A sealed outdoor enclosure on a pole or post needs 120 V AC in, 5 V and 12 V DC out, and a safety ground that actually works. The short answer: land the mains through listed fittings into a box rated for the job, bond the ground to the metal, and keep the AC section separated from the low-voltage wiring. Or keep the AC out of your enclosure entirely and bring only DC through a gland. Both are legitimate; pick one and do it cleanly. This article walks through both paths. The enclosures we build are rated NEMA 4X / IP66 by the manufacturer; not UL listed.
Two safe ways to feed the box
Path A: mains inside. The 120 V hot, neutral and ground enter through a listed fitting or short conduit run, terminate on a listed power supply or a small breaker block inside, and the DC side feeds your electronics. This is how most industrial panels work. It demands a gasketed, outdoor-rated enclosure, listed terminations, and separation between AC and DC wiring.
Path B: mains outside. A listed, outdoor-rated power supply or LED driver sits in its own listed enclosure at the base of the pole, permanently connected to the branch circuit. Only its 12 V DC output travels up through a gland into your enclosure, where a small buck converter makes the 5 V rail. Your enclosure then contains nothing above low voltage.
Path B is usually the better choice for a small sensor suite. It removes the AC hazard from the box you open most often, and it leaves you with one gland to seal instead of a conduit penetration. The pole mount enclosure for outdoor electronics guide covers the mounting side of the same install.
What the code expects, in plain words
The National Electrical Code treats 120 V branch-circuit wiring as premises wiring: it belongs in listed boxes and enclosures, terminated on listed devices, protected by a listed overcurrent device. A sealed electronics box is not automatically a listed wiring enclosure just because it is waterproof. In US installations, NEC 110.28 also ties the enclosure type marking to the environment, and the NEC's Table 110.28 matches enclosure types to locations. If your inspector wants a listed enclosure for the AC section, believe them.
The equipment grounding conductor that runs with the circuit is sized from the rating of the overcurrent device ahead of it, using NEC Table 250.122. Insulated grounding conductors of 6 AWG and smaller must be green or green with yellow stripes under NEC 250.119. And the earth is not an effective ground-fault current path under NEC 250.4(A)(5), so the ground rod beside the pole is at best an auxiliary electrode under NEC 250.54, never a substitute for the grounding conductor.
The grounding and bonding guide works through sizing and bonding in more depth.
Path A: power supply inside the enclosure
What you need: an outdoor-rated enclosure big enough for the supply plus the electronics, a listed power supply rated for the environment, a listed gland or conduit fitting for the AC entry, a ground lug, and ring terminals.
- Size the box first. Add the supply's heat dissipation, typically 10 to 20 percent of its output power, to the electronics load, then check the temperature rise. The PCB heat in a sealed enclosure article shows the arithmetic.
- Bring the AC in at the bottom, through a listed fitting sized for the cable. Follow the cable gland installation steps so the entry keeps its rating. Never mount a gland facing up where water can pool on it.
- Terminate hot and neutral on the supply's line terminals. Nothing else lands on those terminals.
- Land the equipment grounding conductor on a listed lug bonded to the enclosure's metal. On a plastic-body box, bond the metal frame; scrape coatings at the contact point, because NEC 250.12 requires paint and enamel removed from grounding contact surfaces unless the fitting makes removal unnecessary.
- Run the DC output on the other side of the backplate, away from the AC wiring. Keep AC and DC separated the whole way; never bundle them in the same duct.
- Add a drip loop on the outside of the entry so water running down the cable drips off below the gland, as the outdoor junction box sealing article describes.
A 6 x 6 x 4 in enclosure fits a small supply and a sensor interface board; anything with a breaker or room to work wants an 8 x 6 x 4 in box or larger.
Path B: driver outside, DC only inside
What you need: a listed driver or power supply rated for outdoor installation and permanent connection, a listed enclosure for it, and one gland on your electronics box.
- Mount the driver's enclosure at a serviceable height on the pole, with its entries pointing down.
- Terminate the branch-circuit hot, neutral and ground inside it on the driver's line side. Bond the ground to that enclosure if it is metal.
- Route the DC output up the pole and through a gland in the bottom of your enclosure. Leave a drip loop outside.
- Inside, feed the 12 V loads directly and a small buck converter for the 5 V rail. Give the converter a fuse or a supply with current limiting.
- Check voltage drop on the DC run: for a 12 V feed over 30 ft, keep the current low or step up the wire gauge, because a few tenths of a volt matter at the far end.
Your enclosure now holds only Class 2-style low-voltage wiring, and the seal question is one gland done right.
The safety-ground question
A plastic enclosure with a metal frame still needs the frame bonded if any metal part could become energized by a fault. Bonding means a listed lug, star washers or a scraped-bare surface, and hardware that will not loosen with vibration. Under NEC 250.96(A), metal parts serving as equipment grounding conductors, including enclosures, must be bonded together so they can safely carry any fault current imposed on them.
If everything inside the box runs from a listed, Class 2-rated supply whose output is isolated from the mains, there may be nothing at line potential inside to bond. The ground still follows the AC wiring to wherever the supply lives. In Path B, that is the driver's enclosure, not yours.
Checks when you are done
- Measure continuity from the pole's grounding conductor to the bonded metal frame. It should be near zero ohms.
- Verify the supply output under full load, at the far end of the DC run, not at the terminals.
- Hose-test the gland and door area, then open the box and look for tracks of water. Do it before the electronics go in.
- Confirm the AC entry would shed water: entries at the bottom, drip loops below every gland.
Mistakes that cost the rating or the safety
Drilling an oversized hole and filling it with sealant is the classic one; a gland seals only against its own rated hole size. Splitting one gland between the DC pair and an antenna feed, which the two cables through one gland article covers, is another. Inside the box, the costly mistakes are landing the ground under painted metal, running AC and DC in the same duct, and sizing the box without the supply's heat. If you need a size or cutout pattern the catalog does not carry, custom enclosures are built to your drawing and delivered in 10 business days, counted from your approval of the drawing. The enclosure selector narrows the catalog sizes by environment and inside dimensions.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 6 × 6 × 4 in | 304 stainless | 6 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 8 × 6 × 4 in | 304 stainless | 8 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can I run 120 V wires straight into my sealed enclosure through a cable gland?
Only if the gland and the enclosure are both acceptable for that use. A gland listed for DC and signal cables is not automatically suitable as the sole support and seal for premises wiring at 120 V. In practice, feed the box through a short length of listed conduit with listed fittings, or land the mains in a listed junction box and take a listed cord or DC leads from there. Any hole you drill must keep the enclosure's rating, so check the gland installation guide before cutting.
What do I do with the safety ground in a plastic enclosure with a metal frame?
Bond the equipment grounding conductor to every metal part that could ever be energized by a fault, including the metal frame, using a listed lug and hardware that bites through coatings. Under NEC 250.12, paint and similar coatings must be removed from contact surfaces at grounding connections unless the fitting is designed to make that unnecessary. The earth itself is not an effective ground-fault current path under NEC 250.4(A)(5), so a ground rod never replaces the equipment grounding conductor that runs back with the circuit.
Is it safer to keep the AC outside and bring only DC into the box?
Often yes, for small sensor loads. A listed, outdoor-rated power supply or driver in its own listed enclosure takes the AC terminations out of your box, and only low-voltage DC passes through a gland. You lose one potential leak point instead of gaining a conduit penetration, and anyone opening your enclosure later is not facing 120 V. The trade-off is one more enclosure on the pole and a slightly longer DC run with voltage drop to check.
Does adding a power supply inside the box change the enclosure size I need?
It can. A power supply wastes 10 to 20 percent of its output as heat, and a sealed box holds that heat. Add the dissipation of every part, then check the internal temperature rise against the electronics' ratings, as the PCB heat in a sealed enclosure article explains. A 6 x 6 x 4 in box suits a few watts; a supply feeding several sensors usually wants the next size up.
