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Old 07-29-2012, 10:35 AM   #1
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Help New Addition Electrical Sub Panel/Load


I am in the process of building an addition. I am at the point of wiring the addition. I plan on using the space for a kitchen and small living room. I would like to run all the wiring and install a sub panel in the additions basement on my own. As far as providing power to the sub panel or updating the main service panel I will probably leave this for an electrician, who already stated he would evaluate my work. I want to make sure I install the correct size sub panel with the proper amps. I have questions about the electrical loads, if an updated service panel is required and suggestions with the installation of the sub panel. I want to make sure I am installing the electric components correctly.

Overall I plan on using a sub panel feeder breaker to power the sub panel, which will be placed 24’ from the service panel. I would like to power all the addition through the sub panel and not have to run any circuits back to the main service panel. I figure if I do upgrade to 200 amps, I will place a 100 amp feeder breaker in the main service panel to feed the sub panel. Any recommendations or concern would be appreciated. Thank you.
Currently my house has a 100-amp service but I do not utilize all the amps. I have four open circuits and I will be taking out the 40-amp circuit for the range and placing it in the sub panel.

Here is info about my set up.

Currently the 100 amps services 1100 square foot home with a range, dryer, washer, refrigerator, gas furnace, and two-window ac’s.

Electrical Load Calculation including new appliances.

So the final electrical load would be:
1. 1591 square feet home.
2. 2 kitchen small appliance circuits
3. 1 laundry circuit.
Permanent appliances will be: watts were found on appliances.
  • Double wall oven 4000 watts. Placed in sub panel.
  • Cook top 6550 watts. Placed in sub panel.
  • Dishwasher 1500 watts. Placed in sub panel.
  • Dryer 5000 watts.
  • Washer 1000 watts.
  • refrige 500 watts.
  • Gas furnace 800 watts.
  • Microwave 1000 watts.
  • Window ac’s 2220 watts.
  • Portable heat 1000 watts.
  • Baseboard heat 3000 watts. Placed in sub panel.
Out door usage is 720 watts.

After doing calculations I come up with 89 amps. Does this sound right? Since the service panel is rated for 125 amps less 20% shouldn’t the service be adequate? Do I need to update the service panel to 200 amps?

Here are the new circuits I will be adding. Total of 10 circuits.
  • 20 amp small appliance 7 receptacles.
  • 15-amp Kitchen area lighting including 7 recessed lights and two switches.
  • 15 amp Living room lighting total of 4 ceiling box’s and two switches.
  • 40-amp range circuit.
  • 40-amp cook top circuit.
  • 15-amp dishwasher circuit.
  • Living room 15 amp receptacles on arc fault total of 6.
  • 20-amp microwave circuit.
  • 240-volt electric baseboard 2 6’ 1000 watt heaters.
  • 15 amp outdoor light and receptacle.


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Old 07-29-2012, 11:16 AM   #2
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Help New Addition Electrical Sub Panel/Load


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Originally Posted by RISurfer View Post
I am in the process of building an addition.
I want to make sure I am installing the electric components correctly.
Start with a few books and videos to see the more common approaches to HOW it all gets done... then follow these.

The most common source of DIY problems is when they get "an idea" or believe their situation calls for X vs the far more common Y; and so forth.
Avoid this.

If you ever have a specific question... ask it.

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Old 07-29-2012, 11:17 AM   #3
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Help New Addition Electrical Sub Panel/Load


Disposal? Well pump? Water heater?
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Old 07-29-2012, 12:34 PM   #4
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What does your electrician say? I am on the fence. You are probably pushing a 100A service, but it doesn't appear that you NEED to upgrade to 200A. Do you ever plan on installing central air? That may help you make the decision.
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Old 07-29-2012, 01:14 PM   #5
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Help New Addition Electrical Sub Panel/Load


The thing with a main breaker and the amperage rating of a subpanel is what *all* will you ever possibly have powered on AT THE SAME TIME.

You can have 400 amps of outlets, but only use 60 amps total at any one time, so a 100 amp main breaker would do fine (in that case).

Or say somewhere like a wood shop where they have many workers and all the machines are all on at the same time, then the main breaker would need to exceed the total amperage of everything.

And not everything in a kitchen would be powered on at the same time. I think the best test is Thanksgiving and a lot of people over. Lots of things on in every room of the house and lots of things on all at once in the kitchen. Maybe several people in the kitchen using various appliances at the same time - Grandpa's RV plugged into the house. Etc.

So far as a subpanel, that can be determined by the largest breaker you can get for that to install in your main panel. Also the wire size can be very large and difficult to snake into the panel and to the subpanel, especially if aluminum. Copper of a large size can cost a small fortune, but will be smaller for the same amperage rating.

Might want to go look at breakers for your main panel and the wire sizes for say 100 amps or 125 amps. Note this needs to be 4 wires for a subpanel - Hot, hot, neutral, ground.

If your main panel is currently "crammed" with wires and there is no way you could fit additional large wires and a double breaker in there, that might be a consideration to upgrade and get a more "roomy" main panel.
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Old 07-29-2012, 01:33 PM   #6
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Quote:
Note this needs to be 4 wires for a subpanel - Hot, hot, neutral, ground.
Not if you use EMT.
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Old 07-29-2012, 04:24 PM   #7
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Disposal? Well pump? Water heater?
Just a water heater which runs on gas.
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Old 07-29-2012, 04:34 PM   #8
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Help New Addition Electrical Sub Panel/Load


I have four circuits open in the main service panel. I am just trying to figure out the best scenario for the additions electrical. Is the best scenario to upgrade the main to 200 amps and run all the new wire back 24' to the main service? Or should I install a sub panel in the addition and run the new wires to that? If I did run 10 circuits Back to the main panel can I run all the wires in one pipe of conduit? I am looking for suggestions. Thanks for the responses.
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Old 07-29-2012, 04:35 PM   #9
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Lets keep this as simple as possible, As stated, your 100 amp service is most likely adequate unless you want to add central air or a hot tub or other large appliance in the future...


If I was doing that job, I would run #2 SER AL. wire from the main panel to the sub-panel, fed with a 90amp breaker, I generally use 24 circuit / 125 amp panels. This should be more than generous for future circuits along with your addition.
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Old 07-29-2012, 04:36 PM   #10
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Help New Addition Electrical Sub Panel/Load


Quote:
Originally Posted by k_buz

Not if you use EMT.
Huh? I don't need 6-3 for my subpanel??
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Old 07-29-2012, 04:38 PM   #11
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Help New Addition Electrical Sub Panel/Load


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Originally Posted by ryan50hrl View Post
Huh? I don't need 6-3 for my subpanel??
EMT can be used as the grounding conductor.
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Old 07-29-2012, 05:10 PM   #12
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Help New Addition Electrical Sub Panel/Load


Quote:
Originally Posted by stickboy1375 View Post
Lets keep this as simple as possible, As stated, your 100 amp service is most likely adequate unless you want to add central air or a hot tub or other large appliance in the future...


If I was doing that job, I would run #2 SER AL. wire from the main panel to the sub-panel, fed with a 90amp breaker, I generally use 24 circuit / 125 amp panels. This should be more than generous for future circuits along with your addition.
Thanks. The 90 amp breaker won't effect the other circuits in the main? The sub Panel would be rated for 100 amps? Thanks for your help.
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Old 07-29-2012, 05:16 PM   #13
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Help New Addition Electrical Sub Panel/Load


Quote:
Originally Posted by RISurfer View Post
Thanks. The 90 amp breaker won't effect the other circuits in the main? The sub Panel would be rated for 100 amps? Thanks for your help.

The sub panel will most likely be rated for 125 amps, but you're supplying it will a 90 amp breaker. And besides, if you do upgrade to a 200 amp service down the road, this will be all set and one thing you wont have to mess with, I would leave some wire slack at the existing panel so you have no issues with a bigger panel later on.

Last edited by stickboy1375; 07-29-2012 at 05:20 PM.
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Old 07-29-2012, 08:42 PM   #14
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Thanks for the help stickboy.
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Old 07-29-2012, 09:33 PM   #15
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Quote:
Originally Posted by ryan50hrl View Post
Huh? I don't need 6-3 for my subpanel??
You could never use 6-3 for a 100A subpanel.

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