Short answer: land the portable power cable straight in the shore sub-panel; NEC Article 555 sets no shore-side junction box. You need two things at that landing: terminals that hold the cable's fine stranding, and a gland that grips the jacket. Flexible strand classes run up to K and M, beyond the Class B stranding a standard lug is evaluated with. Put the junction box at the dock end, where the feed splits to the power posts, mounted above the datum plane 30 in [762 mm] above the water. On shore, use a Type 4X 316L stainless enclosure; rainproof Type 3R only survives inside a dry, covered room.
The run from the shore panel to the posts
One cable serves the whole trip. The marina rules in Article 555 call for extra-hard usage portable power cable, rated at least 600 V and 75 °C [167 °F], listed for wet locations, sunlight resistant, with the outer jacket unbroken end to end. State amendments, like Washington's marina rules, spell out the same cable requirements. The cable leaves your shore sub-panel, crosses the gangway and lands at the power posts on the floats.
The panel size does not change the landing. Whether the shore service is 100 A or the 600 A of a large marina feed, the portable cable terminates on the panel's lugs or in its terminal gutter, whichever your panel gives you. A shore-side junction box enters the picture in three cases: the panel has no terminals suitable for the strand class, the feed splits toward several floats, or the gutter leaves no room for the cable's bends.
At the dock end you do want a box, because each power post needs terminations under a gasketed lid and above the deck. Where the run crosses the gangway, sleeve it in flexible conduit with a wet-location fitting; the wet-location flex conduit connector article covers which fitting keeps its seal while the gangway moves.
Match the terminal to the strand class
Portable cable earns its flexibility from fine stranding. NEMA's bulletin on fine-stranded connections lists the common fine classes as G, H, I, K and M, with K and M the finest, and a marina cable carries one of them. Class B building wire, the stranding most lugs are evaluated with, is 7 strands from 8 to 2 AWG and 19 strands from 1 to 4/0 AWG. A fine strand pack under a Class B set screw touches at a few line points, runs hot and works loose.
Three fixes hold, in order of preference:
- Terminals marked for fine-stranded conductors: breakers, terminal blocks and lugs the maker evaluates with the fine classes.
- A crimped wire ferrule, which turns the strand pack into a solid-like pin that a standard screw grip holds; selecting wire ferrules for fine-stranded conductors page covers sizing and crimp tooling.
- Pin sleeves or pin adapters into the terminal block, the way marina crews terminate seasonal cord sets.
Torque each termination to the value printed on the terminal label, and check the torque again after the first season of heat cycles.
The enclosure rating the shore end needs
A waterside wall takes rain, wave splash, wash-down spray and salt air, and the rating has to cover all four. Type 3R is tested for rain, sleet and ice; it carries no hose-down or splash rating, which is why many shore panels rust through within a few seasons. Type 4X adds the hose-down test and a corrosion test: NEMA 250 gives Type 4X enclosures 200 hours of salt spray alongside a 304 stainless specimen. The Type 3R vs Type 4 guide breaks the tests down line by line, and the outdoor enclosures guide covers sun, ice and wash-down in one place.
Material decides the corrosion fight. Chlorides pit 304 at room temperature under deposits and in gasket crevices, so salt air eats a 304 box from the outside in. The molybdenum in 316L raises pitting and crevice resistance, which makes it the waterside grade.
Keep the NEMA type in your specification even when an IP code appears next to it. NEC 110.28 states in US installations that an IP code alone does not replace the enclosure type rating, and NEC Table 110.28 pairs locations with the type numbers. Our wall-mount stainless boxes are rated NEMA 4X / IP66 by the manufacturer; not UL listed. When the shore assembly is a listed industrial control panel, an unlisted enclosure changes how the panel gets accepted; the unlisted enclosure for a listed control panel article walks that path, and the wet location ratings article covers the wiring limits that come with it.
| Location | Rating to order | Material |
|---|---|---|
| Shore wall beside the gangway, open to spray and salt | Type 4X | 316L stainless |
| Covered shore room, no wash-down, no splash | Type 3R | painted steel holds |
| Floating dock deck and power posts | Type 4X | 316L stainless or GRP |
Decide by what actually reaches the box: rain alone gets 3R, anything sprayed gets 4X, anything salty gets 4X in 316L.
Mounting heights above the water
Article 555 measures heights from the electrical datum plane. For a floating pier, the plane sits 30 in [762 mm] above the water level at the pier. Components on the dock go at least 12 in [305 mm] above the deck and never below the plane; fixed wiring on land stays at least 2 ft [610 mm] above the highest water level.
Worked example: a float deck sits 16 in above the water. The deck rule alone puts a box bottom at 16 + 12 = 28 in above the water. That falls short of the datum plane at 30 in, so the plane governs. Mount the bottom 30 in above the water, which is 30 - 16 = 14 in above the deck, and set it at 15 in to keep an inch in hand for tide and load swing.
Shore side, the panel keeps its own clearances. NEC 110.26(A) asks 3 ft (900 mm) of working depth for equipment up to 150 V to ground in Condition 1. It also wants 30 in of width or the equipment width, and a door that opens at least 90 degrees. NEC 240.24(A) caps the highest breaker handle at 2.0 m (6 ft 7 in) above the floor. The enclosure mounting guide covers the wall fixings and the height choices that follow.
Sealing the entries
Every hole you cut is where the rating dies first. Order the gland holes as cutouts on the drawing so the builder cuts and deburrs them with the seal intact; the cutouts and glands guide shows how hole size and position follow the gland. Before any field hole in a Type 4X wall, read screws through a control panel wall and the Type 4 rating, because a fitting in a wrong-sized hole drags the whole box down a rating level.
Size each gland by the jacket, not by the thread. Measure the cable's jacket outside diameter and pick a multi-range gland whose seal range covers it. As an example, a 3-conductor extra-hard cable with a 0.8 in [20 mm] jacket needs a seal range that brackets 0.8 in. In salt air, a stainless or nickel-plated brass body outlasts plain brass. A metallic gland also carries bonding through the stainless wall. NEC 250.96(A) requires the metal parts to be bonded so they can carry any fault current; the cable gland bonding requirements article shows the bonding washer detail.
At the dock end, fit glands pointing down or sideways and leave a drip loop below each entry, so water sheds off the jacket before it reaches the seal. The mounting cable glands facing up article explains why upward entries collect water. For a cord set you unplug each season, the bulkhead gland vs one gland comparison shows which entry stays sealed while the cable is out.
The weakest entry sets the assembly. An IP54 gland on an IP66 box leaves you an IP54 assembly, so match every gland and accessory to the box rating.
The dock-end box and its bonding
The dock-end junction box splits the feed to the posts, so give it the same 316L as the shore box, or GRP where it bolts against aluminum dock framing, which breaks the galvanic pair. The GRP vs stainless junction box comparison weighs that trade. Keep its bottom above both height limits, and put the terminals high inside, away from any water that gets past the lid.
Bond the box and the posts like any other metal part. NEC 250.4(A)(5) treats the equipment grounding conductor, not the earth, as the fault-current path. NEC Table 250.122 sizes that conductor from the rating of the overcurrent device ahead of it. The grounding and bonding guide covers the enclosure details, and the sub-panel bonding jumper size article works through the two sizing rules you apply where the feed splits.
Give every cable a strain relief at the box. Floats move with each wake and each tide, and a cable clamped to the dock frame feeds that motion straight into the terminations.
What to put on the order
| Line | Spec to send |
|---|---|
| Shore enclosure | Type 4X, 316L stainless wall-mount box, hinged gasketed door, removable mounting panel, wall-mount feet |
| Size | Any size in the stainless wall-mount line, from 6 x 4 x 4 in up to 60 x 36 x 16 in (H x W x D); larger sizes follow your drawing |
| Cutouts | One gland hole per portable cable run, positioned and sized to the gland's seal range and thread |
| Terminations | Terminal blocks or lugs marked for the cable's strand class (fine classes G, H, I, K, M) |
| Dock-end box | 316L stainless or GRP, bottom at least 12 in above deck and above the datum plane |
| Delivery | 10 business days from order; custom work from your approval of the drawing |
Send the gland count, the jacket outside diameter of your cable and the shore single-line with the drawing, and every cutout lands where the gland wants it. Stainless wall-mount enclosures cover the size range above, and orders go through the checkout of Industrial Monitor Direct, who builds, ships and supports every box.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 316L stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 316L stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 316L stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 6 × 6 × 4 in | 316L stainless | 6 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can the portable power cable land directly in the shore sub-panel?
Yes. NEC Article 555 sets no shore-side junction box: the cable lands on the panel's terminals or in its terminal gutter. The terminations must suit the cable's fine strand class, flexible classes G, H, I, K and M, not the Class B stranding a standard lug is evaluated with, and a multi-range gland must grip the jacket. Add a junction box only when the panel lacks suitable terminals or the feed splits to several floats.
How high does a junction box sit on a floating dock?
Above two limits at once. The electrical datum plane for a floating pier sits 30 in above the water level, and Article 555 wants dock components at least 12 in above the deck and never below the plane. On a deck 16 in above the water, the plane governs: 16 + 12 = 28 in falls short of 30 in, so mount the box bottom 15 in above the deck, one inch in hand.
Is a NEMA 3R panel enough on the shore at a marina?
Only in a covered, dry room. Type 3R is tested for rain, sleet and ice, not for the wave splash, wash-down and salt air a waterside wall takes. Out in the open, order Type 4X stainless: the Type 4X test adds 200 hours of salt spray, and 316L resists the chloride pitting that eats 304 and painted steel at the water.
What termination holds fine-stranded portable cable conductors?
A terminal marked for the cable's strand class, or a ferrule in front of a standard one. Standard breaker and block lugs are evaluated with Class B stranding, 7 strands on 8 to 2 AWG, while classes K and M run far finer. Crimp the ferrule with the matched tool, torque the screw to the value printed on the terminal, and check torque after the first season.
Which gland suits a portable power cable at the dock?
A multi-range gland picked by jacket outside diameter. As an example, a 3-conductor extra-hard cable with a 0.8 in [20 mm] jacket needs a gland whose seal range brackets 0.8 in; measure your jacket with calipers before ordering. Use a stainless or nickel-plated brass body in salt air, point the gland down or sideways, and leave a drip loop below the entry.
