Junction boxes and wire connectors: IP ratings, outdoor boxes and what goes inside

A junction box does one job: it keeps a cable joint safe, dry and out of reach. The wrong box – an indoor one in a garden, a gland that does not fit the cable – is how a joint fails. This guide sorts the range by where the joint will be, explains the IP ratings on the labels, and covers the connectors that actually make the joint inside the box.

First: where is the joint?

The IP rating is the short answer. The first digit is dust, the second is water, and the second digit is the one that matters for choosing a box.

• IP44 – protected from splashes. Indoors, or a covered outdoor spot.
• IP55 / IP65 – protected from water jets. Outdoor walls, sheds, garages.
• IP66 – powerful jets. Exposed outdoor positions.
• IP68 – continuous immersion. Ground level, ponds, anything that will sit in water.

Indoors

For a tidy joint inside a ceiling void, under a floor or behind a unit, the IP44 mini junction box is the compact choice: 3-core, rated 16 A / 250 V, about 50 x 32 x 20 mm, with the terminal block, cover and a 7 mm protection coil in the box. It also comes in a pack of 5 with rubber plugs.

Outdoors on a wall

Two options depending on the cable. The IP65 outdoor junction box comes in 2-way and 3-way versions with screw-fixed glands for cable of 5 to 10.5 mm diameter, works from –35 to 120 °C, and is sold singly or in packs of 3, 5 or 10. For a larger enclosure – several joints, or a small controller to house – the ABS junction boxes run from a 50 mm round box to 300 x 250 x 120 mm. Note the rating changes with size: the two smallest are IP55, 150 x 110 x 70 mm and up are IP65.

If you need a weatherproof home for a socket or switch rather than a bare joint, the IP66 outdoor electric box is an empty 1-gang or 2-gang enclosure with a clear hinged, lockable cover. It is supplied empty – the socket or switch is separate.

Wet ground, ponds and buried runs

For a joint that will sit in water or soil, only IP68 will do. The range has four shapes:

• IP68 3-way junction box – the general outdoor joint, about 120 x 60 mm with glands, in packs of 1, 2 or 10.
• IP68 T connector – for taking a branch off a run; cable 6 to 12 mm, wire 0.3 to 4 mm².
• IP68 inline I and Y connectors – for joining two cable ends in a straight line (I) or splitting one into two (Y), slimmer than a box.
• IP68 underground junction box – rated 24 A / 450 V, 0.5 to 2.5 mm² conductors, cable 3 to 12 mm depending on the gland seal, made for burial.

Cable glands: the seal is only as good as the fit

A gland grips the cable where it enters the box and is what makes the IP rating real. It has to match the cable diameter – too loose and water tracks in along the sheath. The IP68 nylon glands come in M16 and M20 (black) and PG13.5 and PG19 (white), with a nitrile rubber seal, singly or in packs of 5 or 10. Check the thread size of the box’s knockout before ordering.

What goes inside: the connectors

The box keeps the water out; the connector makes the joint. Four types, from quickest to most traditional:

• Lever connectors – lift the lever, push the wire in, close it. Reusable, no screwdriver. The compact lever connectors are 32 A / 250 V in 2, 3 and 5 way, strip 9–10 mm, in packs from 1 to 100. The 40 A lever splitters take 0.5 to 6 mm² wire and have a screw-mounting ear so they fix inside a box.
• Push-in connectors – for solid or stranded wire of 0.75 to 2.5 mm², 20 A / 400 V, in 2, 4 and 6 way. The push-in connectors are the smallest and cheapest, and are single-use once a wire is in.
• Choc block – the 12-way screw terminal strip you cut to length. The 12 way connector strip comes in 5 A, 6 A, 10 A, 15 A and 60 A ratings, heat resistant to 65 °C. Pick the rating above the circuit’s load.

Whichever you use, the connector’s current rating must be at least that of the circuit, and the wire size must sit inside the connector’s stated range.

Safety

Installation should be carried out by a competent person with the power switched off. A box rated for the location, a gland that fits the cable and a connector rated for the current are the three things that make a joint safe.

What to buy

• Indoors: IP44 mini junction box, 16 A
• Outdoor wall: IP65 2/3-way box with glands or ABS enclosures 50–300 mm
• Wet or buried: IP68 3-way box, T connector, underground box
• Inside the box: lever connectors, push-in connectors, choc block
• Browse all connectors and junction boxes, and the LED driver guide if the joint feeds low-voltage lighting

Frequently asked questions

Is IP65 enough for a garden? On a wall or post, yes. At ground level, in a border or anywhere water collects, use IP68.

Can I bury an IP68 box? The underground box is made for it. The other IP68 boxes are for wet and submerged positions above ground.

Lever or push-in? Lever if you may ever need to undo it; push-in for a permanent joint where space is tight.

Which gland size do I need? Match the box’s knockout thread (M16, M20, PG13.5 or PG19) and check the cable diameter sits in the gland’s range.