub-panel allowing for greater future value to feed other random loads.

 

[TT_Vert]

Continuous loads require ampacity of conductors and CB to be 125% of load. 60A = 125% of 48A. #6 CU NM-B @60C =60A.

In your case, I would suggest put a sub panel in and let the future need (when it becomes real) determine the branch circuits from the sub.
I would use aluminum xhhw instead of $$$ Copper. Using AL would also give you opportunity for larger conductors at lower cost. You don't need a full size neutral either.

If your future loads were actually 2 x 30A EVC's (with possibility to full charge at same time), then you would need a min of 75A ampacity conductors and 80A cb. #2 AL XHHW would allow for 90A on a 90A cb feeding a sub-panel allowing for greater future value to feed other random loads.

Thanks for the reply. I'm a bit confused by this. 4AWG THHN is rated at 95A derated to 76A for continuous use. The breaker should be sized to protect the conductor (70A) no? I'm already derating per NEC, why the second derate?

Dave

 

[mike93lx]

I'm a bit confused by this. 4AWG THHN is rated at 95A derated to 76A for continuous use. The breaker should be sized to protect the conductor (70A) no? I'm already derating per NEC, why the second derated??

Dave

No need to "derate" a breaker. That 95a rating is at 90 degrees c, so everything in the circuit has to be rated for it. 75 degrees gets you 85a.

I'd breaker it at 80a, then you can draw up to 60a continuous.

2al xhhw would be a bunch cheaper and you can breaker at 90

 

[TT_Vert]

No need to "derate" a breaker. That 95a rating is at 90 degrees c, so everything in the circuit has to be rated for it. 75 degrees gets you 85a.

I'd breaker it at 80a, then you can draw up to 60a continuous.

2al xhhw would be a bunch cheaper and you can breaker at 90

So to clarify, the 75C limitation of the breaker is further derating the ampacity? There is no 90C breaker? I don't have a fill chart handy but to go 2AWG they may need to further increase the EMT.

Dave

 

[mike93lx]

You are leaving out a egc, right?

The 75 I used is a degrees C rating, not amperage.

I have no idea what the ratings are on your breakers, but how about the EVSE you are connecting? Assuming a 75 degree rating should be a safe bet

 

[cybrdyke]

I won't be doing that but I may be using two 30A chargers at some point.

Thanks much,

Dave

You mean two 32A chargers, I think. Each of those will require 40A infrastructure.
CD

 

[TT_Vert]

You are leaving out a egc, right?

The 75 I used is a degrees C rating, not amperage.

I have no idea what the ratings are on your breakers, but how about the EVSE you are connecting? Assuming a 75 degree rating should be a safe bet

Sorry yes,, 75C. There is no circuit in place yet. Just trying to get an idea of the best way to try to future proof this a bit. #2 AL XHHW may be the best way depending on cost.
Spoke with the potential contractor and this is one thing he said which seemed odd to me. It seems he's saying he cannot run a larger wire/ breaker than the device requires. Am I misinterpreting this?

"Additionally, We cannot overfeed a device that’s dedicated to a singular device such as charger. If that single item which is hardwired requires 50amp max than we cannot give it a 75 amp breaker. This is both manufacturer specification and NEC."




Dave

 

[mike93lx]

Sorry yes,, 75C. There is no circuit in place yet. Just trying to get an idea of the best way to try to future proof this a bit. #2 AL XHHW may be the best way depending on cost.
Spoke with the potential contractor and this is one thing he said which seemed odd to me. It seems he's saying he cannot run a larger wire/ breaker than the device requires. Am I misinterpreting this?

"Additionally, We cannot overfeed a device that’s dedicated to a singular device such as charger. If that single item which is hardwired requires 50amp max than we cannot give it a 75 amp breaker. This is both manufacturer specification and NEC."




Dave

If the device calls for a 50a max breaker, that is what you need to do.

I'd really consider a small sub panel. A little 6 circuit will give you some flexibility plus allow you to drop wire size to match the devices you are installing. They're also pretty cheap

 

[mm08822]

The sub-panel is a great way to change wire size, material and breaker rating. Not every charger will accept Aluminum conductors. The sub panel let's you run shorter lengths of copper to reach the charger.

You can use SER 2-2-4-6 AL to feed the sub. What is the need for emt?

 

[TT_Vert]

The sub-panel is a great way to change wire size, material and breaker rating. Not every charger will accept Aluminum conductors. The sub panel let's you run shorter lengths of copper to reach the charger.

You can use SER 2-2-4-6 AL to feed the sub. What is the need for emt?

That's A great question! I thought our code required this on EMT. If it doesn't that's an easy run. I'll have check.

Dave

 

[beemerphile]

48-50 amps is about the max for any Level 2 chargers I have seen. If you are going to run a larger service I agree with the sub-panel suggestion and then an appropriate breaker and circuit to any chargers to decide to install. That is what I did for my Tesla Wall Charger.

 

[mike93lx]

That's A great question! I thought our code required this on EMT. If it doesn't that's an easy run. I'll have check.

Dave

I believe Chicago requires emt. That's definitely not the norm though

 

[mm08822]

I believe Chicago requires emt. That's definitely not the norm though

If this is Chicagoland, 2-#2's and 1-#4 will fit in 1". Use the conduit as the EGC. (I would expect the Chicago boy's to be artists at running conduit so it should be a primo emt install.)

 

[TT_Vert]

If this is Chicagoland, 2-#2's and 1-#4 will fit in 1". Use the conduit as the EGC. (I would expect the Chicago boy's to be artists at running conduit so it should be a primo emt install.)

Yeah i'm sure it's second nature to them. I did 1/2" when I finished my basement and it's quite the artform

I believe Chicago requires emt. That's definitely not the norm though

Sadly, I think that's the case. She's in a suburb so I'll see what version of NEC they follow.

48-50 amps is about the max for any Level 2 chargers I have seen. If you are going to run a larger service I agree with the sub-panel suggestion and then an appropriate breaker and circuit to any chargers to decide to install. That is what I did for my Tesla Wall Charger.

Yeah I may end up going this route depending on what my SIL decides. I really wanted to have the ability to expand later if she wanted to. 6AWG doesn't allow that at all. I don't know how soon EV charging will evolve to a higher charging current but I wanted to have a setup in place to allow that if it does..

 

[mike93lx]

I doubt we will see higher than 48a charging being mainstream for a long time. With the way home chargers are used, and the typical infrastructure we have, it works great. Plus it's already at the top end of what equipment tends to draw at a home, so getting into 80+a charging circuits would be a big change from what we are used to.

If you put in a 80-90a feed to a subpanel, I bet you will comfortably be within what you'll need in the lifespan of the house's electrical system. That can comfortably do two cars

 

[TT_Vert]

I doubt we will see higher than 48a charging being mainstream for a long time. With the way home chargers are used, and the typical infrastructure we have, it works great. Plus it's already at the top end of what equipment tends to draw at a home, so getting into 80+a charging circuits would be a big change from what we are used to.

If you put in a 80-90a feed to a subpanel, I bet you will comfortably be within what you'll need in the lifespan of the house's electrical system. That can comfortably do two cars

Thanks, i'm not an EV guy in the least so I have no idea on the actual movement towards faster charging.

Dave

 

[beemerphile]

Faster is only needed on the road. At home if you can go from 10% to 80% overnight that’s about all you’d need it to do. Faster charging is harder on the battery as well. You want the slowest charge that will get it done in the time you have. Most people are well served with a NEMA 14-50 charging circuit and will be for a long time.

 

[TT_Vert]

They are using their level 1 charger now and they want a quicker charge for whatever reason. They have an ID4 and i don't think the range is all that great. She's an older lady who wants to ensure it's charged when she needs to go out.

Dave

 

[TT_Vert]

No need to "derate" a breaker. That 95a rating is at 90 degrees c, so everything in the circuit has to be rated for it. 75 degrees gets you 85a.

I'd breaker it at 80a, then you can draw up to 60a continuous.

2al xhhw would be a bunch cheaper and you can breaker at 90

How can I breaker #2 AL XHHW at 90A? It seems it's rated at 100A @90C so derated for continuous use would be 80 no?

 

[mike93lx]

How can I breaker #2 AL XHHW at 90A? It seems it's rated at 100A @90C so derated for continuous use would be 80 no?

No. There is an asterisk on that 100a. It's only allowed at 100a when it is feeding the entire load of a dwelling. Outside of that, it's 90a.

Also, you can always reduce a breaker beyond the max for a conductor

 

[TT_Vert]

No. There is an asterisk on that 100a. It's only allowed at 100a when it is feeding the entire load of a dwelling. Outside of that, it's 90a.

Ok so with that don't we have to apply the continuous use derate of 125%? Do we derate from 90?

 

[mike93lx]

Ok so with that don't we have to apply the continuous use derate of 125%? Do we derate from 90?

90 is the max allowable. So derate from there. 72a would be the max for a continuous load

 

[TT_Vert]

90 is the max allowable. So derate from there. 72a would be the max for a continuous load

Right so that'd afford me a 70A breaker, not 90A correct? Or maybe the feed to the sub panel also doesn't need to be derated for continuous use? Maybe I misunderstood where you said "2al xhhw would be a bunch cheaper and you can breaker at 90" above?

Dave

 

[mike93lx]

Right so that'd afford me a 70A breaker, not 90A correct? Or maybe the feed to the sub panel also doesn't need to be derated for continuous use? Maybe I misunderstood where you said "2al xhhw would be a bunch cheaper and you can breaker at 90" above?

Dave

No. 90a breaker, 72a load. The breaker can be "full strength". If you went to a subpanel, you would then install a 60a breaker to feed your 48a EVSE, and use #6 copper thhn. Later you can add another EVSE off that sub, or feed other equipment.

#2 aluminum will be a lot cheaper than #4 copper. Xhhw is the wire type for that aluminum, whereas you would use thhn/thwn for the copper.

The only downside is that the conductor is larger

 

[TT_Vert]

No. 90a breaker, 72a load. The breaker can be "full strength". If you went to a subpanel, you would then install a 60a breaker to feed your 48a EVSE, and use #6 copper thhn. Later you can add another EVSE off that sub, or feed other equipment.

#2 aluminum will be a lot cheaper than #4 copper. Xhhw is the wire type for that aluminum, whereas you would use thhn/thwn for the copper.

The only downside is that the conductor is larger

Quick glance at a fill chart shows I can fit three #2 wires in there so that'd be ok. So the main breaker can be the full allowable ampacity of the conductor? I assume doing this I would set both chargers to 40A?

Thanks
Dave

 

[beemerphile]

Lots of people with multiple chargers sequence them rather than running them at the same time. No need to run two and be through at midnight when you can do them one after the other and still be done by start of day.

 

[TT_Vert]

Lots of people with multiple chargers sequence them rather than running them at the same time. No need to run two and be through at midnight when you can do them one after the other and still be done by start of day.

I suppose but I cannot rely on that. This isn't the case now as they only have one EV but the other who may eventually purchase one is a commercial airline pilot w/ random hours so this won't always apply to them.

Dave

 

[beemerphile]

...They have an ID4 and i don't think the range is all that great. She's an older lady who wants to ensure it's charged when she needs to go out.

Dave

Well, a car with a smaller battery is fully charged faster than a car with a larger battery at a given charge rate. The standard ID4 battery is only 55 kWh.

 

[TT_Vert]

Well, a car with a smaller battery is fully charged faster than a car with a larger battery at a given charge rate. The standard ID4 battery is only 55 kWh.

Yeah I don't know the voltage these things charge at to convert the charge rate to Wh. to calculate charge times so I haven't a clue how quickly her car charges. I just know I was advised that she'd like to charge quicker. This is family so I'm going on the info I was given.

 

[mike93lx]

Quick glance at a fill chart shows I can fit three #2 wires in there so that'd be ok. So the main breaker can be the full allowable ampacity of the conductor? I assume doing this I would set both chargers to 40A?

Thanks
Dave

The neutral can be smaller, #4 is no problem. Not a lot of space saved but it's something. Yes, breaker is full size.

If this was mine, I would probably end up with two set at 48a and set the chargers to not overlap, but I know you mentioned that may not work. Restricting them to both to 32a would work, or maybe you can do one at 48 and one at 32. That said, if you are charging each night, 32a is likely plenty

 

[mike93lx]

Yeah I don't know the voltage these things charge at to convert the charge rate to Wh. to calculate charge times so I haven't a clue how quickly her car charges. I just know I was advised that she'd like to charge quicker. This is family so I'm going on the info I was given.

Output voltage doesn't matter. You know the input: 32a *240v=7680w. That is 7.7kWh. And the battery capacity in the same unit of measure.

The charge rate isn't linear, and you won't be charging from dead, but that likely means you are topping off in a few hours each day

 

[TT_Vert]

The neutral can be smaller, #4 is no problem. Not a lot of space saved but it's something. Yes, breaker is full size.

If this was mine, I would probably end up with two set at 48a and set the chargers to not overlap, but I know you mentioned that may not work. Restricting them to both to 32a would work, or maybe you can do one at 48 and one at 32. That said, if you are charging each night, 32a is likely plenty

Thank much, appreciate the response. Same to everyone else, i understand a bit better now.. One last question, you mention both at 32A but if the main sub panel breaker is 90A (2AWG feed) and both EVC circuits are 50A (6AWG) couldn't i safely set both chargers to 40A? That'd keep me under main breaker current and under each circuits 50A. I'm at the 80% breaker rule as well.

Dave

 

[mike93lx]

Thank much, appreciate the response. Same to everyone else, i understand a bit better now.. One last question, you mention both at 32A but if the main sub panel breaker is 90A (2AWG feed) and both EVC circuits are 50A (6AWG) couldn't i safely set both chargers to 40A? That'd keep me under main breaker current and under each circuits 50A. I'm at the 80% breaker rule as well.

Dave

40+40 is greater than the derating on a 90a circuit. If you had both running at the same time and drawing their full power you'd be in excess of what was allowable. Is that likely to happen? Probably not.

You can tell the evse to limit charging current so you can always set them lower to start and see if it meets your needs. Bump one up if needed.

Either way, 90a should be plenty to keep two cars charged up

 

[TT_Vert]

The neutral can be smaller, #4 is no problem. Not a lot of space saved but it's something. Yes, breaker is full size.

If this was mine, I would probably end up with two set at 48a and set the chargers to not overlap, but I know you mentioned that may not work. Restricting them to both to 32a would work, or maybe you can do one at 48 and one at 32. That said, if you are charging each night, 32a is likely plenty

Do these things cycle between CC and CV like when charging other lithium type batteries? Do they have configurable charge profiles or just charge end battery percentages? I wasn't going to assume the output voltage of charger was 220V. I used to race RC cars and when we charged lithium batteries the current and voltage did change throughout the charge.

Dave

 

[mike93lx]

Do these things cycle between CC and CV like when charging other lithium type batteries? Do they have configurable charge profiles or just charge end battery percentages? I wasn't going to assume the output voltage of charger was 220V. I used to race RC cars and when we charged lithium batteries the current and voltage did change throughout the charge.

Dave

The EVSE is just passing AC power over to the car. The conversion to DC is happening there.

So the output voltage is irrelevant, but it is 240v with a L2. 7.7kwh in means that is what is going out, minus any consumption for the electronics in the EVSE itself

 

[TT_Vert]

40+40 is greater than the derating on a 90a circuit. If you had both running at the same time and drawing their full power you'd be in excess of what was allowable. Is that likely to happen? Probably not.

You can tell the evse to limit charging current so you can always set them lower to start and see if it meets your needs. Bump one up if needed.

Either way, 90a should be plenty to keep two cars charged up

Ok so you must still take into consideration ampacity derating of the feed for continuous use but NOT when sizing the main breaker feeding the subpanel? IE the wire at 75C is 90A so you can use a 90A breaker to feed the sub panel but when in use you have to derate? That confused me a bit.

 

[TT_Vert]

The EVSE is just passing power over to the car. The conversion to DC is happening there.

So the output voltage is irrelevant. 7.7kwh in means that is what is going out, minus any consumption for the electronics in the EVSE itself

Ahh, wasn't aware the car did all charge control. Why are these chargers so expensive then??

Dave

 

[mike93lx]

Ahh, wasn't aware the car did all charge control. Why are these chargers so expensive then??

Dave

They have software to manage the connection, there is hardware involved, and because they can. Broadly, Ev's are still toys of the wealthy. The cars come with plugs that mean a EVSE is not required. It's a convenience and a luxury

 

[TT_Vert]

They have software to manage the connection, there is hardware involved, and because they can. Broadly, Ev's are still toys of the wealthy. The cars come with plugs that mean a EVSE is not required. It's a convenience and a luxury

I could probably program a pi or an arduino to do that part. That's going to bring me down another rabbit hole now..

Dave