I am planning to add some devices/receptacles to a 20amp circuit in my house. The following image shows the original circuit and my proposed additions. I'm specifically concerned about my plan for wiring outlets after the GFCI tester (see items 12 thru 17 in the image). Three outlets will be wired in parallel from a junction box directly after the GFCI tester, with two additional outlets wired in series off of one of those paralleled outlets. Are there any problems with this plan? Any input or confirmation is much appreciated. Thanks! Old vs New Circuit Diagram

  • 4
    None of your outlets will be wired in series. That's not how house wiring is done. They may be in a series on various circuit branches, but they're always connected in parallel. If this doesn't make sense you might seek expert local help.
    – isherwood
    Sep 2, 2020 at 16:19
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    What kind of outlets are these? Or rather, how many on this circuit will be receptacle outlets (as opposed to hardwired outlets such as lights)? If >12, we'll need to know which state you are in. Will any of these receptacle outlets serve a kitchen, bathroom or laundry room? Sep 2, 2020 at 16:19
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    Just duplex outlets (not GFCI) after the blank GFCI tester. These new outlets will all be along the soffit of my house. Intent is to use them for Christmas lights.
    – Dave F
    Sep 2, 2020 at 16:24
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    Here is the "blank GFCI tester" I refer to. The intent is that this provides GFCI protection to all of the new outlets I'll place along the soffit of my house, while being easily accessible. link
    – Dave F
    Sep 2, 2020 at 16:54
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    Also you may want to revisit "series" vs "parallel", those have very specific meanings in electrical. Best to stick to plain English and avoid the jargon unless you have strong command of it. Sep 2, 2020 at 17:59

1 Answer 1


Electrical cable/conduit routing must be tree topology

You can also wire things in a "vine" topology, like 12-15-16-17 - after all, a vine is a type of tree.

You can also wire in a star topology (like 12-9-15-14-13). That counts as tree topology also. (but with many connections, box fill rules must be followed just like anywhere else).

You can freely mix them all.

Here's the acid test: In your graphics editor, take your cabling diagram (remove the non-cablng elements like gray walls). Now, grab the paint can tool, and pour purple color anywhere on the diagram. Does it fill the whole diagram? Then you have tree topology. Yours appears to pass.

  • The other way of thinking "series" vs. "parallel" would be: parallel = normal wiring of all hots together, all neutral together and series = hot into receptacle, output (which should be neutral) as hot into next receptacle, etc. then all coming back on one neutral from the end. Which would (a) not work at all when any one receptacle is empty and (b) have major problems when everything is plugged in. Sep 2, 2020 at 18:36
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    @manassehkatz your way sounds like the actual meaning of the words. Sep 2, 2020 at 19:57
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    I see. I was erroneously using "series" to describe wiring from load terminals of outlet 15 to line terminals of outlet 16, and again from 16 load to 17 line (I think this is also referred to as daisy chaining). And I thought "parallel" was the correct term referring to the fact that the lines for outlets 13, 14, and 15 are all wire nutted together with the same positive wire in j-box 12 (and the same for their neutrals, too). Thanks for explaining my misused terminology.
    – Dave F
    Sep 2, 2020 at 20:48

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