Short answer: your fixture is its own junction box when its wiring compartment is part of its listing. The instruction sheet draws the connections inside the cavity behind the mounting plate, and the label on your compartment says so. Without that, the plate is a mounting bracket, and the feed lands in a box behind it: a 4 in [102 mm] round pancake, 1/2 in [13 mm] deep, stamped 6.0 cu in inside — room for exactly one 14/2 feed with ground. Here is the two-minute check, the box arithmetic, and where the splices go when the wiring grows.
What a splice-compartment listing covers
A luminaire listed to UL 1598 is evaluated with the wiring compartment it ships with. The knockouts, the strain relief and the splices you make inside that cavity are covered by the listing. The recessed can light is the familiar case: the small box clipped to the housing is listed as a splicing enclosure, and its label states the conductor temperature and how many conductors it holds. A surface floodlight whose backplate forms a wiring cavity works the same way when the instructions show the feed landing there. Those instructions are part of the listing — the NEC has listed equipment installed according to the listing and the sheet that comes with it. The wiring diagram, not the shape of the plate, settles which case you have.
The two-minute check on your fixture
Open the breaker and prove the circuit dead with a meter before you take anything off the wall. Then work through four questions:
- Where does the diagram put the connections? Drawn inside the fixture cavity, the compartment is the box. A round box drawn behind the plate means your fixture mounts on a box.
- What is stamped or molded on the compartment? A splicing-enclosure marking or "suitable for through wiring" adds conductors beyond the feed. "Supply conductors 90 C minimum" is the usual temperature line on LED floods — check your existing cable against it.
- Which cable does the sheet name? UF-B for a direct outdoor run, THWN in conduit; the compartment is evaluated for the types it lists.
- How many cables arrive? One feed in, fixture leads out. A second cable turns the compartment into a junction serving other loads, and a junction needs its own box.
If the wall has no box at all today, the run-up to this decision is covered in mounting an outdoor fixture with no junction box in the wall.
Why the IP65 on the sales page settles nothing
The online listing says IP65, which sounds decisive and is not, for a US install. NEC 110.28 makes the enclosure type marking the rating that counts for equipment rated 1000 V or less in the locations Table 110.28 covers. An IP code alone will not satisfy it. On a luminaire, the phrase that carries the weight is "Suitable for Wet Locations" on the label, beside the mark of the testing laboratory that listed the fixture. Your outdoor floodlight carries both. The box you add behind it is marked for wet locations too, and outdoor boxes carry a type marking such as 3R. Treat the IP code as a bonus line for international specs, with the type marking as the one that counts.
When the plate cannot be the junction box
Four situations push you off the fixture compartment, and each ends in a box:
- The sheet shows a round box behind the plate, or the fixture carries no splicing marking.
- More than one cable arrives: a second floodlight teed off, a photocell, a switch leg. Those splices serve other loads, and the NEC puts every splice in a box that stays reachable without breaking the wall finish.
- The compartment label sets a conductor count or a conductor temperature your feed exceeds.
- There is no sheet and no label, so the cavity gives you nothing to install to.
A box behind the plate stays accessible as long as you can reach it by unscrewing the fixture.
The box behind the plate, with the arithmetic
Take the common case: one 14/2 UF-B feed with ground running to a twin-head floodlight on wood siding. The round pancake from the short answer — 1/2 in deep, stamped 6.0 cu in — is the box. The NEC box-fill table gives each 14 AWG conductor 2.00 cu in, and the equipment ground counts once at the largest size in the box: 2 x 2.00 + 2.00 = 6.00 cu in. Your pancake holds that single cable exactly, with nothing spare. If the box has an internal cable clamp, the clamp counts as one more conductor and you are over.
Run 12 AWG and the same single cable no longer fits: 2 x 2.25 + 2.25 = 6.75 cu in against 6.0. Step up to a same-size octagon, 1 1/4 in deep and stamped 18 cu in. That leaves 18 - 6.75 = 11.25 cu in of spare, five 12 AWG conductors' worth (5 x 2.25). The photocell leads and a switch leg fit with the cover back on. Leave yourself the NEC's 6 in [150 mm] of free conductor at each box, so the splice folds in and the plate still closes.
Mounting it so water stays out
On combustible siding the NEC wants the box flush with the surface; on noncombustible finishes — stucco, masonry, fiber cement — it may sit back up to 1/4 in [6 mm]. A 3 1/2 in [89 mm] hole saw counterbore takes most of the waste out of clapboard for the pancake; pare to depth so the rim sits flush, and your fixture seals against the box. Use a box listed for wet locations.
Seal the top and sides of the wall penetration with a sealant suited to the wall. Leave the bottom free to drain: NEC 314.15 permits drainage openings of 1/8 in to 1/4 in [3-6 mm] in boxes listed for damp or wet locations, so whatever wicks in leaves. A drip loop below the box keeps running water off the splice — the details are in sealing an outdoor junction box with glands, drip loops and drains and sealing a junction box to a brick wall against running water. Where the hole in the wall is the real problem, covering wall cable entry holes with a weatherproof box is the companion fix.
When the wiring outgrows the fixture
Add a photocell, a second light and maybe a switch, and you are past the octagon. You want a junction box built for outdoors, with glands. A 6 x 6 x 4 in 316L wall-mount enclosure — 6 x 6 x 4 in [152 x 152 x 102 mm] outside — takes a feed, a photocell and two fixture drops with room to spare. It is rated NEMA 4X / IP66 by the manufacturer; not UL listed. Bring the cables in through glands in the bottom wall, rated IP66 or better, because the lowest-rated part sets the assembly's rating.
316L earns its keep on coastal walls and anywhere de-icing salt lands; 304 stainless is the standard grade under an eave. Feed the second light through glands sized to the cable, as the outdoor electrical enclosures guide covers for feeds to exterior fittings. The full size range is in wall-mount enclosures, and custom enclosures take your cutouts from one piece, delivered in 10 business days from your approval of the drawing.
What to specify
| What you are mounting | What carries the splices | The number that decides it |
|---|---|---|
| Sheet draws connections inside the cavity | The fixture's own compartment | One feed only; 90 C conductors where marked |
| Sheet shows a box, or no splicing marking | Round pancake, mounted flush | 6.0 cu in = one 14/2 with ground, exactly |
| 12 AWG feed, or two cables | Octagon, 1 1/4 in deep | 18 cu in; a 12/2 with ground uses 6.75 cu in |
| Photocell, second light, switch leg | 316L wall-mount box with bottom glands | NEMA 4X / IP66 manufacturer rating, as above |
The decision in one line: read the sheet before you drill. A marked compartment with one cable — connect behind the plate. No marking, or a second cable — pancake or octagon, mounted flush and drained. Wiring that has grown into a small distribution point — a 316L box with bottom glands, and every splice still reachable with the door open.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 6 × 6 × 4 in | 316L stainless | 6 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can I feed a second floodlight from the first one's splice compartment?
Only when the compartment is marked 'suitable for through wiring'. The listing covers the fixture's own connection plus the conductors the marking names; an unmarked compartment serves its own feed alone. The junction for a second light goes in a box of its own — an octagon at 18 cu in takes both cables with room to spare — and it stays reachable with the fixture off.
Will a 6.0 cu in pancake box take 12/2 cable with ground?
No. The NEC box-fill table gives 2.25 cu in per 12 AWG conductor, and the ground counts once more: 2 x 2.25 + 2.25 = 6.75 cu in against the box's 6.0. The same cable in 14 AWG needs 2 x 2.00 + 2.00 = 6.00 cu in — exactly full. Run 12 AWG into an octagon 1 1/4 in deep stamped 18 cu in.
Should I seal the pancake box to the wall all the way round?
Seal the top and sides and leave the bottom open. NEC 314.15 permits drainage openings of 1/8 in to 1/4 in [3-6 mm] in boxes listed for damp or wet locations, so condensation and wind-driven water that gets in leaves instead of pooling behind the fixture.
What marking proves the fixture itself is rated for outdoors?
The label reads 'Suitable for Wet Locations', beside the mark of the testing laboratory that listed the luminaire. That is the phrase a US inspection looks for; under NEC 110.28 the enclosure type marking is the rating that counts, and an IP65 line on the sales page is not its equal. The splicing or through-wiring marking is a separate line on the same label.
The fixture came with no instruction sheet. Can I still splice behind the plate?
Treat the plate as a mounting bracket. Without the sheet or a marking you have no listing to install to, so land the feed in a box: a pancake, recessed flush, for a single 14/2 cable; an 18 cu in octagon for 12 AWG or a second cable. Replacement sheets come from the fixture maker.
