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.
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
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.
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.
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.
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.