In the UK it seems pretty common to see junction boxes with built-in screw terminals that are used only for splicing wires from 2 or more cables together.

Typical example:

enter image description here


Sample wiring diagram:

enter image description here


[These particular links are just examples.]

Are these acceptable for use in the US? (assuming "typical" building codes which I know vary locally).

Given that the jbox is installed in an accessible location and used as per its specifications as to volts/amps, I'm not sure what other factors might determine if these could / could not be used?

Although standard US jboxes are versatile, an advantage of these UK style boxes is that they are quite compact and they assist in making what seem to be very secure connections. Also the round cover is cleverly designed to leave open only as many side 'ports' as there are cables entering; so no holes have to be punched nor covered. Its basically an all-in-one type product for the common splicing situations.

So I've always been surprised that (essentially) the same thing doesn't seem to be available here. They seem DIY-friendly in particular.

(That said, when I lived in the UK I recall many of these were cheap brittle plastic and had to be installed carefully to avoid breakage.)

  • It's worth noting that these are usually referred to as 'Lighting' junction boxes in the UK; they have a fourth terminal for the switched-live, and are generally only rated for a relatively low current (10A or so). – SiHa Dec 1 '19 at 20:02

I'm pretty darn sure the answer is "no"

Non-metallic boxes, as well as oddly shaped/sized metal boxes, in the US are required to be permanently marked (labeled) with their "official" volume in cubic inches so that the correct box fill calculations can be run for them. This is Codified in NEC 314.16(A)(2):

(2) Other Boxes. Boxes 1650 cm³ (100 in.³) or less, other than those described in Table 314.16(A), and nonmetallic boxes shall be durably and legibly marked by the manufacturer with their volume(s). Boxes described in Table 314.16(A) that have a volume larger than is designated in the table shall be permitted to have their volume marked as required by this section.

I seriously doubt that IEC-style splicing boxes would carry such a volume marking, rendering them unusable in the US then and there. Furthermore, the size of that box is similar to a North American pancake box, which lacks the volume needed for tapping even a 14AWG NM cable, by Code. (At most, you can splice two 14/2 cables together in a pancake box, or use that style of box in its normal habitat, namely hosting a dead-end light fixture.)

As a result of this, I seriously doubt these are at all usable in the US, and that's before you get to the fact that the one you've linked is likely cheap Cheese-pipeline garbage that's not even suitable for use in a UK installation.


In addition to what ThreePhase noted, there's another potential problem. In this type of box you have to attach all your wires to the same terminal in some styles. Some of these boxes are bus types, meaning the terminals on a block are connected. Take your wiring diagram. Are the neutrals and grounds tied together on a single block? If so, that's not only not allowed by code anywhere, it's unsafe.

  • 2
    The ones I had seen in the UK were definitely not "bus" type; each screw was electrically independent. – StayOnTarget Sep 5 '20 at 22:25

It is interesting that I would not think the method of sticking a bunch of wires into a plastic and metal "knob" and turning them would be safe!

I have used the above type of boxes for years in attic spaces but only found out a couple of years ago that:

"This is further reinforced in Appendix 15 of the Wiring Regulations which states “Junction boxes with screw terminals must be accessible for inspection, testing & maintenance or, alternatively, use maintenance-free terminals / connection (Regulation 526.3)”.

I am told screw terminal should be tested for tightness at some interval but nobody does it.

The boxes above easily get over filled as you do not have as much room as the diagram above shows and it can be a problem getting two or three wires under one screw. The copper conductor can also get damaged. The terminals are not connected @Machavity.

I have now gone over to the Wago type of terminal block system which is maintenance free and more customisable. It has spring type clamps which makes everything easier and has different types of terminal blocks, number of connections etc. I doubt these are these used in the USA?

enter image description here

  • 3
    The Wago type connectors are sometimes used in the US, but not in a special junction box made to accept them. They are just used in standard US jboxes often in place of wire nuts. – StayOnTarget Dec 2 '19 at 0:36
  • Yeah -- the special Wago j-boxes suffer from the same problem as the round ones in the OP do, namely that they're nonmetallic but not volume-marked to my understanding... – ThreePhaseEel Dec 2 '19 at 0:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.