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?

 

[Sophias_dad]

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.

I'm not aware of any AFCI outlets, only GFCI. That said, its been a while since I went outlet shopping(at least the electrical kind!)

 

[Cosmacelf]

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?

Yes, that would work. For folks who don't seem to understand these things, this is the kind of breaker the electrician is proposing to use:

Will work fine. Don't do anything to the actual oven circuit, like replacing it with a 15A circuit or anything, just use it like you were before. But as you said, it is nice to know that the oven doesn't draw much current.

And replacing those two breakers will indeed give you room for a 60A breaker. Maybe move a couple of the 20A circuits to be opposite that new quad breaker if possible so you don't load up a single stab too much.

 

[tls]

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.

Under 2017 or later code, 6-6-6 or 6-6-8 copper type SE cable (type SEU or SER but NOT type USE) is another acceptable alternative. It is rated for 65A non-continuous or 52A continuous. This is new for type SE larger than #10 under 2017 and later codes - it was not allowed before.

Not the most common type of cable out there and the SEU in particular is a nuisance for homeowners to work with because you have to know how to neatly spin up the concentric ground strands for termination. But it is 75C rated and can be fished through walls/ceilings, which can save a lot of work running conduit sometimes.

4-4-6 aluminum SE cable is fine too, probably available at your local big-box store, and a lot cheaper than almost any other alternative, but at the charger end, requires an additional junction box, a few split-bolts or Polaris connectors, and a copper pigtail into the charger since modern Tesla chargers are not rated for use with aluminum wire.

 

[terminally_chi]

Yes, that would work. For folks who don't seem to understand these things, this is the kind of breaker the electrician is proposing to use:

View attachment 992455

Will work fine. Don't do anything to the actual oven circuit, like replacing it with a 15A circuit or anything, just use it like you were before. But as you said, it is nice to know that the oven doesn't draw much current.

And replacing those two breakers will indeed give you room for a 60A breaker. Maybe move a couple of the 20A circuits to be opposite that new quad breaker if possible so you don't load up a single stab too much.

Yup that's what I'm planning to do, leave the oven circuit as is in case later on if I (or someone else) wants to install an electric stove top/oven, the option is there.

As for the stab limit, I'm not sure where to look for it. I do see that's there a text here saying that maximum sum of breaker rating per stab: 200A. That's probably fine with a quad (70a) and the ev (60a) on a same stab right? I'll double check with the installer tomorrow, thanks for the tip!

 

[Cosmacelf]

Under 2017 or later code, 6-6-6 or 6-6-8 copper type SE cable (type SEU or SER but NOT type USE) is another acceptable alternative. It is rated for 65A non-continuous or 52A continuous. This is new for type SE larger than #10 under 2017 and later codes - it was not allowed before.

Not the most common type of cable out there and the SEU in particular is a nuisance for homeowners to work with because you have to know how to neatly spin up the concentric ground strands for termination. But it is 75C rated and can be fished through walls/ceilings, which can save a lot of work running conduit sometimes.

4-4-6 aluminum SE cable is fine too, probably available at your local big-box store, and a lot cheaper than almost any other alternative, but at the charger end, requires an additional junction box, a few split-bolts or Polaris connectors, and a copper pigtail into the charger since modern Tesla chargers are not rated for use with aluminum wire.

Great find. In researching this I FINALLY found a good explanation why NM-B (and SE) cables had been derated to the 60 degree column. Click here to read it.

Anyways, you are right that in the 2017 NEC, they allowed 8 gauge or bigger cable to use the 75 degree column, meaning 6-6-8 SE cable has an ampacity of 65A. And even better the SEU variant cable can be used in wet or dry locations.

Home Depot has a good price on 6-6-8 SEU cable, comparable in price to 6-2 NM-B, but it only comes in 500' spools. If I were an electrician, I might use this instead of NM-B.

OR, I'd take a read of what I posted above and realize that the reason NM-B isn't allowed to use the 75 degree column is completely inapplicable to EVSE installs and just use 6/2 NM-B for 60A installs (yes, more heresy). I still like MC cable for 60 amp installs...

Edit, BTW what tls was referring to is the SEU cable construction is kinda wonky and you have to gather up the bare ground wire strands...

 

[Cosmacelf]

Yup that's what I'm planning to do, leave the oven circuit as is in case later on if I (or someone else) wants to install an electric stove top/oven, the option is there.

As for the stab limit, I'm not sure where to look for it. I do see that's there a text here saying that maximum sum of breaker rating per stab: 200A. That's probably fine with a quad (70a) and the ev (60a) on a same stab right? I'll double check with the installer tomorrow, thanks for the tip!

Yeah, I was being way too anal in that comment about stab limits. You're good no matter how the electrician does it there.

 

[Eric33432]

Yup that's what I'm planning to do, leave the oven circuit as is in case later on if I (or someone else) wants to install an electric stove top/oven, the option is there.

As for the stab limit, I'm not sure where to look for it. I do see that's there a text here saying that maximum sum of breaker rating per stab: 200A. That's probably fine with a quad (70a) and the ev (60a) on a same stab right? I'll double check with the installer tomorrow, thanks for the tip!

Yes, that text tells you each stab is limited to 200 amps. So you would want the total of the breakers on the left side and right side of any stab to be 200 amps or less.

You will be fine no matter how you consolidate to free up two positions to install a double pole breaker. That said, unless it would be easier to install the EVSE on a quad, which it might be in your case, I would still put the EVSE on a full size breaker, and consolidate four lesser loads onto either two 1 pole tandems or the dryer/oven on a 2 pole quad.

Great find. In researching this I FINALLY found a good explanation why NM-B (and SE) cables had been derated to the 60 degree column. Click here to read it.

Anyways, you are right that in the 2017 NEC, they allowed 8 gauge or bigger cable to use the 75 degree column, meaning 6-6-8 SE cable has an ampacity of 65A. And even better the SEU variant cable can be used in wet or dry locations.

Home Depot has a good price on 6-6-8 SEU cable, comparable in price to 6-2 NM-B, but it only comes in 500' spools. If I were an electrician, I might use this instead of NM-B.

OR, I'd take a read of what I posted above and realize that the reason NM-B isn't allowed to use the 75 degree column is completely inapplicable to EVSE installs and just use 6/2 NM-B for 60A installs (yes, more heresy). I still like MC cable for 60 amp installs...

Edit, BTW what tls was referring to is the SEU cable construction is kinda wonky and you have to gather up the bare ground wire strands...

View attachment 992527

That article is a great find. Might be why so many electricians use and inspectors allow the use of 6/2 NM on 60 amp EVSE circuits. I still would not advise someone to use it because you never know what an inspector might do.

 

[John in LB]

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

My recommendation is for your to go with option 1. In the extreme and unlikely event that you run all of your other breakers at full load, then the main breaker @ 125A will trip and protect you. So, I would not sweat it, (might be inconvenient or embarrassing, but not unsafe.) All of the other guys are just trying to sell you stuff...

If you are curious as to how much you are nominally pulling, turn on all of the devices that you would "normally" have on (that's not the same thing as having every single gadget on...) Pretend it's Thanksgiving, the oven is on and two guests are staying at your house... go out to your meter and read how many KWatts your pulling and divide that by your voltage to get a very good estimate of your "normal" high amperage draw. If this number is 50 Amps or less, then adding 48 amps for the car charger will be just fine.

Separately, I would oversize the wire used for this circuit, go one size bigger than what is called for in a 60 AMP breaker situation. The reason is energy efficiency: when your car is charging, it is pulling 48 amps for 1 to 5 hours continuously, this is very different than the amperage draw for your other appliances (intermittent, not every day, short duration). The price difference of the wire itself is nominal, but this circuit will be used for car charging for many years... hence the payout for avoiding the wasted energy due to voltage drop through the wire from the breaker panel to your car charger. (so even if electrician #1 says, it will cost you another $50-$100, it is worth it.)