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Old 02-05-2013, 09:18 PM   #1
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finishing basement and need to add subpanel


have a 1600 sqft basement unfished now but going to finish, looking at having a large living room, with kitchen (fridge, micro, dishwasher, maybe elec. stove.
1 or 2 bedroom, small bathroom with shower, hallway, and of course the existing utility area along with a storage room.

home is only 5 years old, have a 200 amp panel now, my main question is how do you know what size of sub panel you can put in, is there a limit, i know i dont want to trip my main 200, or the new ?? subpanel, but can you put in a 100amp sub panel or 75 or 50, are there guidlines to max size of subpanel you can put in, im guessing at this point the new panel might have 6 or 7 circuites, 20 amps for bathroom, kitchen and entertainment area of living room and 15 amps for the rest possibly, thinking one 15 amp circuit might be enough for all lights in basement since we use all cfl's, not sure if putting in can lights in the living room as it might take around 10 or so, didnt really calculate that but not sure that is the most cost effective route to go,

on the main panel, just so we know i do have a dual 30/20 amp breaker running 220 out to a sub panel outside for the hottub.

how does one know if they have enough power in their main panel to support their new addition (finishing of the basement) and what size sub panel they can legally/should go with?
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Old 02-05-2013, 09:41 PM   #2
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finishing basement and need to add subpanel


The stove will require a 40 or 50 amp breaker.
The kitchen will require 2 20 amp circuits.
The bathroom will require 1 20 amp circuit.
The microwave may require a dedicated circuit.


The main panel will have a listing of the largest branch breaker allowed, so you can't go any larger than the listing.

Do you have an electric stove, water heater, furnace now?
What are you going to use to heat and cool the basement?
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Old 02-05-2013, 09:49 PM   #3
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finishing basement and need to add subpanel


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The stove will require a 40 or 50 amp breaker.
The kitchen will require 2 20 amp circuits.
The bathroom will require 1 20 amp circuit.
The microwave may require a dedicated circuit.


The main panel will have a listing of the largest branch breaker allowed, so you can't go any larger than the listing.

Do you have an electric stove, water heater, furnace now?
What are you going to use to heat and cool the basement?
we have gas stove upstairs, basement is already heated, cooled by main house system, we have gas water heater, gas furnace..
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Old 02-05-2013, 09:49 PM   #4
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finishing basement and need to add subpanel


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Originally Posted by muellertr View Post
have a 1600 sqft basement unfished now but going to finish, looking at having a large living room, with kitchen (fridge, micro, dishwasher, maybe elec. stove.... have a 200 amp panel now,

my main question is how do you know what size of sub panel you can put in, is there a limit, i know i dont want to trip my main 200, or the new ?? subpanel, but...
The term is "load calculation"
You add up everything and see where you are.

Few 200A panels come close to capacity....
but adding a second set of loads to a home... will add up.

The reason most add a second panel is for "breaker space"...
you need room for those extra circuits.
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Old 02-05-2013, 10:00 PM   #5
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finishing basement and need to add subpanel


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Originally Posted by TarheelTerp View Post
The term is "load calculation"
You add up everything and see where you are.

Few 200A panels come close to capacity....
but adding a second set of loads to a home... will add up.

The reason most add a second panel is for "breaker space"...
you need room for those extra circuits.
What he said ....load calculations but you could install a 100 amp breaker as a basement main and do al you need worst case scenario 100 amp breaker trips but very unlikely

Last edited by RAUL HIDALGO; 02-05-2013 at 10:03 PM.
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Old 02-05-2013, 10:10 PM   #6
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finishing basement and need to add subpanel


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Originally Posted by RAUL HIDALGO View Post
What he said ....load calculations but you could install a 100 amp breaker as a basement main and do al you need worst case scenario 100 amp breaker trips but very unlikely
so yes, i need more breaker space, i only have 1 or 2 open and may need 7 or so, im pretty sure my 200 amps total is enough, but need room, so are there any rules that say i cant add 100 amp sub panel, or can you add any size you like? you said install a 100 amp breaker, im guessing you meant sub panel with 100 amp breaker, as i need the extra circuit room?>
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Old 02-05-2013, 10:14 PM   #7
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finishing basement and need to add subpanel


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Originally Posted by jbfan View Post
The stove will require a 40 or 50 amp breaker.
The kitchen will require 2 20 amp circuits.
The bathroom will require 1 20 amp circuit.
The microwave may require a dedicated circuit.


The main panel will have a listing of the largest branch breaker allowed, so you can't go any larger than the listing.

Do you have an electric stove, water heater, furnace now?
What are you going to use to heat and cool the basement?
YOu said the main panel will list the largest branch it can handle, since im needing a sub panel for extra circuit room, are you saying this will mean that number will be the max size of sub panel i can put in, or did you just mean the largest size breaker i could put in the existing panel, as that is not what i need, i need more circuit space... just need to make sure i can jump over off of the main feeds from the main box and put in a sub panel or likely 100amp is what im thinking would be a safe amount... dont need an electrical inspector showing up and saying a 100 amp sub panel is too big to run off of my 200 amp main panel... but i do think 100 amps is enough for the basement.
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Old 02-05-2013, 10:38 PM   #8
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finishing basement and need to add subpanel


You can add a 200 amp sub panel if you like, but the panel you have now will limit you to a 100 amp breaker.
The size of the sub you are concerned with is the number of circuits it has.

Buy a 125 amp panel with 24 circuits and protect it with the 100 amp breaker and you will have plenty of space.

Check on line and you will find site to do a load calculation.
As long as you do not exceed the size of the breaker feeding the sub, plus the size of the main you will be fine.

Do a search of this site and you will find many threads on installing a sub panel.

If you install can lights, the load is figured by the max wattage bulb you can place in them, not the size you want to use.
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Old 02-05-2013, 10:47 PM   #9
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Originally Posted by jbfan View Post
You can add a 200 amp sub panel if you like, but the panel you have now will limit you to a 100 amp breaker.
The size of the sub you are concerned with is the number of circuits it has.

Buy a 125 amp panel with 24 circuits and protect it with the 100 amp breaker and you will have plenty of space.

Check on line and you will find site to do a load calculation.
As long as you do not exceed the size of the breaker feeding the sub, plus the size of the main you will be fine.

Do a search of this site and you will find many threads on installing a sub panel.

If you install can lights, the load is figured by the max wattage bulb you can place in them, not the size you want to use.
so let me get this straight, i was thinking the sub panel would connect to the main panel by like some 4 gauge wire off of the same spot where the main feeds from outside connect to my main panel, but it sounds like you are saying that the sub panel has to connect off of actual "breaker slots" that are in my main, which would be why everyone is saying you have to make sure of what your max breaker size allowed on the main is, ... if that is the case, then this makes sense... but i was under the thought process that i could bypass the breaker section of my main and run big wire over to another "sub panel" or fuse box. and it would have one large breaker at the top like my main does, say 100 amp or so. basically meaning that none of the power would be running through my 200 amp breaker, just straight over to the built in 100 amp breaker in the new panel i put in, can i not do it that way? i actually have to go out of the breaker slots of my main?.. do they make a 100 amp breaker that fits into a single pole breaker slot? and if so, what size of wire do you run out of the 100 amp "new breaker in the main" that i just put in , to jump over to the sub panel?
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Old 02-06-2013, 12:00 AM   #10
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finishing basement and need to add subpanel


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Originally Posted by muellertr View Post
so let me get this straight, i was thinking the sub panel would connect to the main panel by like some 4 gauge wire off of the same spot where the main feeds from outside connect to my main panel, but it sounds like you are saying that the sub panel has to connect off of actual "breaker slots" that are in my main, which would be why everyone is saying you have to make sure of what your max breaker size allowed on the main is, ... if that is the case, then this makes sense... but i was under the thought process that i could bypass the breaker section of my main and run big wire over to another "sub panel" or fuse box. and it would have one large breaker at the top like my main does, say 100 amp or so. basically meaning that none of the power would be running through my 200 amp breaker, just straight over to the built in 100 amp breaker in the new panel i put in, can i not do it that way? i actually have to go out of the breaker slots of my main?.. do they make a 100 amp breaker that fits into a single pole breaker slot? and if so, what size of wire do you run out of the 100 amp "new breaker in the main" that i just put in , to jump over to the sub panel?
I will get this straghten out what Jbfan mention here .,

First of all ., The max size of the breaker you can install in the QO panel as you posted generally 100 amp.

Depending on how much room you have in the panel if you have two empty slots ( it will required double pole breaker ) it will work fine however there is other issue it may show up is the netural bussbar you may need to buy a adpator ( AN70 or AN100 ) due the oringal bussbar only can take #6 the most unless you get lucky that you have one space is larger that take big as #2 so that is a 50/50 chance on that part.

The 200 amp main breaker will protect everything including the "new " subpanel as well so don't mess with it.

I know you say 4 gauge that is too light for 100 amp but which materal it will be copper or alum. really from my part I rather run with #3 copper that is good for 100 amp but if you really need #4 copper IIRC it will required 80 amp breaker ( I know some are listed for 80 or 85 amp but you will not find 85 amp breaker )

#2 alum is good for 90 or 100 amp depending on which type of conductor itself

I know Jbfan mention 125 amp main lug 24 space panel that is common item and I am sure you will find this in big box store ( sometime it cheaper get one with factory 100 amp main breaker inclulded so take it )

Keep the netural and ground conductor seperated on subpanel and pretty good percentage you will end up buy a ground bussbar which they useally run about 7 to 10 Euros.(dollars) and do not use the bonding screw or jumper strap discharge them ya don't need it in subpanel useage.

Merci,
Marc
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Old 02-06-2013, 12:09 AM   #11
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I will get this straghten out what Jbfan mention here .,

First of all ., The max size of the breaker you can install in the QO panel as you posted generally 100 amp.

Depending on how much room you have in the panel if you have two empty slots ( it will required double pole breaker ) it will work fine however there is other issue it may show up is the netural bussbar you may need to buy a adpator ( AN70 or AN100 ) due the oringal bussbar only can take #6 the most unless you get lucky that you have one space is larger that take big as #2 so that is a 50/50 chance on that part.

The 200 amp main breaker will protect everything including the "new " subpanel as well so don't mess with it.

I know you say 4 gauge that is too light for 100 amp but which materal it will be copper or alum. really from my part I rather run with #3 copper that is good for 100 amp but if you really need #4 copper IIRC it will required 80 amp breaker ( I know some are listed for 80 or 85 amp but you will not find 85 amp breaker )

#2 alum is good for 90 or 100 amp depending on which type of conductor itself

I know Jbfan mention 125 amp main lug 24 space panel that is common item and I am sure you will find this in big box store ( sometime it cheaper get one with factory 100 amp main breaker inclulded so take it )

Keep the netural and ground conductor seperated on subpanel and pretty good percentage you will end up buy a ground bussbar which they useally run about 7 to 10 Euros.(dollars) and do not use the bonding screw or jumper strap discharge them ya don't need it in subpanel useage.

Merci,
Marc
so. i install a 2 slot 100 amp breaker, and out of that are going to be two wires which travel over to feed the sub panel, we are saying #3 copper for both of these wires? and the output side of this double slot 100 amp breaker is going to be big enough to let me put #3 wire in it? and then since these are being regulated by the 100 amp double slot breaker i just put in, the sub panel i install wont need a "main breaker" like the 200 amp breaker in my existing box, just 15 and 20 amp breakers for each circuit, is this correct, because my initial thinking was that i would run power over from where the main feeds from outside of the house connect to the main breaker box straight over to the feeds/inputs of the new sub panel, i was expecting to have to have a subpanel that had its own "main breaker" at the top, like a 100 amp(one that presumably came already in the subpanel when i bought it).
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Old 02-06-2013, 06:03 AM   #12
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finishing basement and need to add subpanel


This seems like a very large project. You are basically building a home within a home. Do you know all the codes associated with this? 2nd path of egress? AFCI's? Outlet spacing (general and countertop)? Possible cutting of concrete for drains? Have you consulted are are you using a contractor? Where are you located?
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Old 02-06-2013, 06:14 AM   #13
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so. i install a 2 slot 100 amp breaker, and out of that are going to be two wires which travel over to feed the sub panel, we are saying #3 copper for both of these wires? and the output side of this double slot 100 amp breaker is going to be big enough to let me put #3 wire in it? and then since these are being regulated by the 100 amp double slot breaker i just put in, the sub panel i install wont need a "main breaker" like the 200 amp breaker in my existing box, just 15 and 20 amp breakers for each circuit, is this correct, because my initial thinking was that i would run power over from where the main feeds from outside of the house connect to the main breaker box straight over to the feeds/inputs of the new sub panel, i was expecting to have to have a subpanel that had its own "main breaker" at the top, like a 100 amp(one that presumably came already in the subpanel when i bought it).
The lugs in the 200 amp panel are not rated for two conductors.
Follow the advice from the otther posts.
1. Install 100 amp breaker in main panel
2 Run 100 amp ser from 100 amp breaker in main panel to subpanel. Subpanel could be 100 amp main breaker panel.
3. Make sure that neutrals and grounds are seperated in subpanel. Going to have to install ground bar in subpanel.
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Old 02-06-2013, 07:28 AM   #14
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The lugs in the 200 amp panel are not rated for two conductors.
Follow the advice from the otther posts.
1. Install 100 amp breaker in main panel
2 Run 100 amp ser from 100 amp breaker in main panel to subpanel. Subpanel could be 100 amp main breaker panel.
3. Make sure that neutrals and grounds are seperated in subpanel. Going to have to install ground bar in subpanel.
ok...im getting close, but for someone not so inclined, everyones answer helps me some, but i am putting it all together, i will number these, and if any step is wrong, let me know

1. install 100 amp 2 pole breaker in main box (this will feed the two hot wires to my sub box

2. i will most likely try to find 100 amp main panel for the sub, sounds like they might be cheaper from what people have said just due to them being mass produced.

3. i will have to run 4 wires between main and my new sub

4. run 2 #4 copper from the 100 amp breaker to the lugs in the new sub( i was not aware that that individual breakers would accept wires this big, so this provided some confusion to me, but im guessing since its 100 amp maybe the holes in the breaker where you attach the wire are larger than normal 15 and 20 amp breakers?

5. run 1 #4 copper from nuetral in main to nuetral in sub

6. run 1 #8 copper from ground in main to ground in sub

7. make sure to disconnect nuetrand and ground buss in the sub, as they can only be connected in your main.. (not sure yet how to find this but once i have it in front of my face it should be pretty easy to see.

8. it was said i might have to install a ground bar in sub panel, shouldn't the new panel have a neutral and a ground buss already in it? seems like all panels i have ever seen always have to long busses for attaching all of your circuit nuetrals and grounds (one for each)? or are we talking about something else. is this ground bar we are talking about not one of the buss bars that has all of the small individual screw terminals for one wire from each circuit like im envisioning in my head?

9. I think ill add a picture later today or tonight and lable it of the inside of a sub to make sure what i have envisioned is correct, that shouldnt leave any gray area in my mind.

10. and last but not least, i have seen people post in other sites that it might be cheaper for wire, and maybe the breaker box to find them through electrical wholesalers, i live in basically des moine iowa, so large enough area. will there be places that will sell to the general public, if so any tips on what to search for online, what are they called? electrical wholesaler, electrical supplier, electrical distributor? any tips? I still have to wire all the circuits in the whole basement so will need quite abit of 12-3 wire, what is a typical price for either 250 or 500 foot rolls of this, im sure it varies for different parts of the country someone should know what you find it for compared to big box store prices.

photo will be coming later today or tonight to show my final interpretation of all of this.. thank you all for your help, this is such a great site...
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Old 02-06-2013, 07:32 AM   #15
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finishing basement and need to add subpanel


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Originally Posted by muellertr View Post
ok...im getting close, but for someone not so inclined, everyones answer helps me some, but i am putting it all together, i will number these, and if any step is wrong, let me know

1. install 100 amp 2 pole breaker in main box (this will feed the two hot wires to my sub box

2. i will most likely try to find 100 amp main panel for the sub, sounds like they might be cheaper from what people have said just due to them being mass produced.

3. i will have to run 4 wires between main and my new sub

4. run 2 #4 copper from the 100 amp breaker to the lugs in the new sub( i was not aware that that individual breakers would accept wires this big, so this provided some confusion to me, but im guessing since its 100 amp maybe the holes in the breaker where you attach the wire are larger than normal 15 and 20 amp breakers?

5. run 1 #4 copper from nuetral in main to nuetral in sub

6. run 1 #8 copper from ground in main to ground in sub

7. make sure to disconnect nuetrand and ground buss in the sub, as they can only be connected in your main.. (not sure yet how to find this but once i have it in front of my face it should be pretty easy to see.

8. it was said i might have to install a ground bar in sub panel, shouldn't the new panel have a neutral and a ground buss already in it? seems like all panels i have ever seen always have to long busses for attaching all of your circuit nuetrals and grounds (one for each)? or are we talking about something else. is this ground bar we are talking about not one of the buss bars that has all of the small individual screw terminals for one wire from each circuit like im envisioning in my head?

9. I think ill add a picture later today or tonight and lable it of the inside of a sub to make sure what i have envisioned is correct, that shouldnt leave any gray area in my mind.

10. and last but not least, i have seen people post in other sites that it might be cheaper for wire, and maybe the breaker box to find them through electrical wholesalers, i live in basically des moine iowa, so large enough area. will there be places that will sell to the general public, if so any tips on what to search for online, what are they called? electrical wholesaler, electrical supplier, electrical distributor? any tips? I still have to wire all the circuits in the whole basement so will need quite abit of 12-3 wire, what is a typical price for either 250 or 500 foot rolls of this, im sure it varies for different parts of the country someone should know what you find it for compared to big box store prices.

photo will be coming later today or tonight to show my final interpretation of all of this.. thank you all for your help, this is such a great site...
Where did you get that #4 copper is good for 100A?

Mark
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