Hi forum.
I am new, and I am an architect working mostly residential.
I currently having a house with 200A main panel (with metter). We try to add another sub panel 125A for the house new addition (1000sf).

My knowledge of electrical work limits to fill out the panel schedule with amperage and VA in computer program. For this house the current 200A panel estimate connected load is 187A and the proposed 125A is 103A estimated load.
Q: do I need a 325A Disconnect (after the metter, and upstream from 200A and 125A panels) ?
Or will it just be ok if electrician can parallelly hot wired the subpanel feed to the 200A panel (if he chooses to) ?

The boldest wire inside this 200A are only #4 awg. My kindergarten electrical knowledge tells me I would need a #350 wire (after the metter) to make sure nothing blows up, but that thought can be seriously wrong
Let me know, please

 

If a qualified electrician is involved, as you indicate, then he should know and be able to advise you. Methods can vary according to jurisdiction.
You also need to know if the supply company's service is adequately sized already for the addition..

 

Do you really think you house will pull 325A? (187 + 103=)
What addition will need 124? Do you have a second oven in the addition?
How do you get to 187 amps? Stove + dryer + oven + hot tub + AC + lights + computers =
electric heat?

Add up all the sub breakers. This number can exceed the 200A main breaker. There is an assumption that most breakers are not run close to the max. Most people by now have replaced their 100W and 60W lights for 6 and 3 watt bulbs. I don't even count light now days.

 

If a qualified electrician is involved, as you indicate, then he should know and be able to advise you. Methods can vary according to jurisdiction.
You also need to know if the supply company's service is adequately sized already for the addition..

Thank you, at this point in time the electrician is not in the vicinity just yet. I however would like to show information in the plans for city planchecker.
I can simply put down "work to be design/performed by license electrician" and be done with it, but that will put a stop to my learning.

 

First I suggest you give this a read, Best Practices for Electrical Sub-Panel Installation. Next I question when you say:

For this house the current 200A panel estimate connected load is 187A and the proposed 125A is 103A estimated load.

A 200 amp panel with a constant current draw of 187 amps makes no sense, that is a very large current draw as is 103 amps on a 125 amp sub panel. My suggestion would be a licensed qualified and bonded electrician to do all the work.

Ron

 

Do you really think you house will pull 325A? (187 + 103=)
What addition will need 124? Do you have a second oven in the addition?
How do you get to 187 amps? Stove + dryer + oven + hot tub + AC + lights + computers =
electric heat?

Add up all the sub breakers. This number can exceed the 200A main breaker. There is an assumption that most breakers are not run close to the max. Most people by now have replaced their 100W and 60W lights for 6 and 3 watt bulbs. I don't even count light now days.

Thanks, these are the panel schedules.
The house has car chargers.
The addition will have AC.

 

I had not thought about two car chargers.
-The 120V car chargers draw 15 to 20A
-The 220V car chargers draw 15, 32 or 50A depending on conditions, what car. etc.
When I weld, we turn off the close dryer, and you may have to unplug the cars.

A 200A service probably has a 2/0 copper or 4/0 aluminum wire to the meter. If you want to add another 100A in parallel, that is above my paygrade. Adding a subpanel is easy for me. You might need all new wire and that is a big project. Maybe a new meter.

 

I suggest that you have two properly sized disconnect switches, possibly fused disconnects so that the breaker panels may be conveniently located, rather than close to the meter.entry point.
ALSO, I have done electrical work in a house that had several 200 amp breaker panels with about 40 breakers in each. Not a budget dwelling by any means. The purchase price had been $4.24 million. Enough to buy the whole neighborhood I live in.

 

I had not thought about two car chargers.
-The 120V car chargers draw 15 to 20A
-The 220V car chargers draw 15, 32 or 50A depending on conditions, what car. etc.
When I weld, we turn off the close dryer, and you may have to unplug the cars.

A 200A service probably has a 2/0 copper or 4/0 aluminum wire to the meter. If you want to add another 100A in parallel, that is above my paygrade. Adding a subpanel is easy for me. You might need all new wire and that is a big project. Maybe a new meter.

+1 on a seperate meter if you have the budget for the up-front costs. Those EV loads will likely limit normal house activities. The second meter can have in places like CA (tiered electrical billing), off-peak billing plan costs half that of normal house loads.
http://www.evelectricity.com/evmeters/install.php

 

One problem to consider is the line feed into the building. If the building has 200 Amp service then the feeder is for 200 amp service and 200 amps is as good as it gets. Now if you want 240 volt 300 amp service that is a new can of worms. You can't exceed whatever the service entry is. This is why previously suggested a competent qualified electrician who knows and understands the NEC in addition to any local or state codes which may apply. Adding 100 amp service is not as simple as daisy chaining a 100 amp service panel.

Ron

 

My friends charge at 20A. I think they tell the car how much to pull but I don't know.
From day-1 car charging was intended to happen after people went to bed, and the AC is not working as hard.

 

This discussion makes me wonder what folks who create these mandates are thinking about when they tout the wonderfulness of electric vehicles. Wit the present grid already running at close to max, and the panic mode rush to somehow double the generating capacity, where is the power for the 100% electric fleet going to come from???
It is often wise to consider the secondary results of ones actions before acting.

 

From day-1 car charging was intended to happen after people went to bed, and the AC is not working as hard.

Although that was the intention to expect it to actually happen is a huge mistake on their part. People are going to charge when it's convenient to them... not when the manufacturers intended it to happen.

 

The timing makes little difference if everybody sets the timer to start charging at midnight.
I fully anticipate that all the folks who can charge at home will CHARGE AT HOME, because of both the inconvenient time for the more expensive fast charge to happen AND the reduction in battery life due to that fast charge.
YES!!, A Fast Charge does stress the battery and it does reduce the battery life a bit. Certainly this is a topic never brought up outside of the very technical publications. So who would want to buy a used car when the needed battery replacement will be at least $5000? Battery life is the other topic very seldom mentioned in any serious detail, because it is not a happy topic. Of course, it only applies to those folks who keep their cars longer than four years. And not one single politician cares about those folks.

 

The power companies are moving to a system where the cost of power depends on time of use. The grid must hold up in the hot afternoons and evenings, but power is mostly not used at 2am. Some heavy manufacturing plants have moved the "work day" to off peak times and they get a large cut in the power bill.

In some areas where there is not enough power to go around, the power company. offers a cut in price if they can talk to your AC unite. On high demands days they will shut off the AC for 10 minutes at a time to save peak power. It is better to have you AC power interrupted for 10/60 minutes than to have the grid fail and millions of people have no power for hours. Many car chargers are smart and can talk to the power company. They have the option to charge slow or not at all during peak demand. By pushing off the car charging time to non-peak times the grid is much more stable. Cost of understructure is less.

 

Some decades ago, residences in the UK installed off-peak (after midnight) storage heaters, these were fed by a separate meter, and were charged at a lower rate.
If the amount of rooms/heaters was large, the service Co. would bring 3phase in for them.
.

 

Home and public charging are both a mess in the fossil to all electric transition. For the grid, there will be no slack/non-peak time much like there is no slack-time for traffic in LA today

The infrastructure to support it is just missing.

 

Make sure your electrician does the job right. There's a lot of power flowing for long periods of time (high power and duty cycle operation that most home electrical systems are not designed for by default even on new houses).
All of the connections MUST be sized and installed correctly.

 

OK, so if everybody with an EV decides to charge at the lower price time starting at 1 AM, all that does is push the overload time to the middle of the night. My point being that the grid as it presently exists is not able to support that many charging EVs at any time. THIS is what the fools never consider, and never ever mention in public discussions.
In addition, every bit of that electrical power used to charge those batteries must be generated somewhere by some sort of system. So what is going to produce all of that electrical power?? And what sort of energy source will be used to produce it?? Solar power does not arrive at night, and the wind does not always blow when wanted. And a lot of folks are horribly afraid of atomic power plants.

 

OK, so if everybody with an EV decides to charge at the lower price time starting at 1 AM, all that does is push the overload time to the middle of the night. My point being that the grid as it presently exists is not able to support that many charging EVs at any time. THIS is what the fools never consider, and never ever mention in public discussions.
In addition, every bit of that electrical power used to charge those batteries must be generated somewhere by some sort of system. So what is going to produce all of that electrical power?? And what sort of energy source will be used to produce it?? Solar power does not arrive at night, and the wind does not always blow when wanted. And a lot of folks are horribly afraid of atomic power plants.

Just use your super-human powered generator to make the extra power for EVs.