Best way to wire porch light string to porch light
May 22, 2021 7:12 PM   Subscribe

I have a hundred feet of patio string light that I currently turn on but plugging into an outdoor receptacle. I'd prefer they come on when I turn on my hard-wired porch light (which is already at the right elevation on my exterior wall). I was thinking about adding a watertight cord grip to the octagon box behind the porch light, and cutting a short (1ft) length of outdoor extension cord to pass through it. The patio string light would plug into the dangling extension cord socket. You are not my electrician, I know, but is there anything wrong with this plan?
posted by Popular Ethics to Home & Garden (12 answers total) 2 users marked this as a favorite
I think the most important issue is strain relief; you don't want the cord getting yanked or sliced on the edge of the octagon box. Also make sure the string light is not depending on the plug for support.
posted by nickggully at 7:22 PM on May 22, 2021 [1 favorite]

They make adaptors that screw into a light socket and add a plug, the bulb is then one socket's worth farther out.
posted by Oyéah at 7:40 PM on May 22, 2021 [10 favorites]

^^^^Thats how I have my porch lights.
posted by kevinbelt at 8:22 PM on May 22, 2021 [1 favorite]

I recently picked up a few porch lights that have outlets on the side. Here's one of them at Home Depot.
posted by Nonsteroidal Anti-Inflammatory Drug at 8:57 PM on May 22, 2021 [1 favorite]

Response by poster: Oh I forgot to mention - I already have an eyebolt stuck into the wall to provide strain relief for the string lights. For the plug, I'm mostly just worried about water ingress and electrical code requirements - like will a regular Nema 5-15 extension cord be fine, or would it have to be a twist lock connector, or encased in some waterproof housing?
[edit] - seeing the HD product NAID linked, I might want to add a GFCI breaker to this circuit
posted by Popular Ethics at 9:02 PM on May 22, 2021

IANAelectrician, but I don't think splicing a cut extension cord into building wiring is kosher. Like, it can work and provide electricity to your string lights, but it's not going to be to code.

You really want a proper outlet to plug your string lights into. In addition to the adapters and the light fixtures w/ outlets mentioned above, you could add a second electrical box right next to the existing octagon box. The new box could then have an outlet (yes, GFCI if this is outside) with a weatherproof "in-use" cover ("in-use" means it can still be weatherproof when something is plugged in to it).

The fixture linked above doesn't have an in-use cover for the outlets, it looks like. The cover is only protecting the outlets from water if it is completely closed with nothing plugged in. If this is going somewhere where rain might hit it and you will leave the string lights plugged in always, you probably need/want an in-use cover over an outlet.
posted by whatnotever at 9:47 PM on May 22, 2021 [10 favorites]

Best answer: NFPA 70 (NEC) 400.12 specifically prohibits flexible cord from being used "as a substitute for the fixed wiring of a structure", except in specific cases. "Wiring of luminaires" is permitted, but you would be creating a receptacle, which is not. Generally, NEC also requires devices to be listed for their specific use, and even if there were a listing for what you want to do, no extension cord manufacturer is going to do the testing to list their cord to be chopped in half and dangled out the side of a junction box. I can't imagine any inspector who notices your setup will accept it.

Seconding whatnotever on the idea to add a new outlet with an in-use cover next to the light. You can probably add a weatherproof extension ring between your existing junction box and the light, and then run a very short bit of outdoor rated conduit to connect to a new surface-mounted junction box. I can't find any extension rings for octagon boxes, but the linked ring looks likely to seal with an octagon box. Or if your existing box is already on the surface, you could just add the conduit to that box instead.

When you wire the outlet, just wire it to the same wires as the light, and it will also be switched. It will need to be a GFCI outlet, unless the lights area already on a GFCI breaker.
posted by yuwtze at 10:36 PM on May 22, 2021 [6 favorites]

I use something similar to this gadget. The switch is mounted on the wall just inside my back patio door with double sided tape, and the little receiver thing is spliced into the outdoor lights. I've had this (it's not this exact one, but a similar model) for a couple of years now without issue. Works just like a regular light switch.
posted by newpotato at 2:44 AM on May 23, 2021

There are correct ways to do this. Wiring extension cord directly into a fixture box is not to code in any jurisdiction. Dangling extension cord sockets sounds like a great way to invite arcing when the wind moves it enough to unplug. Contact an electrician.
posted by Geckwoistmeinauto at 4:34 AM on May 23, 2021 [1 favorite]

Response by poster: Thanks for the advice everyone. I wanted to avoid a second junction box (in favour of an extension cord) because the normal arrangement would be huge and ugly against the side of my brick house. But the code is the code. (I assume the Ontario Electrical Code has a similar rule - can't check because it isn't publically available, grrr.)

I will spend some time looking for a lower profile outdoor junction box or maybe something that has outlets on the side per NAID's link. Whatever I chose I'll run it by an electrician, as advised.
posted by Popular Ethics at 9:56 AM on May 23, 2021

Ontario code also prohibits flexible cord for permanent wiring.

It's not impossible to chip the mortor out from a couple bricks next to your light, create a cavity in the wall to access your current wiring and/or box, install a new outlet for your string lights and then reinstall the brick.

Arlington makes a slick in use box with cover for brick that ends up being nearly flush with the wall even when in use .

There are also several ways to control your current outlet wirelessly.
posted by Mitheral at 10:26 AM on May 23, 2021 [1 favorite]

Response by poster: It's a double brick century home and I have zero interest in carving out a cavity in the brick for a flush mount receptacle. It's unfortunate that a surface mount weatherproof box > in use cover combo ends up being over 4" thick.
posted by Popular Ethics at 10:47 AM on May 23, 2021

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