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My city adheres to the 2008 NEC. I've got a run of outlets around a basement room on one circuit. On an exterior wall I've got a weatherproof outlet that's on a different circuit and somewhere in between two of the interior circuits. Is it within code to remove that exterior outlet from its current circuit and "branch" it off the interior circuit? I thought I remembered hearing once that there are limitations to branching circuits.

Additionally, are there any specific code requirements pertaining to exterior outlets that I should be aware of?

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From my experience in building we had to keep to 3 plugs per branch (2.5mm solid core) and we never mixed outside ones with internal ones. But this was in South Africa where all heating was electric. In EU mostly this could be slightly slacked as there is Gas/Coal heating. In USA - no idea. –  ppumkin Jul 18 '11 at 13:48

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The outdoor receptacle will have to be GFCI protected.

NEC 210.8 At dwellings, ground-fault circuit-interrupter (GFCI) protection shall be provided for all receptacle outlets installed in bathrooms, garages, grade-level portions of unfinished accessory buildings, crawl spaces, unfinished basements, kitchen countertops, wet-bar sinks, boathouses and outdoors. Receptacles that are not readily accessible may be exempt from the GFCI requirement

The receptacle will also have to be contained in a weatherproof enclosure, and if something will be plugged in for extended periods (Christmas lights for example) the enclosure should be labeled as "watertight while in use".

NEC 406.8 15 and 20 amp, 125 and 250 volt receptacles installed outdoors in a wet location shall have an enclosure that is weatherproof whether or not the attachment plug is inserted

It should not be a problem branching from an interior circuit, but you'll want to seal the hole where the cable enters the house to prevent moisture from entering.

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Tester has it right, I just wanted to add one more caveat from the NEC. Regardless of compliance with any other rule, you cannot, under any circumstances, use the "kitchen appliance branch" circuits to feed an exterior outlet. The "appliance branches" are the two 20-amp circuits powering your countertop outlets (and possibly other things depending on the year the house was built). –  KeithS Jul 29 '11 at 19:20

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