Flex
Flex is stranded electrical wire used for all plug-in mains appliance leads. It is also called flexible cable.
Cable on the other hand is unstranded mains wire not suited to repeated flexing, and is used for fixed installations.
Colour
Current colours:
- L - brown
- N - blue
- E - green/yellow striped
Old colours: (until about 1970)
- L - red
- N - black
- E - green
Colours on US appliance leads:
- black = live
- white = neutral
2 Core Flexes
Flexes are available with 2 or 3 cores (conductors). 2 core flex is only suitable for appliances that don't need an earth connection (marked 
), and should not be used for extension leads with 3 pin sockets.
2 core flexes are available in both round and oval shape. Oval (flat) uses less material, but any twisting of the flex is visible, whereas it isn't with round.
Multicore
Multicore mains flexes are also available for those uncommon tasks requiring more conductors. Non-mains multicores, such as alarm cable, are not suitable for mains use.
Insulation
PVC
Most flex has PVC insulation rated to 70°C.
90°C PVC is also available for use in hot locations, such as for immersion heaters. A higher temp rating also means a given conductor size may carry more current in some (very limited) circumstances. however practically it is not usually possible to take advantage of this increase in capacity since the normal BS 1363 plugs, sockets and flex connection units are not rated for the higher temperature.
Arctic
Arctic flex remains flexible at low temperatures, whereas regular PVC stiffens. Arctic flex is used for outoor appliances, eg on building sites. It is rated for use down to -40°C.
On sites yellow is used for 110v and blue for 240v.
Rubber
TRS (tough rubber sheath) is a flex with greater mechanical strength and damage resistance than PVC. It is used when some degree of rough use can be expected.
VIR is discussed further down.
Cloth
Flexes with a cloth outer have rubber inner insulation. These have a high temperature rated outer surface. They are well known for their use on irons.
Old cloth insulated flexes are prone to kinking, with the inner rubber insulated wires poking out at the kinks. New cloth insulated flexes have a layer of rubber under the cloth that discourages this from happening.
The rubber inner insulation can harden and break at the ends. This is often seen on old cloth flexes. When this occurs the flex can be cut back several inches to reveal healthy flex, and reconnected, if the rest of the flex is still healthy.
Whats it called
the very soft high temp plastic insulation sometimes found on irons.
Figure of 8
Figure of 8 shaped plastic flex was formerly used for low current mains uses. It has a single layer of insulation only, and live conductors are easily exposed by minor damage. It was used in several colours, including black, brown, white and clear.
Such flex has been unlawful to fit to mains appliances for decades, but is still occasionally seen in use. Today this flex type is used as speaker wire.
Twisted Pair
2 core cloth & rubber (VIR) twisted mains flex with no outer sheath was once in common use. Most was dark red or brown. This flex has been obsolete for decades, and is rarely seen today. Occasionally its seen on historic electrical goods, and when found is usually in a dangerous condition. Apart from not meeting modern safety requirements, the rubber tends to harden, perish and disintegrate over time, exposing bare live wires. Despite once being in widespread use, it is rarely seen today because it deteriorates badly over time.
Conductor Sizes
| Flex conductor size (mm²) | Approx max current (PVC insulation) |
|---|---|
| 0.5 | 3A |
| 0.75 | 6A |
| 1.0 | 10A |
| 1.5 | 15A |
| 2.5 | 20A |
| 4.0 | 32A |
Note that current carrying capacities are only approximate, and vary with exact construction and materials used for the flex.
For data on how much 90°C insulation changes current ratings, see Cable
Understanding Harmonised Cable Codes
An effort by CENELEC (a European standards committee) to harmonise the classification of flexible cables had lead to a coding system that you will often see used to specify the detailed characteristics of a bit of flex. These designations are often written in the form H05RN-F or H05BN-F etc.
The codes break down into three parts:
Part 1 of the Designation
Table 1a gives you the standards compliance and maximum nominal voltage
| Symbol | Conformance to Standards |
| H | Cable conforms with the harmonised standards |
| A | Cable conforms with a Recognised National Type, listed in a Supplement to the harmonised standards |
Table 1b Gives the voltage rating of the cable
| Symbol | Voltage Rating, Single/3Ph |
| 01 | >= 100/100V to < 300/300V |
| 03 | 300/300V |
| 05 | 300/500V |
| 07 | 450/750V |
Part 2 of the Designation
Table 2a gives you the insulating material and the designation of any non metallic sheath.
| Symbol | Material |
| B | Ethylene-propylene rubber (Continuous operation up to 90°C) |
| G | Ethylene-vinyl-acetate |
| J | Glass-fibre braid |
| M | Mineral |
| N | Polychloroprene (or equivalent material) |
| N2 | Special polychloroprene compound for covering of welding cables according to HD 22.6 |
| N4 | Chlorosulfonated polyethylene or chlorinated polyethylene |
| N8 | Special water resistant polychloroprene compound |
| Q | Polyurethane |
| Q4 | Polyamide |
| R | Ordinary ethylene propylene rubber or equivalent synthetic elastomer for a continuous operating temperature of 60ºC |
| S | Silicone rubber |
| T | Textile braid, impregnated or not, on assembled cores |
| T6 | Textile braid, impregnated or not, on individual cores of a multi-core cable |
| V | Ordinary PVC |
| V2 | PVC compound for a continuous operating temperature of 90ºC |
| V3 | PVC compound for cables installed at low temperature |
| V4 | Cross-linked PVC |
| V5 | Special oil resistant PVC compound |
| Z | Polyolefin-based cross-linked compound having low level of emission of corrosive gases and which is suitable for use in cables which, when burned, have low emission of smoke |
| Z1 | Polyolefin-based thermoplastic compound having low level of emission of corrosive gases and which is suitable for use in cables which, when burned, have low emission of smoke |
Table 2b gives a number of possible metallic coverings:
| Symbol | Sheath, concentric conductors and screens |
| C | Concentric copper conductor |
| C4 | Copper screen as braid over the assembled cores |
Table 2c for some special constructions of components of the cable:
| Symbol | Sheath, concentric conductors and screens |
| D | Strain-bearing element consisting of one or more textile components, placed at the centre of a round cable or distributed inside a flat cable |
| D5 | Central heart (non strain-bearing for lift cables only) |
| D9 | Strain-bearing element consisting of one or more metallic components, placed at the centre of a round cable or distributed inside a flat cable |
Next, you may get any of the following tacked onto the ends of codes from tables a to c above:
Table 2d Special constructions of whole cable
| Symbol | Special construction |
| No Symbol | Circular construction of cable |
| H | Flat construction of “divisible” cables and cores, either sheathed or non-sheathed |
| H2 | Flat construction of “non-divisible” cables and cores |
| H6 | Flat cable having three or more cores, according to DH 359 or EN 50214 |
| H7 | Cable having a double layer insulation applied by extrusion |
| H8 | Extensible lead |
Next an optional group for specifying the conductor material. This is only required for non copper conductors and will follow a dash.
Table 2e Conductor material
| Symbol | Conductor material |
| No Symbol | Copper |
| -A | Aluminium |
Lastly, Again these follow after a dash (the same one as that used to specify aluminium conductors above if present!)
Table 2f Conductor form
(note for cables with two forms of conductor, the specification applies to the phase conductor only)
| Symbol | Conductor form |
| -D | Flexible conductor for use in arc welding cables to HD 22Part 6 (flexibility different from Class 5 of HD 383) |
| -E | Highly flexible conductor for use in arc welding cables to HD22 Part 6 (flexibility different from Class 6 of HD 383) |
| -F | Flexible conductor of a flexible cable or cord (flexibility according to Class 5 of HD 383) |
| -H | Highly flexible conductor of a flexible cable or cord (flexibility according to Class 6 of HD 383) |
| -K | Flexible conductor of a cable for fixed installations (unless otherwise specified, flexibility according to Class 5 of HD 383) |
| -R | Rigid, round conductor, stranded |
| -U | Rigid round conductor, solid |
| -Y | Tinsel conductor (Tinsel conductors are used in flexes for small appliances were normal stranded flex would be likely to fatigue and break - its made with a conductive foil wrapped around a supporting textile or plastic core to provide the tensile strength) |
Part 3 of the Designation
Table 3 Number of cores and the nominal cross sectional area of each core.
| Symbol | Number and size of conductors |
| (number) | Number, n of cores |
| X | Times, where a green/yellow core is not included |
| G | Times, when a green/yellow core is included |
| (number) | Nominal cross-section, s, of conductor in mm²
(Note an N after the number of cores indicates the cores are identified by numbers rather than or in addition to colours) |
| Y | For a tinsel conductor where the cross-section is not specified |
Fitting all the bits together
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| Part 1 | Part 2 | Part 3 | ||||||||
| Related standard |
Rated voltage |
Insulating material |
Metallic coverings (2) |
Non-metallic sheath (2) |
Constructional components and special constructions |
Conductor material |
Conductor forms |
Number of cores | Times | Conductor size mm² |
| Symbols according to tables | ||||||||||
| 1a | 1b | 2a | 2b | 2a | 2c and 2d | 2e | 2f | 3 | ||
| H | 01 | B | C | B | D3 | No | -D | 1 | X | Y |
| D5 | symbol: | -E | 2 | 0.5 | ||||||
| A | 03 | G | C4 | G | copper | -F | 3 | G | ||
| ----- | -H | 4 | 0.75 | |||||||
| 05 | J | J | No symbol: | -A | -K | 5 | ||||
| circular | -R | etc | 1 | |||||||
| 07 | M | construction of | -U | |||||||
| cable | -Y | 1.5 | ||||||||
| N, N4 | N,N2,N4,N8 | |||||||||
| H | 2.5 | |||||||||
| Q, Q4 | H2 | |||||||||
| H6 | 4 | |||||||||
| R | R | H7 | ||||||||
| H8 | 6 | |||||||||
| S | S | |||||||||
| 10 | ||||||||||
| T, T6 | ||||||||||
| 16 | ||||||||||
| V, V2, | V, V2, V3, | |||||||||
| V3, V4 | V4, V5 | 25 | ||||||||
| Z, Z1 | Z, Z1 | etc | ||||||||
(1) If two or more symbols listed in the same column need to be used in a given designation, they shall follow each other in their radial sequence starting from the core axis or cable axis.
(2) The symbols might change their position in the designation with respect to the construction of the cable