Upgrading Sub Panel for Attached Garage

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Old 06-25-13, 01:29 PM
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Upgrading Sub Panel for Attached Garage

My garage sub panel doesn't have room to expand, and I am looking at installing some dedicated 240 equipment in my garage (air compressor & electric oven).

I purchased a Siemens 100 amp, 20 space, 20 circuit panel to use replace the existing sub panel in my garage. The physical work to replace the panel is not what I'm concerned about. I wanted some help in determining the load so I can make sure that I have the right sized breaker on my main panel & the correct wire to run to the panel.

The existing sub panel is on a 40 amp breaker in my main panel. It has 5 circuits currently. One lighting circuit, a separate circuit for outdoor lights, one circuit marked as a freezer circuit, and I believe the remaining two are general receptacle circuits. (going off memory right now).

I am looking to add a 240V air compressor (rated at 15A) as well as an electric kitchen range to the garage. The garage also does not have enough receptacles. There are walls in the garage that do not have any outlets on them at all, and the walls that have outlets often have only 1 outlet. And my garage is 16' wide x 50' deep with a dividing wall in the middle (2 spaces that are 16'x25' each).

For sure, I want to add the extra receptacle circuits to the garage sub panel. My intent was to also add the electric range & air compressor circuits to the sub panel as well. I guess that all depends on my load calculations though.

Is there a good resource for determining what size breaker and what gauge/type of wire I need to run for my sub panel. I need to see if the existing 40 amp circuit is adequate or if I need to increase that.
 
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Old 06-25-13, 02:59 PM
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The existing circuit is adequate only for a dedicated range circuit at most. If the manufacturer of the range recomend a 40 amp circuit I'd use the existing wiring to the subpanel as the range circuit. Then run a 50 amp #6 circuit for the new subpanel.

Assumes a four wire feed to the existing panel.
 
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Old 06-25-13, 03:10 PM
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Just FYI...

The range going in the garage was from my kitchen (we got a new range in the kitchen), and was run off of a 40A circuit to begin with.

I have been thinking of running the garage range off the main panel and seeing what that does for me. I didn't think about using the existing sub panel feeder wires for the range. I will have to consider that.

Is there a good resource for performing sub panel load calculations?

I have the Black & Decker book "The complete Guide to Home Wiring" & was looking at their load calculation information. That book has a formula sheet for calculating service panel loads. I think it said take the gross load (it explains how to calculate that in the book) and multiply by 1.25 to get the minimum breaker size for the breaker.
 
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Old 06-25-13, 03:21 PM
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Doing a load calculation is always a good idea. My suggestion was a "gut" calculation.
 
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Old 06-25-13, 04:52 PM
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s there a good resource for performing sub panel load calculations?
Here's an Excel template you can plug your information into, from one of the gurus in the field: Residential Load Calculations - Mike Holt Enterprises
 
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Old 06-26-13, 04:05 PM
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One question, is the garage attached or freestanding? If it's freestanding, it can only be fed by one circuit per code. That would mean you couldn't use the existing wiring to the subpanel for the range. You would have to run a new larger feeder to the new subpanel and run everything off of it.
 
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Old 06-26-13, 04:41 PM
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Msradell, good thing to always consider but the title says attached.
 
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Old 06-26-13, 06:04 PM
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Yep, the garage is attached. The front half of the garage is the original attached single car garage that was built with the house. About 16 years ago, the previous owners built another one car garage off the back of the original garage that goes back to the alley. All the circuits in the back garage are fed off of the sub panel. The original garage is mostly fed with circuits from the main panel with the exception of one dedicated circuit for a garage freezer and my soon to be connected air compressor.
 
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Old 06-29-13, 06:17 PM
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New panel installed

I installed the panel today. I used the existing wiring for the sub panel on the with a 40 amp breaker in the main box. I think I can update it later. But my plan is to just make a new continuous wire run from the main panel to the oven when I go to hook that up.

Here are some pics. Let me know if I need to tweak anything.
 
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Old 06-29-13, 06:44 PM
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I would secure the cables on the left closer to the panel. Before they pass the top of the panel box. Otherwise it looks pretty good.
 
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Old 06-29-13, 07:29 PM
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Yep. I tacked them to the plywood board right after I took the pictures.

I installed the panel inverted because the wires came in from the bottom. It made more sense to have the main breaker at the bottom then at the top.

My old panel had all the neutrals and grounds on the same bar. It also had a couple 30 amp breakers with 12 awg wire attached to them. All the white cable in the photo is actually 12 awg wire, it just isn't yellow like today's wire.
 
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Old 06-29-13, 08:07 PM
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I installed the panel inverted because the wires came in from the bottom. It made more sense to have the main breaker at the bottom then at the top.
I figured you were doing your head stands when you mounted it.
 
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