Joining wiring within trunking - crimp or solder?

[TommyH]

Hi there

Please scroll down for crimp/solder question!

I have an application where I need to add a surface-mount box onto a piece of 100mm trunking. There are already other surface mount boxes on this same piece of trunking, and I've got all the parts, except that wherever there's a hold cut in the trunking, and a surface box attached, there's a little bit of 20mm externally threaded tubing run through the hole with nuts on both sides, I assume to protect the cable from the edging.

Does anyone know what the term for this is, and where I could get some? Screwfix don't seem to have anything, the closest they have is PVC female conduit connectors which I could cut down.

Thanks, Tom

 

[Zambezi]

We used to call the brass externally threaded bits bushes (not sure what they call them in this country?)
Normally it would be brass bush through the hole in the trunking into a coupling then another brass bush through the socket outlet back-box into the same coupling.

It seems they are called bushes here too
http://www.tlc-direct.co.uk/Images/Products/size_3/CO20MBB.JPG

 

[TommyH]

That's perfect - thanks! I got 100 M20 'Brass bushes' with back nuts off ebay for £12 all in. Unfortunately they're the long ones so they'll stick into the trunking a bit but beggars can't be choosers. I have a 20mm punch as well so no easy to cut holes too.

Thanks very much

 

[TommyH]

I've got a second question now - the point of this is that I want to split out and parallel a number of sockets within the 100mm trunking - to have a second copy of each socket. (The reason for this unusal setup is because they're dimmed lighting sockets).

This means I'm going to need to join two wires within the trunking - what is going to be the best way of doing this? I don't think there's enough slack to be able to join them in the back of the socket, once it's on the surface box, so I'll either have to solder them or crimp them to make a Y-split.

They are going to be two wires of about 1.5mm square each - The existing one may be single core.

What's going to be the safest way to do this? I reckon I'll either need yellow crimps and a decent tool (hehe) or I can solder and heat-shrink them.

Or will they fit in blue crimps? That should go up to about 2mm square, so I'm not sure.

There's also terminal block, but this trunking can't really be inspected inside and it's not very nice. I would want to put terminal block inside a choc box, and then this is going to eat up space in the trunking.

Thanks again guys

 

[ElectricDunc]

Those through crimps are only designed for one conductor in each end. Reds are for 1-1.5mm, blue for 2.5mm and yellow for 4-6mm. If your extending multiple wires then block connectors or 3 pole push connectors would be a better bet. Is this a theatre install?

 

[electronicsuk]

I've got a second question now - the point of this is that I want to split out and parallel a number of sockets within the 100mm trunking - to have a second copy of each socket. (The reason for this unusal setup is because they're dimmed lighting sockets).

This means I'm going to need to join two wires within the trunking - what is going to be the best way of doing this? I don't think there's enough slack to be able to join them in the back of the socket, once it's on the surface box, so I'll either have to solder them or crimp them to make a Y-split.

I don't understand this at all. Why can you not put two wires into each terminal on the existing socket, thus allowing you to put a second one in parallel? From your description this is almost certainly some form of radial, so there shouldn't be any problems in doing this. How can there 'not be enough slack' for this connection method unless you were planning on moving the existing outlets?

 

[Spark123]

2 x 1.5 =

Don't put more than one conductor into a crimp anyway - it is horrible. Why can't you just do the connections in the boxes - won't there be plenty of room using conduit singles?
Soldering and heat sleeving is acceptable.

 

[ElectricDunc]

What sort of sockets are on this trunking? 13A, 15A round pin, 5A round pin or 16A commando? What are you planning on plugging in to these sockets? Are we talking Par 56, Fresnels or something completely different?

 

[Spark123]

Oh no - not another theatre sparky

 

[TommyH]

Those through crimps are only designed for one conductor in each end. Reds are for 1-1.5mm, blue for 2.5mm and yellow for 4-6mm. If your extending multiple wires then block connectors or 3 pole push connectors would be a better bet. Is this a theatre install?

It's adding sockets onto a dimmer lighting system, yeah - basically we have sockets attached to triac dimmers, but the sockets are positioned in ridiculous places (adjoining rooms, etc), but the trunking carrying the cable runs right past where we need them.

A three-pole push connector looks like a good solution, but I could also just solder them - space inside the trunking is a premium. Is there anything wrong with soldering?

 

[TommyH]

I don't understand this at all. Why can you not put two wires into each terminal on the existing socket, thus allowing you to put a second one in parallel? From your description this is almost certainly some form of radial, so there shouldn't be any problems in doing this. How can there 'not be enough slack' for this connection method unless you were planning on moving the existing outlets?

Because the existing sockets are further along the trunking, I was looking to split out of the cable on the way to the original socket. Not all of them are accessible either - some of them run from the trunking into plaster etc.

 

[Spark123]

Is it wired in conduit singles? Can you pull back the cable and replace the length of cable between the two sockets?

 

[TommyH]

Is it wired in conduit singles? Can you pull back the cable and replace the length of cable between the two sockets?

It is, but I don't think it would pull back - some of these lengths run 20m from the original sockets through all kinds of twists and corners. I don't think it would be possible to access the trunking to replace it either.

 

[TommyH]

What sort of sockets are on this trunking? 13A, 15A round pin, 5A round pin or 16A commando? What are you planning on plugging in to these sockets? Are we talking Par 56, Fresnels or something completely different?

Standard MK surface mount boxes, there's a mixture of 13A switched and 15A unswitched on the trunking depending on application. (Either ring mains or sockets for the dimmed lighting system). Nothing is drawing a very large load, the dimmers are only 2000W anyway so despite being 15A connectors they can't draw more than 8A. Most are small fixtures with only around 300W a channel, it's mostly 50W GU10 fixtures.

 

[RF Lighting]

Have you thought about getting an electrician in to do the work?