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I'm looking to add an outdoor outlet to the back of my house. There's an existing UF cable line that runs from the exterior basement wall to the exterior first floor wall, entering directly behind a large switch panel that controls the first floor lights. I assume this is an unswitched line carrying power to that panel.

Can I add an outlet to this line? Is it safe/can it be waterproofed to cut the line, then connect the two ends inside a junction box?

Obviously, I'm tempted to add an outlet directly to the line (that is, have an outlet sitting in the junction box where I splice). I've read this is against code, and I'll need to run more cable to a separate outlet. Is this correct?

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    One trouble with cutting the cable to insert an outlet is that you'll need to bring at least 8 inches of slack (10+ is better) to the place where the new box is to be installed, or else use two boxes so that additional cable can be spliced in. Is there enough slack available somewhere along the cable, and can the slack be moved into the right place? Pictures may help us understand your context better. – Greg Hill Nov 4 '19 at 20:39
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    If you've read that this is against code, you should share why. Maybe there's more to the story than what you've told us. Does the cable run outside? Why is it UF? – isherwood Nov 4 '19 at 20:42
  • The wording large switch panel has my interest peaked is this a sub panel as I guessed in my answer? If this cable is protected by more than a 20 amp breaker it will take a bit more work to make it happen. – Ed Beal Nov 4 '19 at 21:53
  • Can you post a photo of the switch panel? It may be simpler to tap power there, fill permitting... – ThreePhaseEel Nov 5 '19 at 0:47
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It depends on the size of the cable/ breaker size going up the side of the house. If that cable is protected by a 15 or 20 amp breaker it is possible to splice into the cable, as previously mentioned you do need additional wire length 1 foot minimum. you need 6” on the supply and 6” on the run upstairs to have enough slack. With that cable running from basement to the upper floor it needs to be protected up to 8’ above ground in most cases So that needs to be done correctly

if you add a box and WR rated GFCI with a extreme duty or in use cover. UF wire is usually protected from UV but below 8’ requires conduit for protection and some locations all the way back into the house requires conduit.

If the breaker is larger than 20 amp it cannot be done without adding a sub panel, And breaker as taping into a large feeder would require.

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GFCI

All this should be OK - given constraints of sufficient slack in the cable, etc. But if the circuit is not already GFCI protected at the breaker or some other location prior to the new outdoor location, then you need to either:

  • Install a GFCI-protected receptacle in the outdoor location

or

  • Install GFCI protection in the breaker panel (replace the regular breaker with a GFCI breaker) or splice in GFCI protection somewhere before the outdoor location
  • Although a GFCI in the panel would work it would be a bit nuts something upstairs trips now all the way to the basement to reset the GFCI . If a 15 or 20 amp circuit I would tap the line and not use the load at all on a GFCI outlet. Anything that needs GFCI protection can be protected upstairs. – Ed Beal Nov 4 '19 at 21:49
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    @edbeal that will often save money too, but GFCI trips occur too infrequently to care about the long walk. An appliance only gets 3 strikes, first natural trip, second confirm trip, third in the kitchen to confirm the problem moves, and into the trash it goes. – Harper - Reinstate Monica Nov 4 '19 at 22:43
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This should be fine. A couple caveats:

  • You'll need at least a foot of slack. One trick is to use two junction boxes--the first to extend the cable, adding slack, and the second for the outlet. Think it through before you cut so you don't end up short anyway. All junction boxes need to remain accessible (not buried behind drywall).
  • Use pigtails rather than receptacle passthrough (or, worse, the backstab ports). You don't want to run a potentially heavy current between the same-side screws on an outlet if you can help it. Doing so adds extra points of failure for the downstream portion of the circuit. Bring the source wire, the downstream wire, and a jumper for the outlet together in a suitable connector, such as a yellow or red nut.
  • Use a large enough box for the outlet and those pigtail connections. A full-depth (17 c.i.?) single-gang box would be fine.

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