400 amp residential question

[Copperclad]

Hi everyone!
Im looking at a set of prints for a very large residence & detached garage.
On the one line, they show a 400 amp 1 phase service, which is fine. What has me bothered, is the fact they show (3) 200 amp load centers feeding off the main 400 amp gear. (1) 200a panel in garage, (1) 200a panel in the main house first floor, and (1) 200a panel in the main house second floor.
The load calculation came out to 78kva. which is fine for a 400 service , it just does not seem right to pull a potential 600 amps from a 400 amp service.
I have never bid on a residential job this big it may very well be the norm, I would much appreciate some input from some of you experts.

Thanks guys!

 

[david]

The service conductors have to be sized to carry the total max calculated load.
As far as how you distribute the load you could have as many 200 amp (feeders) sub-panels as you desired.

 

[augie47]

With the 78kva load calculation, you are obviously fine with the 400 amp service, however, you might want to make sure the load is divided in a such a way not to overload any one panel.
(What you have is not much different than (20) 20 amp breakers in a 200 amp MB Panel)

 

[petersonra]

are these feeders going to have OCP? or are they taps to the 3 panels?

 

[RLyons]

With the 78kva load calculation, you are obviously fine with the 400 amp service, however, you might want to make sure the load is divided in a such a way not to overload any one panel.
(What you have is not much different than (20) 20 amp breakers in a 200 amp MB Panel)

There is still a 200a MB protecting the service conductors.
I've seen 7 - 200a MB with panels on a 400 Amp service...no 400A breaker so without proper calcs people could just keep adding circuits to panels assuming as long as they don't go over 200 they are ok? Another question I have is when running parallels what happens if you loose a conductor?

 

[electrofelon]

probably will never see over a hundred amps on that service unless they are growing marijuana

 

[Robert Whiteaker]

It's all about actual load.

It's all about actual load.

I have been in San Francisco for many years and I have seen 28 studio units run off of a 150 amp single phase service no problem. If it's residential load and the main heating for the home, water heater and clothes dryer etc are gas powered it is a rare situation where the whole house will ever actually use even 100 amps. Load calculations are meant to give you enough power for each individual circuit. In a residence the likelihood of every single circuit whether they are circuits that serve panels or circuits that serve appliances and utilities all being used to their absolute max is almost impossible.

Obviously if you are designing a panel that is in a business that operates all day you can load it up with the max of 80%. But people in a home even at Thanksgiving running their ovens charging their electric vehicle drying their clothes and swimming in their hot tub rarely come close to their 80% if the contractor gave them the proper size service. As was said earlier you could put a series of 200 amp panels in as long as the total load is 80% of the total load allowed by the main and in this case that would be 320 amps. I have never seen a home under 10K square feet come close to that.

Best of luck and I hope you make money!

 

[jcassity]

in my opinion only i think the better term would been "its close" on your load calcs.

reason i say this is this...
Observe the UT entrance size and meter base pn deployed or in place by the UT co. They might actually only deliver to you 320A service.

with the magnitued of sub panels your speaking to, its a good idea to maximize the room for room redundancy on circuits.

I personally would design each room with 50% outlets and 50% lights on dedicated circuits.
meaning a basic bedroom would have 2 sources for lights and 2 sources for outlets.
When your asked about your bid and cost, a customer "will get it" and then start to wonder why the other guys didnt do this,, making you appear to have the best plan.

im assuming your talking about 30 or 42pos panel boards with OCP...... i most certainly would make sure each panel had its own OCP.
someone asked you this earlier,, didnt see the answer. Rule of thumb i use is "if your sub panel is not within eyesight of the MDP, then the sub panel must have a main breaker. some would debate this and how/when its applied but at the end of the day it is a failsafe and the right thing to do.

 

[augie47]

I know there are a lot of mitigating factors, but when one thinks about residential loads, look at POCO's 25kva pot feeding 4 houses each on a # 2 AL

 

[electrofelon]

I know there are a lot of mitigating factors, but when one thinks about residential loads, look at POCO's 25kva pot feeding 4 houses each on a # 2 AL

Yeah ive always thought about that. Try running 200 amps from your 200 amp service and see how long before the utility transformer destroys itself?

Rule of thumb i use is "if your sub panel is not within eyesight of the MDP, then the sub panel must have a main breaker. some would debate this and how/when its applied but at the end of the day it is a failsafe and the right thing to do.

Ill debate it. What would be the purpose of the main breaker in a "sub panel" (ignoring situations like taps and remote structures)?

 

[ActionDave]

Rule of thumb i use is "if your sub panel is not within eyesight of the MDP, then the sub panel must have a main breaker. some would debate this and how/when its applied but at the end of the day it is a failsafe and the right thing to do.

I don't see how a sub-panel without a main breaker is any less safe than one with.

 

[iwire]

I personally would design each room with 50% outlets and 50% lights on dedicated circuits.
meaning a basic bedroom would have 2 sources for lights and 2 sources for outlets.
When your asked about your bid and cost, a customer "will get it" and then start to wonder why the other guys didnt do this,, making you appear to have the best plan.

So each room would have four circuits?


This seems nuts to me, and wasteful with the AFCIs required.


How many rooms would one circuit jump too?

 

[augie47]

I personally would design each room with 50% outlets and 50% lights on dedicated circuits.
meaning a basic bedroom would have 2 sources for lights and 2 sources for outlets.
When your asked about your bid and cost, a customer "will get it" and then start to wonder why the other guys didnt do this,, making you appear to have the best plan.

.

No doubt there may be some customers who might react that way, but the majority I see are primarily interested in cost. Many don't even like to cost of a job that meets minimum Code.
If your philosophy worked, no one would be driving lower cost vehicles.

 

[jcassity]

well, it could be a cost adder i agree but on a personal note, my old log home here in WV has redundant circuits per room.
some customers dont understand the vast difference between best cost vs best price. so along with the blue light speacial, cheaper must be better right?

i see minds changing everyday with respect to this. I see customers wanting the best thing possible at the "best price".

on my projects i am looking for things in this exact order
-are you experienced working in this enviroment
-are you qulified to do the job
-are you able to react to my time frames with manpower
-are you priced right
every dollor you spend wrong today will cost you 2$ to fix, thats why the cost of a service comes 4th, the preceeding 3 build the foundation to prevent such an issue.



wow,, way off topic,, sorry to the OP~!

 

[Dennis Alwon]

a cost adder and a panel directory nightmare.

 

[jcassity]

the unfortunate truth is that 9 times out of 10 guys grab a sharpie or a pencil and start writting out panel schedules,, crossing stuff out and making it look bad. Its a problem they bring on themselves.

on my jobs, any changes to panel schedules warrant the document to be pulled out and typed up again,, its a cost the customer paid for and a sign of quality workmanship,, also a very very cheap and inexpensive high visibility item the customer can see.. and such an easy cherry picking technique to secure future projects.
not sure what the panel schedule nightmare is.. from my side of the fence, if you can clearly explain your engineering , theres isnt an issue.

this is how im wired,, doesnt look hard
1) Master Bed O/L #1 2) Master Bed O/L #2
3) Master bed Lgts 4) Lvg Rm 0/L #1
5) Lvg Rm O/L #2 5) Lvg Rm Lgts

 

[Greg1707]

400 amp service

400 amp service

In my area I have seen modest houses (3,000 square foot) have the service upgraded from 200 to 400 amp. When asking why I have been told, even by electricians, that a 400 amp service is better than a 200 amp service. I suppose it is better for the contractors bank account? Does anyone do load calculations any more for residential?

 

[Dennis Alwon]

the unfortunate truth is that 9 times out of 10 guys grab a sharpie or a pencil and start writting out panel schedules,, crossing stuff out and making it look bad. Its a problem they bring on themselves.

on my jobs, any changes to panel schedules warrant the document to be pulled out and typed up again,, its a cost the customer paid for and a sign of quality workmanship,, also a very very cheap and inexpensive high visibility item the customer can see.. and such an easy cherry picking technique to secure future projects.
not sure what the panel schedule nightmare is.. from my side of the fence, if you can clearly explain your engineering , theres isnt an issue.

this is how im wired,, doesnt look hard
1) Master Bed O/L #1 2) Master Bed O/L #2
3) Master bed Lgts 4) Lvg Rm 0/L #1
5) Lvg Rm O/L #2 5) Lvg Rm Lgts

IMO that schedule doesn't say as much as I would like. I would prefer 1) master bedroom receptacles 2) bedroom Lights, 3) Kitchen receptacles right side of sink, etc. I laser print the schedule so it is pretty inclusive

 

[JDB3]

I would find it hard to supply a bedroom with 2 circuits for the lighting & receptacle circuit. Most of the houses I wire have a ceiling fan with light kit, try putting that on 2 circuits. Sounds like an overkill to me.