I think it all depends on the detail of the conductor and terminal - but "suitably treated" could be as simple as twisting the strands together between thumb and first finger before inserting into the terminal, or twist and fold over if the conductor is small compared to the terminal, or ferrule.


   - Andy.

The best treatment is the use of the insulated coloured ferrules, which I even use in plugs, of the correct size for your wires. There are two colour codes for size, either may be used or even a mixture! Packs of 100 of most sizes are only about £1 so there is little reason not to use them. The entrance is tapered so they are easy to fit and crimp, although some thin fine wires may need to be twisted first. They go up in size to at least 10mm2, needing a bigger crimper, but the 2.5 mm2 down tool is about £10 and like a pair of pliers. Try here https://cpc.farnell.com/c/ferrules or RS etc

Many of the screw terminals in room thermostats and the like have a metal shield under the screw and are actually cage terminals.


Despite many of the English YouTube videos saying you need ferrules with both screw and cage terminals, the Germans quite definitely state you don’t need them in cage terminals.


I probably use more ferrules than the majority of domestic electricians, comments have been made by people I work with about this, my reply is I have been working too far away from home to have any callbacks.


Andy Betteridge

I too use ferrules where their use is sensible, in connector blocks for example.


Cage terminals don't warrant them.


One major use for me at least is dressing neutrals in RCBO boards. Shorten the existing tail to match the required position on the neutral bar, and re-ferrule.


Same with the flying FE lead if present.


In plugs I use the uncoded ferrules (with a slightly flared metal end, but no plastic 'funnel') because of space restrictions.

dressing neutrals in RCBO boards. Shorten the existing tail


When I've posted previously and questioned the use by some manufacturers of either 2 mm2 or 2,5 mm2 neutral tails on a 32 or 40 A RCBO in a board containing 70 deg C equipment and outgoing circuits, the topic bombed............


Regards


BAD

Well, a 2.5mm single with no over sleeve is clearly better cooled than one inside the jacket of T and E grouped with another one equally hot.

Look at car wiring for how far you can really push PVC singles without any issues - also I suspect a higher insulation temperature - the wylex ones seem to be silicone rubber, so are presumably OK at 150-200C in parts.

No dafter than the idea of 1.5mm cable for ring finals in pyrotenax cable (mind you I;ve not seen that mentioned for a while either) - only works because the cable tails get cooled where they fan out to be connected.

In any case, yes, I'm a ferrule person, but be sure they are the right size, and crunched with the right tools - a poorly fitted ferrule is worse than none at all, so do not use them if you do not have the tools.

I wish I could say "simples" but it's definitely NOT.


The answer to the OP is, it depends on either the product standard for the particular accessory or terminal, the manufacturer's instructions, or both.

There are 4 types of conductor in common use for power cables:

• Class 1 (solid) – with a single strand – usually used for some sheathed fixed wiring cables up to 2.5 mm².

• Class 2 (stranded) – a minimum of 7 strands – usually used for unsheathed fixed wiring cables, and some sheathed fixed wiring cables up to 2.5 mm², and all sheathed fixed wiring cables of 4 mm² and greater.

• Class 5 (flexible) – sometimes called finely stranded - flexible cables and internal appliance wiring. Also used in places where vibration is greater (e.g. main bonding in mobile and transportable units, and may be used in caravans and mobile and transportable units)

• Class 6 (extra flexible) – sometimes called extra-finely stranded - may be used in very high vibration environments or equipment.

Examples of where the standard specifies the types and sizes of cables that do not require special treatment include:

1. BS EN 61184 for lampholders requires the terminals for lampholders sold in the UK to be suitable for 0.5 mm² and 0.75 mm² flexible conductors for cordgrip lampholders, and 0.5 mm² to 1.0 mm² flexible conductors for threaded-entry lampholders. (in the EU, up top 2.5 mm2 flexible are permitted).
   
   Batten lampholders are only required to be suitable for 0.5 mm² to 2.5 mm² solid (class 1) conductors – so check with the manufacturer’s instructions before terminating stranded conductors in them without ferrules !

• BS 1363-2 requires portable socket-outlets with screw terminals to be suitable for connection of a single 1 mm² or 1.5 mm² flexible conductor. Therefore, if using 0.75 mm² flexible cable, at least a “doubling back” is required to obtain a suitable csa for the terminal.

• BS 1363-2 requires fixed socket-outlet line and neutral screw terminals to be suitable for connection of 1, 2 or 3 no. 2.5 mm² solid (class 1) or stranded (class 2) conductors, or 2 no. 4mm² conductors. Screw terminals for protective conductors shall be suitable for connection of 1, 2 or 3 no. 1.5 mm² or 2.5 mm² solid (class 1) or stranded (class 2) conductors, or 2 no. 4mm² conductors.

• BS 1363-4 requires incoming screw terminals to be suitable for the same size/no. of conductors as socket-outlets.
  
  Outgoing terminals (L, N and PE) must be suitable for connection of flexible (class 5) conductors in the range 0.5 mm² to 1.5 mm², or one conductor of solid (class 1) or stranded (class 2) with csa 1.5 mm² or 2.5 mm².

Examples of where manufacturer’s data or instructions are the only clue as to whether special preparation is required are:

1. Fixed socket-outlets to BS 1363-2 or connection units to BS 1363-4 with screwless terminals. The manufacturer may choose whether they are suitable for flexible (class 5) only, or solid + stranded (Class 1 + 2) only, or all 3 (class 1, 2 and 5).

• Some crimps – especially the common red, blue & yellow – may not be suitable for solid (class 1) or stranded (class 2) conductors. Usually, if suitable for solid or stranded conductors, the crimp will have ridges around the inside

• Some screwless connectors are only suitable for certain types of conductor – e.g. common screwless connectors without levers might only be suitable for solid or stranded (class 1 and 2) conductors.

I replaced a consumer unit, the guy who had installed the previous consumer unit had used insulated boot lace ferrules on the 25 mm meter tails inside the 35 mm cage terminals of the main switch.


I just pulled the ferrules off with my fingers and threw them away, they had not been crimped with a tool and even if they had I don’t think it would have made much difference. 


Now we can buy nineteen strand meter tails they will splay out more in the cage terminals and presumably fit better, so with either type of meter tail in a cage clamp it would appear that a ferrule would be detrimental.


However with fine strands under a screw some strands will be torn and severed, hence the benefit of the protection from the ferrule improves the termination.

My world was originally aircraft electrical wiring. The main thing to remember with crimps and ferrules is to match (as best you can) crimp tools to product/conductor type and manufacturer.

Easily done in aviation engineering because of the control standards in place, not so easy in general electrical installation.

A general rule in my view DO NOT use a not ratchet controlled crimper. That is a good starting place.

The term 'shear it and back a turn' springs to mind!


Colin

Great information,thanks Gents.

It's a shame that it isn't distilled by the IET Regs authors into, say, a table in 526 or the OSG.

Thanks again.