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Old 07-02-2009, 09:00 AM   #1
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New Addition - Thinking through electrical


I am in the planning stages of an addition and am considering electrical needs. I am sure our architect will get to it at some point, but I want to make sure there's sufficient room in the panel.

The addition is small, just 10'x5' on three different floors. On two of the floors the addition will function as a mudroom and on the other more of a reading nook/closet. On each floor, one of the 10' walls is filled with floor to ceiling cabinets. How many outlets am I going to need on each floor? Can I get by with just 1 per floor? I think so, but am not sure.

Additionally, we will add 3 flushmount lights (one on each floor), three exterior lights and 2 exterior outlets (one will power a 300 watt transformer).

So,I guess the question is, how many circuits would you suggest? Can I get by with 1 20 amp circuit, or is it just way too much?

On a related question, after the addition we will be adding a bathroom and renovating another (they will share one common wall). They are relatively small bathrooms, less than 50 sq. ft. each. We will be adding electric radiant in floor heat to both bathrooms. As the radiant heat is not placed under the tub/shower, vanity or toilet, the combined area for radiant heat between both bathrooms is less than 50 sq. ft. The instructions for the product call for a dedicated 20 amp circuit. The instructions also indicate that 150 sq. ft = 15 amps. So, would it be problematic to have the radiant heat for both bathrooms on 1 circuit? Both bathrooms together would use less than 5 amps.

Thanks for any insight!

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Old 07-02-2009, 11:07 AM   #2
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New Addition - Thinking through electrical


3 volt-amps per sq. ft of floor is one rule of thumb.

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Old 07-02-2009, 11:09 AM   #3
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If you have an architect, don't sweat this. You must have an electrical contractor too, right? Let them figure it out and you just tell them what you want done. Thats how it works.
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Old 07-02-2009, 11:35 AM   #4
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New Addition - Thinking through electrical


Thanks for the input. Yes, we have an architect, but she says it will be a while before we get to the electrical. I'm really just trying to see, more or less, what's coming down the road. As such, I'd appreciate any additional input.

I am doing the addition myself and and at this point anticipate doing the electrical as well.

In that this is a DIY forum, I was hopeful I could get some help. Any thoughts would be very much appreciated.

Last edited by stubits; 07-02-2009 at 11:38 AM.
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Old 07-02-2009, 12:22 PM   #5
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Originally Posted by stubits View Post
I am in the planning stages of an addition and am considering electrical needs. I am sure our architect will get to it at some point, but I want to make sure there's sufficient room in the panel.

The addition is small, just 10'x5' on three different floors.
3x50 = 150 sq. ft. x 3 va/sq. ft. = 450 va = ~4A @ 120v.
How many outlets am I going to need on each floor?

Probably at least 4 per room.

Can I get by with just 1 per floor?
You'll regret it. More bucks up front = less aggravation downstream.


Additionally, we will add 3 flushmount lights (one on each floor), three exterior lights and 2 exterior outlets (one will power a 300 watt transformer).
6x60w + 15A = 360w@120v = 3A + 15A = 18A.


So,I guess the question is, how many circuits would you suggest? Can I get by with 1 20 amp circuit, or is it just way too much?

On a related question, after the addition we will be adding a bathroom and renovating another (they will share one common wall). They are relatively small bathrooms, less than 50 sq. ft. each. We will be adding electric radiant in floor heat to both bathrooms. As the radiant heat is not placed under the tub/shower, vanity or toilet, the combined area for radiant heat between both bathrooms is less than 50 sq. ft. The instructions for the product call for a dedicated 20 amp circuit. The instructions also indicate that 150 sq. ft = 15 amps. So, would it be problematic to have the radiant heat for both bathrooms on 1 circuit? Both bathrooms together would use less than 5 amps.

Thanks for any insight!
What you need at a minimum to work, and what is code, can be two very different things, for reasons of safety, convenience, and many other reasons.

To cushion the sticker shock for your addition, get a half dozen books out of your local library on Residential Wiring. After spending 8 tedious hours wading through these books you will know way more about this.
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Old 07-02-2009, 12:45 PM   #6
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New Addition - Thinking through electrical


Think about what you ever might possibly use electrical in those rooms. In my experience there is NEVER enough outlets in certain spots!

Might you want a window air conditioner? Electric heater?

Might you want to place a fan in a window?

Maybe convert a room into an office? Phones, computer, 4-plex outlets for all that computer stuff?

Etc.

Then outlet for vacuuming. Will the new outlets be filled with plugs and there will not be a spare outlet for a vacuum.

Maybe outlet by door just for vacuum?

Basically walk through your house and think about where you wish you had more outlets and why.

Or see what all is blocking outlets and that maybe an outlet for a vacuum would be a good idea near a door.

Or look at areas where all the plugs are used up. No spare plugs and you wish there 4 outlets there instead of 2.

And would you want phones, cable TV, computer, etc.?

Ceiling lights?

Lights in closet which automatically come on when you open the door?
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Old 07-02-2009, 01:08 PM   #7
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New Addition - Thinking through electrical


As far as how many outlets (for a non-kitchen or non-bathroom), code basically states that there needs to be an outlet at least every 12 feet, horizontally, along uninterrupted wall surface. The theory is that if you put something along your wall and want to plug it in (such as a lamp), it shouldn't ever be more than 6' away from the nearest outlet in either direction. Doorways and closet doors; an outlet needs to be no more than 6' away from door openings.

And it sounds like the addition will add a new room to each floor (instead of just bumping out square footage of existing rooms). So each new room needs to have a switch by the door that controls either an overhead junction box/light, or a receptacle that will have a lighting fixture plugged into it.

As far as how many circuits, and what amperage, that all depends on what you plan on using in those rooms. If you're doing a window A/C in each room, you should most likely do a dedicated 20A circuit for each room. Basically, figure out the wattage of everything that will be in each room, and go from there, knowing that a 15A circuit provides about 1,800 watts and a 20A circuit provides 2,400 watts.
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Old 07-02-2009, 01:20 PM   #8
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New Addition - Thinking through electrical


Billy Bob and Adpanko, thanks so much for the advice. On two of the levels, the addition will be a mudroom with a full wall of storage. On the third level, the addition will serve as an annex for the bedroom and will house a full wall of storage as well as a window seat. We have central AC and heat, so no need for space heater or window AC. The earlier suggestion of 4 outlets per room seemed absurd. Aside from a vaccum, there is really no need for outlets in these spaces at all.
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Old 07-02-2009, 01:52 PM   #9
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The earlier suggestion of 4 outlets per room seemed absurd.
Wait and see!
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Old 07-02-2009, 02:23 PM   #10
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Quote:
Originally Posted by stubits View Post

On a related question, after the addition we will be adding a bathroom and renovating another (they will share one common wall). They are relatively small bathrooms, less than 50 sq. ft. each. We will be adding electric radiant in floor heat to both bathrooms. As the radiant heat is not placed under the tub/shower, vanity or toilet, the combined area for radiant heat between both bathrooms is less than 50 sq. ft. The instructions for the product call for a dedicated 20 amp circuit. The instructions also indicate that 150 sq. ft = 15 amps. So, would it be problematic to have the radiant heat for both bathrooms on 1 circuit? Both bathrooms together would use less than 5 amps.

Thanks for any insight!
Regarding future new bath and remodel of existing:

You will need a dedicated 20a ckt. for the new bath. It can service the GFCI, lights and fan but may not leave the bath to feed any other outlets. Or, you can use a dedicated 20a ckt to feed receptacles in both baths, but that circuit may not feed any other outlets (lights, fan, etc.). So at least 2 ckts for both baths (lights/fans/receptacles).

As an electrician, we wire devices (such as floor heat) to the manufacturer's specifications. So if it call for a dedicated circuit for each bath, that's what we'll do. The floor heat will need to be GFCI protected. Sometimes the thermostats have integral GFCI protections for the mats.

So, you are looking at 4 circuits for both baths. You should already have one present for the exisiting bath.

Do all your research for future circuitry while your walls are open. Especially if you need to circuits from the panel to the second floor.
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Old 07-02-2009, 05:21 PM   #11
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New Addition - Thinking through electrical


Yoyizit- As I explained in a previous post, the additions are less rooms and more closets/pantries. How many outlets do you have in your closets? I understand the desire to have the max number of outlets, but frankly between doors and cabinets, I don't have room for 4 outlets in each of these spaces.

Jupe Blue- Thanks for your insight here. I am aware that each bath needs a dedicated 20 amp circuit. I also understand why pros like yourself install things per the manufacturer's instructions... liability. Can you give me any insight into why each mat would require its own circuit, aside from the manufacturer's instructions? I am just looking to understand the how and why.

Thanks!
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Old 07-02-2009, 05:31 PM   #12
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Quote:
Originally Posted by stubits View Post
Yoyizit- As I explained in a previous post, the additions are less rooms and more closets/pantries. How many outlets do you have in your closets? I understand the desire to have the max number of outlets, but frankly between doors and cabinets, I don't have room for 4 outlets in each of these spaces.

Jupe Blue- Thanks for your insight here. I am aware that each bath needs a dedicated 20 amp circuit. I also understand why pros like yourself install things per the manufacturer's instructions... liability. Can you give me any insight into why each mat would require its own circuit, aside from the manufacturer's instructions? I am just looking to understand the how and why.

Thanks!
Sorry to disturb you.
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Old 07-02-2009, 07:57 PM   #13
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The earlier suggestion of 4 outlets per room seemed absurd. Aside from a vaccum, there is really no need for outlets in these spaces at all.
You don't get to decide.

Receps every 12'. Within 6' from the door. Every wall over 2' wide.
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Old 07-02-2009, 08:50 PM   #14
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Agreed, 1 outlet per wall plus every 12' is REQUIRED by code, plus what 220/221 said
You want to fail the inspection?
Why come on here & ask for help & then say you won't take the advice?
It's not advice, it's what's required
Just like the bathrooms need GFCI, bedrooms need AFCI
In some cases its not what you may use the house for, but a future owner
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Old 07-02-2009, 09:36 PM   #15
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In some cases its not what you may use the house for, but a future owner
Exactly. You do own your home but it has to be built to modern standards and specifications to insure it's value in the community.

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