400A service upgrade, is it practical?

[DIYorBust]

I'm contemplating whether I could, or should undertake a service upgrade to 400A. I was pleased when I bought the home almost ten years ago now, to see that a previous owner had upgraded to 200A service, and installed NM-B in many areas of the home. However some circuits are still wired with the old-school BX cable without EGC. It appears compliant though, we've installed GFCIs where we needed 3-prong outlets. Still we chip away and replace when there is an opportunity.

Anyway, we are following the trend towards an electric house, and I'm wondering if I should upgrade the service, make some tradeoffs in my equipment plans, or maybe kick the can down the road. The home I'm guessing is about 2700 sq feet, with an attached garage, and a detached garage. I see you can get a pretty nice 200A panel like a square D QO load center for around 200-300 bucks, and cheaper options for less than 200 bucks, but 400A equipment seems to cost 10x that. Am I missing something there? Could I install a small 4 space 400A load center, and hook up to my current panel, and a second 200A panel as sub panels? And would I likely need to pay the utility to upgrade the transformer?

So right now I have these 240v loads which I think are continuous loads:
Pool pump MCA 20, 10-16A ammeter
Pool heat pump, MCA 43, 25 on the ammeter max(compressor start load not checked)


I'd like to add two 5 ton heat pumps, i'm guessing will pull about 32A each on a 40MCA. So now we're at 90+64 = 154. Now at some point I'd like to put in the following: electric dryer(30A), electric range(40A), EV charger or two(30-50A),

To summarize my guestimates:
Ordinary 120V loads = 60A(Lighting, appliances, electronics, tools, etc.)
Pool pump = <15A
Pool heat pump = 25A
Total: 40 + 30 if the panel is balanced = 70A

Desired loads(240V):
Two 5 ton heat pumps: 20x2 = 40A?
EV Charger: 40 AMPS
Range: 40A
Dryer: 30A
2nd EV Charger: 40A.
*Water heater: 30A
Additional Loads: ~220

So it seems like i could skip the dryer the range(currently propane), and the second EV charger, and get to 70+40+40=150. So maybe I could do one more appliance. I could see adding more loads down the road too, such as an electric water heater. So is there any chance it's worth upgrading the service, or should I try to stick to my 200A limitation, and maybe charge cars through a window near the dryer?

Thanks for your thoughts!

 

[Fitter30]

2700 sq ft doesn't need 10 tons of cooling. Contact your electric company ask if they offer a energy audit that includes a blower door test. With that information it will tell how tight the house is also the condition of windows ,doors and insulation in the ceiling. What sizes of equipment do you have now? How do they work for you?

 

[Sponsor]

 

[DIYorBust]

Right now we probably have a about 5 tons of cooling. We have a 240v 2200btu window unit, on the upper floor, the other has a ducted central system. The house is from 1920 and is not well sealed, although some improvements were made in the 80s. The extra capacity is not for cooling, but for heating. We currently have an oil fired steam system which works great, but it's not super efficient, and when the time comes to replace the boiler, or if oil prices go back up, I might stick with the heat pump. Plus there are larger incentives if you install a system that can heat the entire house in this state.

 

[bigb56]

The only real way to know what size service you need is by doing a load calculation https://iaeimagazine.org/2013/mayju...calculations-in-the-national-electrical-code/

If you find it close to a tipping point consider things like climate and number of people living there to help decide.

To answer your question about the 2-200 amp load centers yes you can do that, you would buy a 400 (320) amp meter base with double lugs on the load side and feed your 2 panels by back feeding their main circuit breakers. You can also go into separate disconnects then into MLO panels. You can go with whatever size panels you want, I've seen 400 amp services with a 200 and a 100, even saw one once with a 200 and a 60 just for the pool.

You are not missing anything on the cost, I retired in 2020 but at the time we could do 2 entire 200 amp services materials and labor for less than just the materials for a single 400.

I agree that 10 tons of cooling is high for 2700 square feet. We have 2500 and live in the Arizona desert and have one 5 ton and one 1.5 ton. How is your insulation? That can be a huge factor in equipment sizing as you probably already know. Ours isn't that great being a masonry build from 1952 with no interior fir outs so the only real insulation is in the attic.

edit: Just saw you are in NY so I'm guessing your heating load is greater than your cooling load.

 

[wwhitney]

Desired loads(240V):
Two 5 ton heat pumps: 20x2 = 40A?
EV Charger: 40 AMPS
Range: 40A
Dryer: 30A
2nd EV Charger: 40A.
*Water heater: 30A
Additional Loads: ~220

You need to learn how to do a load calculation per NEC Article 220. Start with the optional calculation in 220.82, the description is pretty short and not too hard to follow. Most of the loads will end up with a 40% factor applied to them, so your load calc may well come out to under 200A.

Cheers, Wayne

 

[DIYorBust]

The only real way to know what size service you need is by doing a load calculation https://iaeimagazine.org/2013/mayju...calculations-in-the-national-electrical-code/

Even with that you will have to consider things like how many people live there and your climate if you are close to a tipping point on the calcs.

To answer your question about the 2-200 amp load centers yes you can do that, you would buy a 400 (320) amp meter base with double lugs on the load side and feed your 2 panels by back feeding their main circuit breakers. You can also go into separate disconnects then into MLO panels. You can go with whatever size panels you want, I've seen 400 amp services with a 200 and a 100, even saw one once with a 200 and a 60 just for the pool.

You are not missing anything on the cost, I retired in 2020 but at the time we could do 2 entire 200 amp services materials and labor for less than just the materials for a single 400.

I agree that 10 tons of cooling is high for 2700 square feet. We have 2500 and live in the Arizona desert and have one 5 ton and one 1.5 ton. How is your insulation? That can be a huge factor in equipment sizing as you probably already know. Ours isn't that great being a masonry build from 1952 with no interior fir outs so the only real insulation is in the attic.

edit: Just saw you are in NY so I'm guessing your heating load is greater than your cooling load.

Let me take a shot(see below, rough estimate). The result doesn't surprise me a ton. Using the more generous method, the load is technically close to what the 200A panel can take, maybe dropping one or two appliances, or making some other changes it could get under 200, or maybe a 225 panel could be installed without changing the service. But realistically, if 2 evs are charging, the AC is running, the pool and heater are running, that is a pretty possible situation drawing 60+60+10+25 =155 amps. Now if you're cooking and drying laundry at the same time, not to mention lighting, small appliances, or water heaters, seems reasonably likely to trip the breaker. It's the EVs that get you I think. The less amps you give them, the longer they're on, and more likely stack with other appliances. I could live with one. It might be doable if I make some tradeoffs on the equipment, but I feel the breaker may trip occasionally, and there's really no room at all for additional loads such as shop or garden tools, although if the EV chargers are on outlets, it may be possible to plug them in there.

Is the move the squeeze as much in as possible, kick the can, and hope the price of 400A equipment comes down as more people buy EVs?

Existing Loads
	Quantity(units or sq feet)	Volt Amps(watts)	Total Volt Amps(watts)	notes
General Lighting	2900​	16200​	16200​	*not sure exact sq footage of house, 2900 likely close
Small appliance Branch Circuits	8​	1500​	12000​
Washing Machine	1​	1500​	1500​
Pool pump	1​	3840​	3840​
Pool heat	1​	7200​	7200​
Microwave @75%	1​	1500​	1500​
Dishwasher @75%	1​	1200​	1200​
Largest motor(pool heat pump)	1​	3840​	960​
Existing Loads	1​		44400​
Standard Method (3000+(16200-3000)*.35)+12000+1500+3840+7200+1500+1200+960			35820​
Standard Method Ampacity			149.25​
Optional Method(10000+(40740-10000)*.4)			23760​
Optional Method Ampacity			99​
Contemplated loads
Range	1​	8000​	8000​	*table 220 C
Dryer	1​	5000​	5000​
EV charger(30 amps only)	2​	7200​	14400​
Water Heater@75%	1​	4500​	4500​
Heat Pumps	2​	7200​	14400​
Contemplated Loads			46300​
Counting All Existing and Contemplated loads
Standard method(35820+46300)			82120​
Standard Method Ampacity			357​
Optional Method (23760 + 14400 + (8000+5000+14400+4500+)*.4)			50920​
Optional Method Ampacity			212​

 

[wwhitney]

Let me take a shot(see below, rough estimate).

In the optional method, you don't get to take a 75% reduction on appliances from 220.53; you just get to use the 40% factor. [Didn't check the calcs to see if you are doing that, but the presentations suggests you may be.]

Also, why do you have (8) SABCs? Those are only for the general purpose kitchen branch circuits. Any kitchen circuit for a specific appliance should be figured according to that appliance's nameplate.

On the EVSEs, if you want two, I'd suggest getting two that can communicate to jointly limit the charge rate to say 60A or 80A. I.e. it's occasionally nice to able to charge an EV at 60A, and it's occasionally nice to charge two EVs at once, but it's going to be less common that you wish you could charge two EVs at 60A each at once.

Is the move the squeeze as much in as possible, kick the can, and hope the price of 400A equipment comes down as more people buy EVs?

With the exception of multiple EVSEs, even the optional method in 220.82 is likely conservative. So I recommend sharpening the load calc as much as possible and staying under 200A. And then I expect your non-EVSE usage will never exceed 100A.

Speaking of which, as part of the first phase of expansion, you can install a whole house logging meter to record your usage (binned into 15 - 60 minute bins). Then after you have a year of data, you can apply 220.87, which is fairly realistic. That should allow you to actually load up your service to get a real world current approaching 200A.

Cheers, Wayne

 

[Fitter30]

Right now we probably have a about 5 tons of cooling. We have a 240v 2200btu window unit, on the upper floor, the other has a ducted central system. The house is from 1920 and is not well sealed, although some improvements were made in the 80s. The extra capacity is not for cooling, but for heating. We currently have an oil fired steam system which works great, but it's not super efficient, and when the time comes to replace the boiler, or if oil prices go back up, I might stick with the heat pump. Plus there are larger incentives if you install a system that can heat the entire house in this state.

Over sizing cooling isn't a good idea. Unit will short cycle, RH will be high and duct work will be to small. House won't feel comfortable at all. Good windows and doors mean a lot.

 

[DIYorBust]

Over sizing cooling isn't a good idea. Unit will short cycle, RH will be high and duct work will be to small. House won't feel comfortable at all. Good windows and doors mean a lot.

It's my understanding that the heat pumps can down modulate From a practical perspective, in NY the heating load will be much larger than the cooling load, and I believe the heat pump systems commonly installed are designed to account for this, and can reduce the compressor speed based on the load. The windows are mostly Andersen replacement windows, there is room to upgrade the building envelope for sure, but much of the low hanging fruit has been taken. I may take your advice and have an engineer or a BPI inspector do an inspection, I think the utility co will pay. Thanks!

 

[DIYorBust]

In the optional method, you don't get to take a 75% reduction on appliances from 220.53; you just get to use the 40% factor. [Didn't check the calcs to see if you are doing that, but the presentations suggests you may be.]

Also, why do you have (8) SABCs? Those are only for the general purpose kitchen branch circuits. Any kitchen circuit for a specific appliance should be figured according to that appliance's nameplate.

On the EVSEs, if you want two, I'd suggest getting two that can communicate to jointly limit the charge rate to say 60A or 80A. I.e. it's occasionally nice to able to charge an EV at 60A, and it's occasionally nice to charge two EVs at once, but it's going to be less common that you wish you could charge two EVs at 60A each at once.


With the exception of multiple EVSEs, even the optional method in 220.82 is likely conservative. So I recommend sharpening the load calc as much as possible and staying under 200A. And then I expect your non-EVSE usage will never exceed 100A.

Speaking of which, as part of the first phase of expansion, you can install a whole house logging meter to record your usage (binned into 15 - 60 minute bins). Then after you have a year of data, you can apply 220.87, which is fairly realistic. That should allow you to actually load up your service to get a real world current approaching 200A.

Cheers, Wayne

Thanks Wayne, you're right I double counted the demand reduction in the optional method, missed that. The 8 SABCs, I wasn't sure what to count since I have other circuits where we use things like garden tools, bench grinders, etc. I don't think it changes the story much.

I think your insight is correct. we can manage the use of the distribution system, particularly as it pertains to the EV usage. I'm aware of one charger that will operate off a single supply, and charge two EVs at once, albeit at half the current. However my goal was to have EV charging at two different locations. Nonetheless, it would be easy enough to refrain from charging two EVs when cooking and drying on a hot day, I think you can typically program them to charge overnight. Unfortunately the design of these systems doesn't really allow automatic turndown of chargers when demand is high. But if I needed two cars ready to go in 4 hours, might have to turn of some other equipment. One issue is whether an electrician will agree with the load calc, but often they don't even bother unless there's a service upgrade. Thanks, it sounds like it's workable.

 

[wwhitney]

Unfortunately the design of these systems doesn't really allow automatic turndown of chargers when demand is high.

There are a few that do dynamic load management, see https://www.reddit.com/r/evcharging/wiki/load_management/ The J1772 protocol allows the EVSE to adjust the maximum allowable charge rate during the session, so the EV is supposed to reduce its charge rate accordingly.

Cheers, Wayne

 

[bigb56]

You count equipment that is fastened in place. Your general use receptacles are included in your lighting load. In residential, general use wall plugs are not included like they are in commercial/industrial.

The SABC requirement is kind of controversial, you are required to have at least 2 but if you install more than 2 then you have to count them. What's silly about that is often we install additional SABCs just to spread out the load, for instance we will add a separate one for the dining room but it will never get used for a small appliance, still we have to count it. If we had just left the dining room on the kitchen SABC (which is totally legal) we wouldn't have to count an extra 1500 VA. Same goes for the fridge, leave it on the kitchen SABC)(again legal) and it doesn't get counted in the load calc but run a separate circuit now you have to add another 1500.

 

[DIYorBust]

There are a few that do dynamic load management, see https://www.reddit.com/r/evcharging/wiki/load_management/ The J1772 protocol allows the EVSE to adjust the maximum allowable charge rate during the session, so the EV is supposed to reduce its charge rate accordingly.

Cheers, Wayne

Wow super helpful. I had no idea this was possible. I was looking to replace my emporia VUE that died anyway, if I bundle with this I might get exactly what I'm looking for without doing a very expensive service upgrade. Thanks Wayne, and thanks to the forum.

 

[DIYorBust]

You count equipment that is fastened in place. Your general use receptacles are included in your lighting load. In residential, general use wall plugs are not included like they are in commercial/industrial.

The SABC requirement is kind of controversial, you are required to have at least 2 but if you install more than 2 then you have to count them. What's silly about that is often we install additional SABCs just to spread out the load, for instance we will add a separate one for the dining room but it will never get used for a small appliance, still we have to count it. If we had just left the dining room on the kitchen SABC (which is totally legal) we wouldn't have to count an extra 1500 VA. Same goes for the fridge, leave it on the kitchen SABC)(again legal) and it doesn't get counted in the load calc but run a separate circuit now you have to add another 1500.

Thanks Bigb, yes I think I understand what you are saying. It would seem better, from a practical perspective to have more SABCs to avoid tripping the branch circuit breaker, but too many SABCs could risk increasing the service load calculation. It sure seems better not to have your fridge shut off if something else trips the GFCI or breaker, but that may be a tradeoff if you are near the panel max. Thanks a lot for the advice.

 

[wwhitney]

Same goes for the fridge, leave it on the kitchen SABC)(again legal) and it doesn't get counted in the load calc but run a separate circuit now you have to add another 1500.

If the fridge is on its own circuit, you can use its nameplate rating rather than the 1500 VA required for an SABC.

Cheers, Wayne

 

[bigb56]

Thanks Bigb, yes I think I understand what you are saying. It would seem better, from a practical perspective to have more SABCs to avoid tripping the branch circuit breaker, but too many SABCs could risk increasing the service load calculation. It sure seems better not to have your fridge shut off if something else trips the GFCI or breaker, but that may be a tradeoff if you are near the panel max. Thanks a lot for the advice.

The number of circuits doesn't necessarily change the load, even though it changes the load calculation. Being that you live there you know your usage and if your usage on 4 SABCs is the same as it would be on 2 then figure 2. I never had an inspector in the field question a load calculation, that was all done on paper down at city hall.

 

[DIYorBust]

The number of circuits doesn't necessarily change the load, even though it changes the load calculation. Being that you live there you know your usage and if your usage on 4 SABCs is the same as it would be on 2 then figure 2. I never had an inspector in the field question a load calculation, that was all done on paper down at city hall.

Makes sense, if you run a countertop microwave and an electric kettle at the same time on the same breaker you will trip it, but both will usually have a short runtime, unlikely you would trip the main breaker if you ran them on two different circuits.