how many subpanels?

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cceinak

Member
I have a quick question about subpanels:

Is there a limit to the number of subpanels you can have in a house? We are working on a very large home with three very distinct floors.
The owner would like to have a main distribution panel in his mechanical room on the bottom floor that did nothing but feed 4 other subpanels. I guess in a sense, its just like an I line panel you find in a more commercial application. Has anybody ever installed an electrical application like this? The owner would like this main distribution panel in the mechanical room and would also included a 60 amp subpanel that would feed all the mechanical applications for his house. This 60-amp sub would be tied into a generator transfer switch so he could keep all the vital systems of his house on line incase of electrical failure. I think he wants to put a few vital branch ckts from through out the house on here as well. The other three panels would feed each separate floor. Can anybody see any problems with this? There is the obvious things, like making sure the panel is rated for the amps feeding it, making sure the breakers all have the same short circuit rating, but if you have a main disconnect on the outside of house, and a main 200 amp breaker in the panel, is there a problem with a panel having three 100 amp main breakers and a 60? Thanks in advance, and if anybody has any better ideas, I would love to pass them on! Also, the feeder calculations for the entire house are under 200 amps.
 
tonyi

tonyi

Senior Member
Re: how many subpanels?

The guy is sharp - this is a very good way to design a multi-story building for future expansions and it will cut your installation labor considerably as well.

You could have a dozen 100A feeders coming out of a 200A main - not a problem. These 100A panels could in turn feed a dozen more 100A panels each, etc, etc.

The key things to consider are what loads are likely to be on at the same times on each floor.

You may want to color code the hot legs of each feeder so you can keep the whole buildings hot leg loads distributed evenly easier. Haphazardly plunking stuff into the 100A panels without considering leg could load one of the 200A legs up more than the other and cause a main trip before it really needed to occur if things were located a little different.

Might also consider taking a 200A feeder all the way to the 3rd floor and tapping it at each floor for main breaker panels. If future needs ever called for a lot of power on one floor, it'll always be there. With 200A capable taps and panels full power could be had anywhere. The "mains" on these subs could be smaller backfed 50/60/70/100A 2-poles for the present with the 200A main breaker ignored. Better to trip a small local breaker than have it be a race between the building main and a sub's. If any given floor tripped out on overload, it wouldn't require a trip to the basement to resolve.

To save some cost, a main convertable 200A MLO panel could be used. Ignore the lugs and backfeed the appropriate sized breaker for the floor's current needs.

[ November 19, 2003, 12:44 AM: Message edited by: tonyi ]
 
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ty

Senior Member
Location
3rd Rock from the Sun
Re: how many subpanels?

What you are suggesting is done quite frequently.
I would make the 60amp a 100amp. for numerous reasons (but they might not apply to you):
Cost- we get the 100amp for the same as the 60.
Expansion- the automatic transfer switches that we install come in 50, or 100amp.
Stock- we have the 100amp materials in our stock.
Less confusion for the installer also.
My concerns are:
I know that you state 'the feeder calculation for the entire house are under 200amps', but is it really? Are you positive that nothing got overlooked in the calculation? What is the square footage of this house?
From your own description, this is 'a very large home with three very distinct floors'. In my experience, the size home that I'm imagining could easily go over 200amps and then some.
If you're certain about the 200amp, then go for it. The 'subpanels' will make for less voltage drop on homeruns and quicker wire pulling time.
 
A

a.wayne3@verizon.net

Guest
Re: how many subpanels?

Three distict floors with a 200 AMP MAIN???How many A/c units are there ??? is this a gas area??
To many variables on that one ......We did 32,000 sq ft home a few years ago and set an 800 amp ct service with 5 sub panels (200 each) and a 150 amp landscape panel.This was essential to ensure that there were short homeruns.the load calc was at 475 but i opted to go to 800 to ensure that later on the lights would stay bright when A/c`s kicked in.Any thoughts ????????
 
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cceinak

Member
Re: how many subpanels?

hello,
a little more info on the house, its about 6000 sq minus non living. The calcs I did actually came out to around 140 amps total. This is in interior alaska, no AC needed. Hot water heater is tied into coil on fuel oil boilder. Main loads are range, 8000 VA, Dryer, 5500 VA then your common in place appliances. Its amazing about how few lighting branch Ckts you actually need for a house if you use the code. Anyhow, 6000 sq is pretty big for just two people and they are thinking about maybe a bed and breakfast or something else later. OH, also, the wife has MS so he really wants a panel on every floor just in case a breaker trips, his wife does not have to climb stairs or something to reset. Kind of overkill, but hey, if you got the money, why not? Actually I am really excited, its nice to do a project where the customer does not want to cut any corners.
 
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wildman

Senior Member
Location
Georgia
Re: how many subpanels?

tonyi...ty...ryan...pierre......just finished reading your posts on "sub-panels"...was reading on another forum and almost convinced the word sub-panel is a no..no! they should be called "main panel extentions"....anyway, my "main panel" is 200 amps. my first panel extention is 100 amps fed from a 100 amp breaker in my "main" panel. my second panel extention is a 125 amp (spa) panel fed from a 100 amp breaker in my first panel extention. the first panel extention is located inside the house...the second panel extention is located on the exterior wall of the house..It contains a 2-pole gfci breaker for the hot-tub and two single pole gfci breakers for outside lighting and receptacles.(2-pole 50 and two single pole 20's...I understand this is acceptable?
 
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wildman

Senior Member
Location
Georgia
Re: how many subpanels?

just read my post and don't want to be confusing....the question is...feeding a spa panel from a subpanel is ok or should I feed the two subpanels from the main panel? thanks!
 
tonyi

tonyi

Senior Member
Re: how many subpanels?

Feeding the spa panel from a sub is OK.

If you had an outside 3R disconnect for the house service (w/out slots) its going to be essentially impossible to do it otherwise - the disco is the "main" and whatever is inside is a sub.
 
hornetd

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
Re: how many subpanels?

I have used this same technique when doing a heavy up for persons of limited means when the existing service had modern panels supplied from auxilliary terminals in older service equipment. By converting the modern panels to feeder supplied lighting and appliance or power panelboards I saved the customer the cost of rewiring all of the branch circuits.
--
Tom
 
tonyi

tonyi

Senior Member
Re: how many subpanels?

Last saturday a tree falling on the lines cleaned the whole service right off my parent's old homstead. I up to 200A, 3R 200A disco to a 12 slot 200A MLO (feeder distribution and basement services) in a much more strategically located area in preparation for a major rewire in the future and temporarily backfed the old junk to keep everything live in the interim.

I wasn't thinking in terms of cost, rather future flexibility, but you're right, in the old service gear/modern panel scenario, this is a perfectly viable thing to do - and the fire company will be a lot happier with the outide disco. Not many setups like this in northern NY - the inspector was impressed :)
 
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tshephard

Member
Re: how many subpanels?

Based on your occupancy, I would try to get customer to consider allowing for a future elevator or 2 of those stair-gliding machines. Be a lot easier now.
 
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wildman

Senior Member
Location
Georgia
Re: how many subpanels?

tonyi...thanks for your post! there is no "out side disc." service leaves meterbase and travels approximately 35 feet through the attic to the 200 amp (20) space panel! added 2-pole 100 amp breaker to feed 100 amp panel downstairs for water heater...downstairs lighting and receptacles....want to add a 100 amp breaker to feed outside spa panel for hot tub(50 amp) and 2-20 amp breakers for outside lighting, receptacles, etc. thanks again!
 
tonyi

tonyi

Senior Member
Re: how many subpanels?

Ouch - the inspectors I know would balk for sure at 35' of SE running through an attic to a main.
 
W

wildman

Senior Member
Location
Georgia
Re: how many subpanels?

tonyi....house is 22 years old....200 amp panel is located near the center of the house in the hall way...this is a subdivision...been in several of the houses....panels are located approximately same distance from meter base...no outside disc....inspector may not approve of it now...but it must of been ok when houses were built! If I were to upgrade, inspector will require and outside disc. are you considering a "subpanel" as an upgrade? wildman
 
tonyi

tonyi

Senior Member
Re: how many subpanels?

I think I'd give the inspector a call first. Describe the situation and ask for some guidance before tearing into this one.
 
G

gwz2

Senior Member
Location
Indiana
Re: how many subpanels?

Must be an AREA of the country where there is not inspections, or an area where 'Drive By ' inspection is the norm, for such a long run of SE cable in an attic.

Of course, maybe the inspector is lent to the building department from refuge department because he is the mayor's son-in-law's brother.

gwz2
 
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