If load calculation is 121A on a 125amp supply with TWC included, is that ok?

[terminally_chi]

Hello everyone,

I'm planning to install a Tesla Wall Charger (48A) at my home. My main breaker is 125A. Got a few quotes from various electricians and they all came back to me with various prices and solutions. I'm hoping you could help me out:

• Electrician 1 (who I'm leaning toward to): say my full house load including the EV is 121A, which comes a little too close to 125A. To install just a charger is around $1000, but they strongly suggest adding a Tesla Neurio Kit, which is a load monitoring/meter that can communicate to the charger to lower its output as needed. The total quote is $1800
• Electrician 2: says my full load is well below my main supply, can do it for $1056. Haven't heard back since I request the load calculation
• Electrician 3: Installation is $1000, but says they need to install a DCC Load Balancing unit ($1500) to "acquire full 60A charging" and pass inspection, total is about $2500
• Electrician 4: Need to install a "125a smart switch" next to the breaker panel, then feed the smart switch with 2-pole 60A breaker then to the charger. Says they need this to pass inspection. Quote is $2000

It's a bit wild to me that each electrician company comes up with different solutions. I was expecting they all have a similar scope of work, just different prices.

I did some load calculation myself based on this guide - How Much Electricity Do I Need for My Home? and got 93.8A without the Charger, and 117A with the charger included. I talked with the Electrician 1 and he told me he did optimal calculation method at first, but said that per code - for 125A supply, if the load result is below 100A, they can't use it. So he opt for a standard method (using sq footage of the house *3 and some other numbers). Also said that if I don't want to use the Neurio kit, they can do it without, and it will pass inspection, just that the kit option would be a better and safer choice

Who would you go with in this case? For the record, I don't really use my oven (40A breaker), maybe 1-2 times a year and I'm planning to only charge from 12am - 6am, so no dryer running as well. My stove and heat are gas. I'm wondering if I really do need a meter or load balancing unit for my use case. Should I be worry about only 4A buffer between my load and the supply? or am i worrying over nothing here? Anyone with a 125A main panel can help shed some light here?

I'm located in WA, US if that helps

tl;dr: main panel is 125A, full load calculaton is 117-121A, will i be ok?

 

[Eric33432]

Thank you all for your replies. I think I will go ahead with installing a 60a circuit for my charger, but limit my car charge to 40a instead of 48a for my peace of mind. Because even with 48a enabled with everything running at once, I'm at 121a total, which still below 125, I guess I'm just a bit paranoid about this.

Now that I see your panel, you have a couple of good things going for you:

1. The panel looks to be fairly new, therefore it should be in great condition, no corrosion, etc.

2. You have only two other 240 volt loads. While I would install a 50 amp circuit, you will probably be OK with a 60 amp.

3. Keep in mind those other 240 volt loads are intermittent. They will, on average, not draw anywhere near the number of the amps shown on the breakers.

Since the panel is full, it looks like you will need to free up two spaces by consolidating four 120 volt circuits onto two tandem breakers?

As said before, you really can't rely on using the setting in the car or app to dial down the amps.

While the electrical code does not allow you to say you will only charge when you are not using the dryer, oven, etc., in reality you can do that.

Once this is all working, your "charging anxiety" will soon be gone and you will be surprised that when you charge overnight, it does not matter if you are charging at 32, 40, or 48 amps. Even when my Model X (the slowest charging Tesla) is down to 30%, it only takes about 5 hours to be back to 80% at 48 amps. Only a problem (and just a slight problem) if you are way down and need to recover quickly for another trip within a few hours of arriving with a low state of charge, and unless that is something you do frequently it will not be the end of the world if you have to leave on your trip with, say, only 50% SOC and have to hit a Supercharger earlier than you otherwise would do.

Even at 24 amps it would likely be OK. Once when visiting a friend, and arriving at his house at 8%, I used my mobile connector to charge from his dryer outlet at 24 amps, and by the next morning was back to 80% after about 16 hours of charging.

Hope all this helps. Thanks for reading.

 

[GSP]

@terminally_chi - I am not an electrican, but I recommend getting an electrician to do a careful load calculation to see if your panel can accept a 60 A breaker or not. If not, a 50 A breaker should be more than you will ever actually need.

I have two Teslas, each on a 20 A 240 V circuit. This limits charging to 16 A for each car, and they both are always fully charged in the morning. Even when I leave at 5:30 am. Occasionally when I return late at night from a road trip at 20-30% SOC, the car will not be fully charged to my 80% set point when I leave the next morning. However it still has plenty of range for my daily driving, and catches up to my 80% charge limit the next evening.

Based on my experience, 24 A charging (30 A breaker) is sufficient for most drivers (~98%), and 40 A charging (50 A breaker) should work fine for anyone, IMO. Don't fret about not having 48 A charging at home.

Good Luck with your install,

GSP

 

[tls]

It's unlikely that your electric service from the utility is actually 125A. Are you sure you don't have a 125A panel on a 200A service? If so, installing a separate 200A service switch, probably near the meter, to feed the panel and a charger is the right way to do this.

 

[Eric33432]

I'd like to know the actual numbers you used for each of these steps, out of curiosity. I'm getting much larger numbers than you seem to be.

I always recommend running a load study. While I cannot know all the details, by looking at the photo of the panel I know the only 240 volt loads are the oven and the dryer. I assumed 2500 square feet, accounted for the appliances shown on the panel, and there is no electric heat or central air, and added a 48 amp EVSE and came up with 90 amps. This is using Mike Holt's Electric Tool box app, which uses the optional load study. The metrics that are used are shown below.

Now that I see this, unless there is something that is not disclosed by looking at his panel, or he is way over 2500 square feet, I think he is OK with a 60 amp EVSE circuit for 48 amp charging, and it does not matter if he is charging during a time when the dryer is in use, etc.

If you see something different, or disagree please chime in! Unfortunately the Mile Holt app only does the optional load study, perhaps you are using the calculations that would be done in the NEC's regular load study? (I see after I ran this I should have included a few amps for furnace blower motor, but that would not change the result.)

USER INPUTS​

A. General Lighting/Receptacles:

Living Area in Sq. Ft.:

2500sq. ft.

Small Appliance Circuits: 2 Circuits

Laundry Circuit(s): 1 Circuit(s)

B. Fixed Appliances and Equipment:

Dishwasher(s), 120V:1Unit(s),15 Amperes

Disposal(s), 120V:1Unit(s),15 Amperes

Electric Vehicle Charger(s), 240V:1Unit(s),48 Amperes

Microwave(s), 120V:1Unit(s),1800 VA

Electric Dryer(s), 240V:1Unit(s),5000 VA

Oven Single(s), 240V:1Unit(s),5000 VA

C. Cooling/Heating Load(s):

Cooling Load: AC/Condenser
0A and Fan 0A, 240V

Heating Load: Heat
0 VA and Fan 0A, 240V

COPPER RESULTS​

1. Service Disconnect Rating: 100A
2. Service Conductor Size:
4 AWG, rated 85A at 75°C
3. Service Neutral Conductor Size: 4 AWG, rated 85A at 75°C
4. Supply-Side Bonding Jumper: 8 AWG
5. Raceway Size: 1¼ Inch

ALUMINUM RESULTS​

1. Service Disconnect Rating: 100A
2. Service Conductor Size: 2 AWGAL, rated 90A at 75°C
3. Service Neutral Conductor Size: 2 AWGAL, rated 90A at 75°C
4. Supply-Side Bonding Jumper: 6 AWGAL
5. Raceway Size: 1¼ Inch

Service Calculation[220.82(B)]

A. General Lighting/Receptacles:

Living Area: 2500 x 3 VA = 7500VA

Small Appliance Circuits: 1,500 VA x 2 = 3000VA

Laundry Circuit(s): 1,500 VA x 1 = 1500

B. Fixed Appliances and Equipment

Dishwasher(s), 120V:1Unit(s) x 15 Amperes x 120V =1800VA

Disposal(s), 120V:1Unit(s) x 15 Amperes x 120V =1800VA

Electric Vehicle Charger(s), 240V:1Unit(s) x 48 Amperes x 240V =11520VA

Microwave(s), 120V:1Unit(s) x 1800 VA = 1800 VA

Dryer 1Unit(s), 5000VA

Oven Single(s), 240V:1Unit(s), 5000VA

Subtotal: 38920VA
First 10,000 VA at 100%: 10000

Remainder 28920 VA at 40% = 11568 VA

Subtotal Demand Load: 21568 VA

C. Cooling/Heating Load(s) [220.82(C)]:

Cooling Load at 100%: 240V x (0A + 0 A) = 0 VA

Heating Load at 65%: [0VA +(240V x 0 A)] x 65% = 0 VA

Cooling/Heating Demand Load: 0 VA

Total Service Demand Load:

Service Demand VA Load (A, B, and C):21568 VA

Service Load in Amperes: 90A ( 21568 VA/240V)

NOTES:​

1. Service Disconnect Rating [240.4 and 240.6(A)]

Service disconnect sized must have an ampacity of at least 90A

Service Disconnect Rating: 100A

2. Service Conductor Size [310.15(B)(7) and Table 310.15(B)(16)]

Service conductor sized to 83% of 100A service disconnect rating.

100x 83% = 83A

3. Service Neutral Conductor Size [220.61 and Table 310.15(B)(16)]

A. General Lighting, Small Appliance, and Laundry VA Load: [220.42]

General Lighting: 2500 sq. ft. x 3 VA = 7500 VA

Small Appliance Circuits: 1,500 VA x 2 = 3000 VA

Laundry Circuit(s): 1,500 VA x 1 = 1500 VA

First 3,000 VA at 100% = 3000 VA

Remainder, 9000 VA at 35% = 3150 VA

General Lighting, Small Appliance, and Laundry Demand Load: 6150

B. Appliance(s) VA Load:​

Dishwasher(s), 120V:1Unit(s) x 15 Amperes

Total: 5400 VA x 75% = 4050 VA, 220.53

Disposal(s), 120V:1Unit(s) x 15 Amperes

Total: 5400 VA x 75% = 4050 VA, 220.53

Microwave(s), 120V:1Unit(s) x 1800 VA

Total: 5400 VA x 75% = 4050 VA, 220.53

C. Dryer(s) VA Load [220.60]​

Neutral Demand Load [220.61(B)]​

5000VA x 70% = 3500 VA, 220.54

D. Cooking Equipment VA Load [220.61] and Table 220.55​

Neutral Demand Load [220.61(B)]​

0 VA x 70% = 0 VA, 220.55

Neutral VA Demand Load(A, B, C, and D)​

6150 VA + 4050 VA + 3500 VA + 0 VA = 13700 VA

Neutral Load in Amperes:

57A ( 13700 VA/240V)

4. Supply-side Bonding Jumper Size [250.102(C)]​

Supply-side bonding jumper sized to the service conductor size.

5. Raceway Size [Chapter 9, Table 1]​

Based on a raceway at 40% fill, with an equipment grounding conductor.

 

[davewill]

This is why I suggested he install a 60a circuit and back off to a 50a (or 40a) breaker only if the inspector refused to pass it. I think he'll probably be fine and pass inspection.

 

[Cosmacelf]

Since the panel is full, it looks like you will need to free up two spaces by consolidating four 120 volt circuits onto two tandem breakers?

Why do you say his panel is full? There's a tandem slot bottom left unused.

 

[Eric33432]

Why do you say his panel is full? There's a tandem slot bottom left unused.

That slot is not available. The 125 amp main breaker also uses that slot. See, it says "Do Not Remove" the twist outs!

 

[Cosmacelf]

That slot is not available. The 125 amp main breaker also uses that slot. See, it says "Do Not Remove" the twist outs!

Are you sure about that? 125 amp breakers can fit in one tandem slot. Regardless, quad breakers are easy to add.

 

[Eric33432]

Are you sure about that? 125 amp breakers can fit in one tandem slot. Regardless, quad breakers are easy to add.

Perhaps I should not have said the 125 amp breaker "uses" the slot opposite, but in many panels like this that have a breaker that back feeds the panel, the 125 amp main breaker fits in a special space and the stabs the breaker plugs on to are limited to the single 125 amp breaker so no breaker can be installed opposite the main breaker, which in this type of panel is basically just a back feed into the panel. These breakers also usually have some mounting mechanism or hardware that make them difficult to remove.

Some panels also have limitations on the total amps allowed on any row. For example, you could not have breakers totaling more than say 125 amps on any single row.

I don't like to install high amp breakers opposite one another. For example I would not put two 9,600 watt electric heat circuits opposite each other. I have seen stabs to which high amp breakers are plugged on to burn up more than once. I definitely would not install an EVSE providing 11,500 watts of power opposite the main breaker which is also carrying that 11,500 watts, plus all the other loads in the panel, even if there were no restrictions for that panel.

Perhaps the OP can confirm if I am correct.

I would recommend a full size breaker for the wall connector, not a quad, and using two 120 volt tandems to reclaim the space for it.

 

[ATPMSD]

Look at the sticker on the inside panel door, this should tell you what you can and cannot do.

 

[terminally_chi]

Perhaps I should not have said the 125 amp breaker "uses" the slot opposite, but in many panels like this that have a breaker that back feeds the panel, the 125 amp main breaker fits in a special space and the stabs the breaker plugs on to are limited to the single 125 amp breaker so no breaker can be installed opposite the main breaker, which in this type of panel is basically just a back feed into the panel. These breakers also usually have some mounting mechanism or hardware that make them difficult to remove.

Some panels also have limitations on the total amps allowed on any row. For example, you could not have breakers totaling more than say 125 amps on any single row.

I don't like to install high amp breakers opposite one another. For example I would not put two 9,600 watt electric heat circuits opposite each other. I have seen stabs to which high amp breakers are plugged on to burn up more than once. I definitely would not install an EVSE providing 11,500 watts of power opposite the main breaker which is also carrying that 11,500 watts, plus all the other loads in the panel, even if there were no restrictions for that panel.

Perhaps the OP can confirm if I am correct.

I would recommend a full size breaker for the wall connector, not a quad, and using two 120 volt tandems to reclaim the space for it.

I just talked with electrician 1 and he said that the 2 bottom left slots are also used for the main breaker (something to hold/mount the main line), so we can't use that. They're going to consolidate the dryer and oven into one breaker, and use the new open slot for the charger. Is that similar to what you're suggesting?

 

[ATPMSD]

I just talked with electrician 1 and he said that the 2 bottom left slots are also used for the main breaker (something to hold/mount the main line), so we can't use that. They're going to consolidate the dryer and oven into one breaker, and use the new open slot for the charger. Is that similar to what you're suggesting?

Seems like an odd solution, not ever sure if that is code, but I am not an electrician. How about this:

As I look at your photos nearly all of the breakers seems to be GFCI, but I do not think GFCI is required unless the outlet is going to a potentially wet environment, such as a bathroom. So then, if you take the top four 15a breakers and on the right side and replace them with two standard tandem breakers, this should free up two slots in which you could then add a 50a or 60a 240v breaker.

 

[Sophias_dad]

Seems like an odd solution, not ever sure if that is code, but I am not an electrician. How about this:

As I look at your photos nearly all of the breakers seems to be GFCI, but I do not think GFCI is required unless the outlet is going to a potentially wet environment, such as a bathroom. So then, if you take the top four 15a breakers and on the right side and replace them with two standard tandem breakers, this should free up two slots in which you could then add a 50a or 60a 240v breaker.

Good point about the GFCI/AFCI(Blues are AFCI/GFCI, Greens are just AFCI). They probably aren't available in tandem, and that's probably why the electrician is combining the dryer/range. That said, I'd probably combine the dryer/EV or range/EV so you don't have to go screwing with crossing the wires from one side to the other to make the dryer/range combo.

I'm pretty sure AFCI is required in bedrooms now, btw.

 

[ATPMSD]

I'm pretty sure AFCI is required in bedrooms now, btw.

What is really interesting is the top breaker on the left is a tandem with one breaker going to a “bath” and I am pretty sure that requires a AFCI or AFCI/GFCI breaker!

 

[Sophias_dad]

What is really interesting is the top breaker on the left is a tandem with one breaker going to a “bath” and I am pretty sure that requires a AFCI or AFCI/GFCI breaker!

I'd wager that for that one circuit they have in-the-plug GFCI, so they can easily reset it if their hair dryer falls in the tub.

 

[terminally_chi]

Talked with electrician #5 today and he said the same thing as electrician #1 that I don't need a power management. And will likely put a quad breaker to consolidate the range+dryer, then a separate 60a for the charger

Also just found out that my oven use gas and only use a 120v 15a to power its basic electric function stuffs so I guess I was just worrying over when pigs have wings and now all good for the full 48a charger installation.

 

[Sophias_dad]

Talked with electrician #5 today and he said the same thing as electrician #1 that I don't need a power management. And will likely put a quad breaker to consolidate the range+dryer, then a separate 60a for the charger

Also just found out that my oven use gas and only use a 120v 15a to power its basic electric function stuffs so I guess I was just worrying over when pigs have wings and now all good for the full 48a charger installation.

In that case I have a better solution. Have the electrician put in a tandem breaker(20/20) at the top of that the right column, move the one used hot connector for the oven to it, and use the oven duplex spot for the EV.

 

[Eric33432]

I just talked with electrician 1 and he said that the 2 bottom left slots are also used for the main breaker (something to hold/mount the main line), so we can't use that. They're going to consolidate the dryer and oven into one breaker, and use the new open slot for the charger. Is that similar to what you're suggesting?

That would work fine.

In response to some of the other answers to your question, I agree the best option would be to convert the oven circuit to a 120 volt circuit and put it on a tandem breaker with another circuit that does not need GFCI/Arc Fault protection if that is possible. And you cannot combine the top 4 breakers on the right side into two tandem breakers, because your bed rooms require AFCI breakers.

But combining the dryer with the existing 240 volt oven circuit is perfectly fine too, and it might just be simpler and less work to do it that way than having to mess with the other end of the oven circuit.

While OK if it is the only thing you can do, I do not like putting high current circuits on tandem breakers, so I would not combine the EVSE circuit on a tandem breaker with another 240 volt circuit. It is best to put high amp circuits on non-tandem breakers whenever possible. Oven and dryer loads are intermittent and nothing compared to a circuit that draws 48 amps for long periods of time.

While everything was good before, removing that oven load from the load study I did for you tells me you will be more than fine for 48 amp charging. If everything is OK feeding your panel, you should not even need to worry about dialing it back.

Just be sure your electrician uses the correct size wire. Many electricians are used to using #6 NM-B cable on 60 amp circuits for 9,600 watt electric heat, which is fine because even with the air handler blower motor such circuit will draw less than 55 amps and are not considered a continuous load. This is not OK on a 48 amp circuit EVSE circuit which is considered a continuous (more than 3 hour) load as #6 NM is only good for 55 amps non continuous and 44 amps continuous.

Wire needed is #6 THHN/THWN installed in conduit (with #10 ground) or 6/2 MC cable, which is easier to install than conduit in many installations. If installing NM (Romex) cable (not recommended), please ensure he uses #4. Unfortunately, #4 NM is only available in three conductor (plus ground), so it is more expensive and more difficult to install due to it being harder to bend, etc.

Good luck with your installation!

 

[davewill]

That would work fine.

In response to some of the other answers to your question, I agree the best option would be to convert the oven circuit to a 120 volt circuit and put it on a tandem breaker with another circuit that does not need GFCI/Arc Fault protection if that is possible. And you cannot combine the top 4 breakers on the right side into two tandem breakers, because your bed rooms require AFCI breakers.

But combining the dryer with the existing 240 volt oven circuit is perfectly fine too, and it might just be simpler and less work to do it that way than having to mess with the other end of the oven circuit.

...

I would not remove the existing 240v oven circuit. Someone may wish to install an electric oven at some point in the future.

 

[ATPMSD]

And you cannot combine the top 4 breakers on the right side into two tandem breakers, because your bed rooms require AFCI breakers.

Why not just install a AFCI outlet to get around that? Seems like that is what was done for the “bath” tandem breaker at the upper left.