The free diy home improvement guide with answers to your questions on a wide range of do it yourself projects.


Junction Box

Junction boxes may be used to connect cables subject to the current regulations. All electrical connections must have durable electrical continuity, adequate mechanical strength and protection.

Screw terminal junction box

Where junction boxes with screw terminals are used, these must be accessible for maintenance, testing, and inspection.

Maintenance free junction box

Where the junction box will not be accessible, a maintenance free junction box must be used.

So, for example, a junction box fixed to a joist under a floor will clearly not be accessible and will need to be of the maintenance free type. Whereas, a junction box mounted on the wall of an airing cupboard will be fully accessible, and a screw terminal type box can be used.

If you are unsure whether the box would be deemed accessible, the simplest answer is to fit a maintenance free type.

Screw terminal junction box

Mounting a screw terminal junction box

1. Mount the junction box by screwing to a suitable surface. You may need to fit a wooden batten to support it on.

Rotating cover to suit required number of outlets

2. Most junction boxes have covers which can be rotated to allow the required number of access points to suit the number of cables being connected.

Cables stripped and prepared

3. The cables to be connected at the screw terminal junction box should be stripped and prepared in the normal way. See our Cable Stripping Guide for detailed information on this. Check the required length of exposed conductor to suit the connection terminal. Also ensure that when stripping the outer sheath of the cable you only strip what is required. Unsheathed sections of the cable must be fully enclosed inside the box.

Fitting the conductors into the junction box terminal connection

4. Slacken the terminal screws in the junction box. Fit the exposed section of the conductors beneath the screw ensuring that no bare conductor is left exposed. Tighten the screw to secure the conductors.

Checking connections and fitting the junction box cover

5. Once all connections have been made in this way, double check your connections then fit the cover.

If you look at a standard screw terminal type junction box you will see that there are several potential problems.

  • There is no facility for clamping the cable within the junction box. This means that any strain on the cable may pull on the connection terminals causing them to loosen.
  • The limited space inside the box may lead to unsheathed cable not being fully enclosed within the junction box.
  • Where flex is connected, it can be difficult to ensure that all strands of the conductor are fully and securely housed within the terminal connection.

Maintenance free junction box

1. Maintenance free junction boxes overcome these problems and may be used where the box will not be readily accessible.

Maintenance free junction box components

2. The Wagobox type shown in the pictures here are very neat and easy to use. Both push type, and cage clamp type, terminals are available to suit a range of different ampages and number of poles

Push type and cage clamp type connectors

3. Both the push type and cage clamp type terminals can be used for solid conductors. Flex has multiple fine strands so only the cage clamp type is suitable for this.

Stripped cables ready for connection

4. Strip and prepare the ends of the cables to be connected and select appropriate terminal connectors. Check the required length of exposed conductor to suit the connection terminal. Also ensure that when stripping the outer sheath of the cable you only strip what is required. Where the cable is held in the cable clamp this section must be fully sheathed.

5. Connect the conductors to the terminals as required.

Securing conductor in push type connector

6. For push type, the conductor is simply pushed fully home into the connector ensuring that none of the bare conductor is left exposed. The conductor can be released by rotating and pulling.

Securing conductor in cage clamp type connector

7. For cage clamp type, the clamp is lifted to open the cage and the conductor inserted fully into the connector ensuring that none of the bare conductor is left exposed. The clamp is then closed to secure the conductor. The conductor can be released by lifting the clamp and pulling.

Inserting connectors into junction box

8. The terminal connectors are then inserted into the retaining slots at the end of the junction box.

Securing sheathed cable in cable clamp

9. The cables are slotted into the cable clamps at the other end of the box to hold them securely and prevent any strain on the connectors.

Snapping the junction box lid closed

10. The lid of the box is snapped back on and the box can be clipped onto the small mounting bracket.

An additional advantage with this type of maintenance free junction box over the screw terminal type is that all connections can be made outside of the box first. This gives you more working space making the job far easier to complete.


Electics Safety warning

box alertThis material is for information purposes only. Strict rules govern what electrical work can be done without notification and inspection.
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