Planning a *Boss system with a 400Amp service

[R1200GS]

I'm building a new house. The builder and electrician recommend going with a 400Amp service even if I don't need it because it costs a lot less to do it now. I'm not sure if I need it. I'm fine with a 200Amp now, but I have natural gas, the new home will be all electric. When adding every possible load I would exceed 200Amps, but does it ever happen?
Anyway, 400Amps will consist of 2 200Amps panels. I don't know yet if the electrician plans to put them side by side and add another subpanel or place the second panel closer to the high consumers in the kitchen and garage. This is a one story house, so it is spread up more than a two story.
How should I intergrate the Grid Boss into it? Dedicate one panel to the non backup loads and backup everything off the Grid Boss? Do I even need it in this setup? Maybe 18KPV is a better choice?
I tried to discuss it with ChatGPT. It repeatedly offered to produce a one wire diagram. The result was entertaining.

 

[DIYrich]

I would have the electrician install 2 gridboss in parallel before the split to the two 200a panels.

 

[Quattrohead]

I would have the electrician install 2 gridboss in parallel before the split to the two 200a panels.

You can't parallel grid bosses.

 

[Quattrohead]

Your plans should have an electrical load calculation, it will list the major appliances and an allowance for general use.
Share that with us please.

I built an all electric home in Florida and managed to keep it to less than 200a. I haven't pulled more than 80-90 amps from my dual 18kpv.

 

[mciholas]

Anyway, 400Amps will consist of 2 200Amps panels.

Separate the loads into A and B panels. A panels has the loads you want to run grid down, B has the loads you are okay with losing when grid is down. Put GB on panel A.

Examples of loads that could go on panel B: electric resistive heat, pool pump, dryer, stove, etc. You will find these loads tend to be large and not needed critically in a grid down situation, and everything else fits easily in 200 amps. You don't want to overload your inverters when the grid is down, so load shedding is best.

When grid is up, the inverters still power panel B before the meter, so you do use your power locally before it goes to the grid. This is important if you don't have 1 to 1 net metering.

Dedicate one panel to the non backup loads and backup everything off the Grid Boss?

Yes. You have to carefully figure out which loads to put in which panel. The lights and outlets don't add up to much, so put them all in panel A.

Do I even need it in this setup? Maybe 18KPV is a better choice?

GB really helps when you have two inverters as it avoids all the combiner panel crap. If you are sure you want only one inverter, then the 18Kpv could do it. Note that the GB also provides a bypass mode which you still should provide for the 18Kpv.

Mike C.

 

[Quattrohead]

I love the AI diagram, looks like it was on mushrooms at the time LOL

 

[R1200GS]

Thanks for your replies. I looked up a NEC load calculator online and with all the load adjustments applied I can't reach 200A even when adding a second EV charger and another power hungry appliance. I may still go with a 400Amps because it is a lot cheaper to do it at the build time.

 

[Quattrohead]

I still used 2 breaker panels anyway and it turns out I needed the room.
I did split critical and non-critical loads because at that time there was no grid boss. I now could use the 125A smart port to switch the non-critical panel on and off auto magically but I would have to do some rewiring.

 

[R1200GS]

As I understand it, GridBoss gives more granular control than just backup/non backup, although I think it has practical uses only when supported by a large battery. Otherwise, the emergency off grid consumption should be minimized.

 

[Brucey]

Thanks for your replies. I looked up a NEC load calculator online and with all the load adjustments applied I can't reach 200A even when adding a second EV charger and another power hungry appliance. I may still go with a 400Amps because it is a lot cheaper to do it at the build time.

From what I've seen 400A service sometimes comes into play when you only have heat pumps for heat and the temps plunge and the "emergency" strip heaters come on and start drawing an absolute shitton of power, while you've got the oven and couple elements on, water heater, clothes dryer etc. All those loads that would be covered by propane in you old place.

 

[R1200GS]

From what I've seen 400A service sometimes comes into play when you only have heat pumps for heat and the temps plunge and the "emergency" strip heaters come on and start drawing an absolute shitton of power, while you've got the oven and couple elements on, water heater, clothes dryer etc. All those loads that would be covered by propane in you old place.

According to this calculator https://ask-the-electrician.com/residential-electrical-load-calculation.html#beginAdv it is hard to exceed 200A unless the house is huge or it has some large additional loads like a heated pool. I'll have heat pump water heater and dryer, I replaced them with the regular ones in the calculator, added 2 car chargers and still couldn't get to 200A.

 

[Brucey]

According to this calculator https://ask-the-electrician.com/residential-electrical-load-calculation.html#beginAdv it is hard to exceed 200A unless the house is huge or it has some large additional loads like a heated pool. I'll have heat pump water heater and dryer, I replaced them with the regular ones in the calculator, added 2 car chargers and still couldn't get to 200A.
View attachment 276686

I don't know what its doing with derating in the calculation but seems like worst case it all adds up to 71kW?

 

[R1200GS]

This calculator is based on the NEC rules. Makes sense to me- it would be unusual to have everything running at full blast at the same time. If such event happens once in lifetime, it would be better to pop the breakers rather than overbuild.

 

[Quattrohead]

That's what I'm saying, it is very difficult to get to 200 amps with a somewhat regular home.
One bizarre thing my original calculations had was the each garage door opener was expected to pull 3.5 KW
There were several quite severe miscalculations throughout various plans for the home build that I had to correct the professionals on. The original heating cooling calculations called for 5ton and were revised to 2.5ton under my direction.

 

[Brucey]

Right, but let's take something that can happen day to day. Oven and stove are sucking up 10kW. Water heater going at 5kW. Hot tub at 7.5kW. Dryer at 5kW.

Heat pump with 15kW of resistance heaters.

Throw on a decent ev charger load like an f150 lightning extended at 11.5kW, and you are over a 200A supply of 48kW. That's not including any other general loads. So a 400A/dual 200A service seems to make sense, a second ev charger in the future seems likely.

As an all propane house for major loads I couldn't even approach 200A.

 

[R1200GS]

That's what I'm saying, it is very difficult to get to 200 amps with a somewhat regular home.
One bizarre thing my original calculations had was the each garage door opener was expected to pull 3.5 KW
There were several quite severe miscalculations throughout various plans for the home build that I had to correct the professionals on. The original heating cooling calculations called for 5ton and were revised to 2.5ton under my direction.

I agree, contractors often overestimate. A little bit more money for them and nobody will make angry calls that the house has too much power.
I hired someone to do Manual J for HVAC accounting for all details. Just going from 6 to 5 ton geothermal system saved me over $8k.