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Just as a practical thought, if you’re running electricity to the detached garage anyway, I would think it would be nice to have a 120V circuit for regular outlets and an overhead light. So I was thinking maybe run 80A over there, and then split it to 50A for the HPWC (or 14-50 outlet) and then 20A for the 120V lighting and outlets.
 
You may not need to put in a sub-panel in the garage, if you have available space on you panel in the house for an extra 50A breaker.
Of course, you would then have to run a line/conduit from you main panel to the garage. That's what I had done. And the house in which this was done had electric heat and hot water heater.

Talk to you electrician about the cost of running the line. Unless the garage is very far from the house, it has to be a lot less expensive than the new transformer.

A quick point for those who may read this later: if this garage is detached, then you will require a a subpanel for anything more than a single circuit. Based upon the conversation in this specific thread, though, I assume it's attached and in that case you can do "home run" circuits from the main panel if breaker space is available. If the building is detached, however, no more than one circuit (2-wire or MWBC) or feeder can span between buildings.

The benefit of a subpanel is that if you plan to have two EV's, and plan to stagger charging times such that the two-plus cars wouldn't be charging at the same time, you eliminate a lot of wire cost by running a feeder instead of multiple individual circuits.
 
A quick point for those who may read this later: if this garage is detached, then you will require a a subpanel for anything more than a single circuit. Based upon the conversation in this specific thread, though, I assume it's attached and in that case you can do "home run" circuits from the main panel if breaker space is available. If the building is detached, however, no more than one circuit (2-wire or MWBC) or feeder can span between buildings.

The benefit of a subpanel is that if you plan to have two EV's, and plan to stagger charging times such that the two-plus cars wouldn't be charging at the same time, you eliminate a lot of wire cost by running a feeder instead of multiple individual circuits.
I definitely need a subpanel in the garage and I will be installing one.
 
Would 25kVA necessarily be undersized for six houses if everyone's using gas appliances? I count 8 homes (and a small church!) on my 25kVA transformer and I've had no trouble even on summer afternoons with everyone's AC running. We're all on gas, though; if we were all using electric heating I can see that being woefully undersized...
 
Would 25kVA necessarily be undersized for six houses if everyone's using gas appliances? I count 8 homes (and a small church!) on my 25kVA transformer and I've had no trouble even on summer afternoons with everyone's AC running. We're all on gas, though; if we were all using electric heating I can see that being woefully undersized...
The power company doesn't seem to think it's a problem. I guess if the voltage drops too much people will complain and they'll upgrade it.
Anyway, the electrician, building inspector and power company are happy with me having just 200 amp service so that hurdle is over.
 
I am casting a resurrection spell on this thread because I am having the same question.

I have a 3300 square foot home that was built in 2004 with 200 amp service. Most of these "McMansions" being built now are specced out with 400 amp service from the utility so that the owners don't have any concerns about running their finished basements, hot tubs, etc.

Right now I don't have anything installed aftermarket, this is the first service addition I'm doing other than installation of a 7000 watt PV system about 5 years ago.

I have a 50 amp breaker for my AC, 40 amp breaker for electric dryer, 50 amp breaker for double oven, 50 amp breaker for cooktop (which is gas, go figure), 30 amp breaker for gas furnace, and a 50 amp sub-panel that runs all of the interior outlets and lighting.

I'm planning on doing my own installation of a 60 amp breaker that will run 6/3 Romex about 35 feet to a Tesla wall connector in an attached garage to power a Model 3 I am getting later this year.

However, I'm not wanting to do this if the inspector is going to show up and fail me because I'm over-subscribed on service.

How hard is it to get most utility companies to do a load study?
 
I am casting a resurrection spell on this thread because I am having the same question.

I have a 3300 square foot home that was built in 2004 with 200 amp service. Most of these "McMansions" being built now are specced out with 400 amp service from the utility so that the owners don't have any concerns about running their finished basements, hot tubs, etc.

Right now I don't have anything installed aftermarket, this is the first service addition I'm doing other than installation of a 7000 watt PV system about 5 years ago.

I have a 50 amp breaker for my AC, 40 amp breaker for electric dryer, 50 amp breaker for double oven, 50 amp breaker for cooktop (which is gas, go figure), 30 amp breaker for gas furnace, and a 50 amp sub-panel that runs all of the interior outlets and lighting.

I'm planning on doing my own installation of a 60 amp breaker that will run 6/3 Romex about 35 feet to a Tesla wall connector in an attached garage to power a Model 3 I am getting later this year.

However, I'm not wanting to do this if the inspector is going to show up and fail me because I'm over-subscribed on service.

How hard is it to get most utility companies to do a load study?

If your cooktop is gas, then I don't think you'd have to figure that out in the calculations at all. Some houses have dual fuel setups that do gas+electric for ranges so that might be why you have a 50 amp breaker for the cooktop. One of my dogs figured out how to turn on the gas burners on my gas range. When I pulled out the gas range, I was pleasantly surprised to find the unused 50 amp outlet. It allowed me to easily change from gas to induction.

Also, I doubt you'd be using your AC and the gas furnace at the same time so they'd probably only need to include the larger one (AC) in any load calculations. Since the WC allows you to set different values, I think you could easily install it with a 60 amp breaker to handle 48 amps continuous load. In my house, we have 200 amps to the house and were able to run 100 amps to the subpanel in the garage. We split that into a couple 14-50 outlets but will be upgrading to the load-balanced WCs this year (which didn't exist when we got the 14-50 outlets installed).
 
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I am casting a resurrection spell on this thread because I am having the same question.

I have a 3300 square foot home that was built in 2004 with 200 amp service. Most of these "McMansions" being built now are specced out with 400 amp service from the utility so that the owners don't have any concerns about running their finished basements, hot tubs, etc.

Right now I don't have anything installed aftermarket, this is the first service addition I'm doing other than installation of a 7000 watt PV system about 5 years ago.

I have a 50 amp breaker for my AC, 40 amp breaker for electric dryer, 50 amp breaker for double oven, 50 amp breaker for cooktop (which is gas, go figure), 30 amp breaker for gas furnace, and a 50 amp sub-panel that runs all of the interior outlets and lighting.

I'm planning on doing my own installation of a 60 amp breaker that will run 6/3 Romex about 35 feet to a Tesla wall connector in an attached garage to power a Model 3 I am getting later this year.

However, I'm not wanting to do this if the inspector is going to show up and fail me because I'm over-subscribed on service.

How hard is it to get most utility companies to do a load study?


You can do it yourself. Most difficult thing is getting the rated power usage for the appliances (should be on a label). The breaker size is not the determining factor.
Here is one site that does the math for you,
6 Gauge NM-B is rated for 55 Amps, since those breakers don't always exist, you can round up to 60, but a 50 would be a more conservative choice, especially with the HPWC set to a 50A breaker (40 amp draw). Having the HPWC set for a 60A breaker would draw 48A. It sounds like your cooktop is not fused correctly. Guessing it was set up for electric originally, might be good to down size the breaker to match the unit (likely specifies a smaller breaker). You might be able to use the 50 for the new connection and put a right sized breaker in for the cooktop.

Referring to @MorrisonHiker comment. The furnace load is mostly the blower which is used during AC operation, but the breaker is sized for the starting load of the blower (compressor and fan for the AC unit), that is why you need the nameplate ratings.
 
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Update.
Today had the electrician and building inspector both here at the same time.
I didn't want to confront the electrician and tell him he was wrong so I asked the building inspector "How can we do this?".
His answer was that we can, indeed, have 200 amp service with two 200 amp panels, each connected with it's own breaker.
The load calcs I did show that I'm well within 200 amps (100 + 84 demand load) for both buildings so 200 amp service should be fine.

Everybody is happy now.

Power company is coming tomorrow and I'll talk to them about the 25 kW transformer serving eight customers.

In case you haven't updated your service yet. I used feed through mobile home panels for my service entrance. It has the 200A main breaker and pass through lugs to go to your original panel (which will need grounds and neutrals separated). You can then add a 100A breaker for the garage subpanel. An additional nice feature is that you can get a manual mechanical interlock kit to allow connection of a generator which will then supply both the house and garage. PW0816B1200TC is the one I have.
 
You can do it yourself. Most difficult thing is getting the rated power usage for the appliances (should be on a label). The breaker size is not the determining factor.
Here is one site that does the math for you,
6 Gauge NM-B is rated for 55 Amps, since those breakers don't always exist, you can round up to 60, but a 50 would be a more conservative choice, especially with the HPWC set to a 50A breaker (40 amp draw). Having the HPWC set for a 60A breaker would draw 48A. It sounds like your cooktop is not fused correctly. Guessing it was set up for electric originally, might be good to down size the breaker to match the unit (likely specifies a smaller breaker). You might be able to use the 50 for the new connection and put a right sized breaker in for the cooktop.

Referring to @MorrisonHiker comment. The furnace load is mostly the blower which is used during AC operation, but the breaker is sized for the starting load of the blower (compressor and fan for the AC unit), that is why you need the nameplate ratings.

I don't see anything on the permit request that specifies this. Is this just what I would want to do to make sure I'm "safe" with the install I want to do?

Now that I look at it the 50 amp breaker for the gas cooktop also has a note that it runs the 1800 watt microwave, so I guess that might be a partial explanation on that one but have never seen a microwave pull those kind of amps before.

As you noted too, my furnace blower has to operate when running the AC... the startup load on that is nearly 20 amps all by itself but once it's up and going it settles down to about 6 amps.

I just don't want to be in a situation where my wife is cooking Thanksgiving dinner using both electric ovens, drying clothes, furnace is on and then charging the car starts popping fuses... I'll never hear the end of it.

I was going to put a 60A circuit in since the Model 3 LR is confirmed to have 48A charging from the wall charger... would get the most bang for my buck that way and if needed I could always change the wall charger to only charge it at 32A if 48A was too much.
 
I don't see anything on the permit request that specifies this. Is this just what I would want to do to make sure I'm "safe" with the install I want to do?
Inspector might want to see the load calc.

Now that I look at it the 50 amp breaker for the gas cooktop also has a note that it runs the 1800 watt microwave, so I guess that might be a partial explanation on that one but have never seen a microwave pull those kind of amps before.
I'm guessing the original 50A 240V feed for an induction or other electric cook top was turned into 2 120V circuits with a shared neutral (commonly done with dishwasher and disposal). The breaker could then possibly change to a dual pole 20A, but it is best to check the connections. Is it an over the cook top microwave?

As you noted too, my furnace blower has to operate when running the AC... the startup load on that is nearly 20 amps all by itself but once it's up and going it settles down to about 6 amps. I just don't want to be in a situation where my wife is cooking Thanksgiving dinner using both electric ovens, drying clothes, furnace is on and then charging the car starts popping fuses... I'll never hear the end of it.
At least in the northern hemisphere, the AC won't be on too. :)
This is where the load calc helps.
48 (car) 40 (dual ovens) 5(furnace) 30 (dryer) 20 (lights) = 143 Amps. well under the continuous rating of 160A (breaker should be 125% of continuous + 100% intermittent).

I was going to put a 60A circuit in since the Model 3 LR is confirmed to have 48A charging from the wall charger... would get the most bang for my buck that way and if needed I could always change the wall charger to only charge it at 32A if 48A was too much.
That likely works since the cable is good for 55A and the HPWC won't go over 48A.
 
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Inspector might want to see the load calc.


I'm guessing the original 50A 240V feed for an induction or other electric cook top was turned into 2 120V circuits with a shared neutral (commonly done with dishwasher and disposal). The breaker could then possibly change to a dual pole 20A, but it is best to check the connections. Is it an over the cook top microwave?


At least in the northern hemisphere, the AC won't be on too. :)
This is where the load calc helps.
48 (car) 40 (dual ovens) 5(furnace) 30 (dryer) 20 (lights) = 143 Amps. well under the continuous rating of 160A (breaker should be 125% of continuous + 100% intermittent).


That likely works since the cable is good for 55A and the HPWC won't go over 48A.

Thanks for all your replies I appreciate it.

Yes, the microwave is one of those fancy over the cooktop deals. This model home came standard with an electric cooktop and an upgrade option from the builder to gas. Since my home was a "spec home" where I didn't choose any of the options it's possible that it started out with the intent of being electric and was wired for that and then they converted it when they realized they would have to pick the options that would be most likely to sell the place.

It worked too, I bought the home partially because it had the "gourmet kitchen" upgrades... electric cooktops suck. :)

I'm going to have to get the ratings on everything because in the example you posted of being under load while cooking thanksgiving dinner, I would be OVER load if doing all the same things but instead of running the furnace I was running my monster AC unit.... depending on how much relief my solar PV was providing at the time.
 
Thanks for all your replies I appreciate it.

Yes, the microwave is one of those fancy over the cooktop deals. This model home came standard with an electric cooktop and an upgrade option from the builder to gas. Since my home was a "spec home" where I didn't choose any of the options it's possible that it started out with the intent of being electric and was wired for that and then they converted it when they realized they would have to pick the options that would be most likely to sell the place.

It worked too, I bought the home partially because it had the "gourmet kitchen" upgrades... electric cooktops suck. :)

I'm going to have to get the ratings on everything because in the example you posted of being under load while cooking thanksgiving dinner, I would be OVER load if doing all the same things but instead of running the furnace I was running my monster AC unit.... depending on how much relief my solar PV was providing at the time.

Running AC was only 6 amps I thought. Don't be as concerned with the starting current.
My spec house was dual source for dryer and stove too.
 
Electric does but have you given induction a try? You can boil water in seconds and the cooktop stays cool. Amazingly safe compared to gas or electric and way more efficient.

I've played around with friends induction cooktops. While I'm not a gourmet chef, I can cook and have taken cooking classes. There's a reason that every professional kitchen is well stocked with gas burners. ;)
 
Running AC was only 6 amps I thought. Don't be as concerned with the starting current.
My spec house was dual source for dryer and stove too.

The blower for the furnace uses about 20 amps when starting whether it's driving the AC or the furnace forced air system.

The AC itself is on a 50 amp breaker all by it's lonesome and is a super inefficient 8 SEER unit that I'm not quite ready to get rid of. I'm sure that monstrous hog pulls 30+ amps when starting up.
 
@voip-ninja I'm far more oversubscribed than you, but had no concerns from the electricians or the building inspector. I just added a 50a breaker & HPWC. Was going to add 100a, but I was able to get unlimited off-hours charging for $30/mo if I keep it under 40a. They didn't think there was a problem with 100A either...

I have 200a main panel. 4600 sq ft house. 3 HVAC (propane heat), propane hot water, 2 electric ovens, microwave, fridge, electric dryer.

Most of the lighting has been converted to LED.
 
The blower for the furnace uses about 20 amps when starting whether it's driving the AC or the furnace forced air system.

The AC itself is on a 50 amp breaker all by it's lonesome and is a super inefficient 8 SEER unit that I'm not quite ready to get rid of. I'm sure that monstrous hog pulls 30+ amps when starting up.
Starting load isn't an issue (usually). You can pull all 200 rated amps when needed (motor starts can exceed that).
But real numbers will tell the tale.
 
I've played around with friends induction cooktops. While I'm not a gourmet chef, I can cook and have taken cooking classes. There's a reason that every professional kitchen is well stocked with gas burners. ;)
And most garages have gas cars in them but that doesn't mean they are better. More and more gourmet home kitchens are installed with induction these days. The chef in my household went to culinary school (and got a degree) and prefers induction. Just like electric cars, we won't ever consider switching back to gas.
 
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