Guide · Outdoor electrical
How to choose a weatherproof outlet box: gangs, hubs, metal vs. plastic
A weatherproof box looks simple, but the wrong hub count or gang size means a second trip to the supply house. Work through these five decisions and the box, cover and gasket will go together the first time.
1. How many devices? (gang)
One receptacle or switch needs a one-gang box. Two devices side by side — a GFCI and a timer, or two receptacles — need a two-gang box; pool equipment pads and shop exteriors often use three-gang. The cover must match the gang count exactly.
2. How many conduit entries, and what size? (hubs)
Boxes are described by the number of threaded hubs: a 3-hole box has one hub each side and one on the bottom; 4- and 5-hole boxes add entries on the back or top. Count the conduits that will actually enter the box, then pick the box with at least that many hubs — the spare ones are closed with the closure plugs supplied. Hubs are 1/2″ or 3/4″ NPT; match them to your conduit or liquid-tight connector. A 3/4″ hub can take a 1/2″ fitting with a reducing bushing, but not the other way around.
3. Metal or plastic?
Die-cast aluminum |
Polycarbonate |
|
|---|---|---|
Corrosion |
Powder-coated; good, but salt air and pool chemistry eventually mark it |
Immune to rust and pool chemicals |
Impact |
Best for abuse-prone locations |
Impact-resistant, UV-stabilised |
Grounding |
Box can be bonded and serve as part of the ground path with metal raceway |
Non-conductive; ground through the conductor |
Weight and cutting |
Heavier; drill for extra holes |
Light; easy to cut |
Typical use |
Commercial, industrial, rigid or IMC conduit |
Pools, coastal, landscape lighting, liquid-tight runs |
Both Sealproof plastic boxes and the die-cast boxes take the same covers.
4. Depth
Standard boxes suit receptacles, switches and most GFCIs. Deep GFCIs, timers and smart devices, or boxes with several conductors passing through, may need an extension ring. Extensions also rescue a box that ended up recessed behind new siding.
5. Cover and gasket
Wet-location receptacles need an extra-duty while-in-use cover; switches, blanks and damp-location receptacles take a flat cover. Always install the gasket, and replace it if it has hardened. Our guide In-use cover vs. weatherproof cover covers the code requirement in detail.
Round boxes
Round weatherproof boxes are for lampholders, floodlights and motion sensors, which mount on the 3-1/2″ round pattern. They are not interchangeable with rectangular device covers.
Mounting
Sealproof boxes have lugs for surface mounting to masonry, siding or a post. On a post, mount the box so the hubs face down or sideways, never up, and seal the top of any conduit stub. Where a box supports a fixture or a fan, use a box or brace listed for the load — see the fan brace.
A quick specification
“Weatherproof outlet box, one-gang, die-cast aluminum, powder-coated gray, three 1/2″ threaded hubs with closure plugs and gasket, cULus Listed for wet locations; with extra-duty while-in-use cover, clear, lockable. Sealproof or equal.”
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