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Old 09-19-2011, 09:49 PM   #1
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sub panels wired in series?


I need to run electrical to 2 out buildings. How everything is positioned, it would save me from buying an extra 60' of wire or more if I run the garage panel from the shed vs. running them both from the main. Any reason I can't run both sub-panels on 1 line? I have a shed I would one day like to put a kiln in and a garage I'd like to be able to weld in. both are high draw items, but I would be fine not running them at the same time (that would probably trip my main if I tried it anyways)

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Old 09-19-2011, 11:36 PM   #2
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sub panels wired in series?


A little clarification... you plan on running the main heavy gauge line from the main panel to the garage, then go from the garage to the shed with a smaller gauge line? There's no reason to go to the shed from the main if you can branch off the garage.

The easiest way I see to do it is run a big enough feeder line to power the garage and shed from the main to the garage (in conduit), into a subpanel. Make a branch of the subpanel go to the shed, into another (smaller) subpanel. Everything should be run in conduit, so you can always upgrade to something heavier down the road.

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Old 09-20-2011, 08:03 AM   #3
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sub panels wired in series?


It is perfectly okay to daisy chain subpanels, i.e. have a "sub-subpanel".

Do a load calculation as suggested by the National Electric Code book and also list the appliances (including welder and kiln) you plan to use, and use the larger of the wire sizes you come up with.
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Last edited by AllanJ; 09-20-2011 at 08:09 AM.
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Old 09-20-2011, 10:06 AM   #4
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sub panels wired in series?


Here is the plan in a little more detail;

Run from the basement of the house to the basement of the shed (used to be a chicken coop with a hidden still underneath), leave a big loop, then out to the garage were I'd put the garage sub panel.

After the shed is rebuilt (next major project, next summer I hope) cut the loop and install the sub in the shed between the garage and the house.

The welder and the kiln would probably each need 50 amp circuits (haven't got a kiln yet, plan ordering the welder today, a Millermatic 252)

My initial plan is 100 amp lines and 100 amp boxes. 60 amp boxes would not leave me much room for lights and outlets.
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Old 09-20-2011, 11:05 AM   #5
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sub panels wired in series?


What size is the service coming into your house?

You might want to run larger than 100Amp to your first subpanel.
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Old 09-20-2011, 05:14 PM   #6
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sub panels wired in series?


Make sure you calcuate the voltage drop for the distance to the garage. 100 amp wire itself is expensive and over any real distance you'll need an even larger wire and it'll get super expensive.
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Old 09-20-2011, 08:52 PM   #7
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sub panels wired in series?


I am not too worried about voltage drop in the garage. The welder has a pretty wide voltage range, plus I've got pretty good power here compared to other places I have lived. Worst case I can see is my cordless tools might not charge if I am running the welder.

I could do heavier gauge to the shed. I have thought about it, but there are downsides beyond just the financial. I'd have to install a box now and risk it getting damaged during the demo (demo will probably involve a cable and a 4x4). I think just the wire on its own will be much more likely to escape harm. Then you also have to consider we are talking some pretty serious gauge at that point too in Aluminum (copper wire is just plain not an option at these prices) making working with it not much fun. I upped the gauge on a previous sub-panel I did, but that was more than a 400' run. This will be well under half that to the far panel.

One more question; is there any reason I can't down gauge the neutral since I will not be using it much as my major loads are all going to be 240volt? beyond a light and outlet circuit in each building, everything else I can think of will be 240 volt. Now that I think of it, any sub panel should be able to drop it a couple of sizes safely. Even if it had a bunch of 120v heavy use circuits, they would not all be on the same leg unless an effort to to screw it up intentionally.

Last edited by forresth; 09-20-2011 at 09:10 PM.
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Old 09-20-2011, 09:24 PM   #8
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sub panels wired in series?


I don't think you understand what voltage drop is. The longer a wire is, the more voltage you loose due to resistance (impedance maybe?). So the further a wire run is the bigger gauge it needs to be to compensate for this.

I'm not sure if reducing the size of the neutral is in the code or not but it's not a good idea. If you are running 220v I believe you can make the neutral 70% the size of the 2 legs.
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Old 09-20-2011, 09:58 PM   #9
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sub panels wired in series?


Quote:
Originally Posted by matt151617 View Post
I don't think you understand what voltage drop is. The longer a wire is, the more voltage you loose due to resistance (impedance maybe?). So the further a wire run is the bigger gauge it needs to be to compensate for this.

I'm not sure if reducing the size of the neutral is in the code or not but it's not a good idea. If you are running 220v I believe you can make the neutral 70% the size of the 2 legs.
I know what voltage drop is. I am not worried about it. There is currently a single 20 amp circuit running to both buildings on a 12 gauge wire, and that was fine until the wire was damaged during a chain link fence install. I would have just rerouted that line, save for the welder.
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Old 09-20-2011, 10:59 PM   #10
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sub panels wired in series?


Sorry, I misread your post about the voltage drop.

What size conductor do you plan to run? You'll have to go with 2/0 AL if you ever plan on using all 100 amps at once. With the 70% calculated, your neutral could be 2 gauge at the smallest.

As far as your ground, your probably required by code to attach it to ground rods next to the garage and shed. Anyways, it's easier than running a ground wire back the whole way.
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Old 09-20-2011, 11:34 PM   #11
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sub panels wired in series?


Ground rods do NOT replace an equipmnent ground being run back to the panel. They serve completely different purposes (lightning vs. ground fault).

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