Solid vs stranded conductors: choosing the right cable

A cable feeding a fixed distribution board, a wire inside a control panel and a lead travelling with a machine axis have different jobs. All three may use stranded conductors. That does not make them interchangeable.

Solid wire uses one metal strand per conductor. Stranded wire uses several. Fine-stranded construction makes a conductor easier to bend, but a cable still needs the right electrical rating, insulation, termination and mechanical design for its application. Flexibility is one part of the specification.

Start with what the cable will do

For building-wire terminology, see the guide to NYA, NYM, TTR and antigron cables. Those designations describe more than whether the copper is solid or stranded. Environmental suitability is another separate decision, covered in cables for outdoor and underground installation.

“Single-core” does not mean “solid”

Core count and strand construction answer different questions. A single-core cable contains one core; that core can have a solid or stranded conductor. A multicore cable contains several cores, and each has its own conductor construction.

For example, a specification reading 1 × 6 mm², Class 2 copper describes a single-core cable with a stranded conductor. There is no contradiction. Likewise, a three-core cable may contain three flexible conductors; it does not become “many-core” because each conductor contains numerous copper strands.

Core identification describes the circuit function. It should not be confused with conductor construction. The guides to L, N and PE markings and live, neutral and earth colours explain that distinction.

Read the conductor class before calling a cable flexible

IEC 60228 distinguishes Class 1 solid, Class 2 stranded, Class 5 flexible and Class 6 more flexible conductors. Class 2 is stranded construction intended for fixed installation; it should not be confused with the fine-stranded wire commonly used where flexibility is required.

A higher class number is not an overall quality score. Nor does Class 5 or Class 6, by itself, establish a cable's suitability for a moving carrier. Repeated bending loads the complete cable structure, including insulation, core arrangement, screening and sheath.

For a moving axis, look for declared operating conditions: permitted bend radius, motion type and the manufacturer's relevant test or service-life data. A cable that handles bending may have different limits for twisting. “Easy to bend by hand” is not a motion specification.

More strands do not automatically mean more current

Strand count is not an ampacity multiplier. A cable's allowable current depends on its construction and installation conditions, including temperature, grouping and the number of loaded conductors. The starting point is current-carrying capacity for the relevant cable size, with the applicable conditions and correction factors.

Keep the ratings separate. Amperes measure current; the cable's voltage rating concerns its intended electrical service and insulation. If those terms are unfamiliar, the explanation of voltage provides the other half of the picture. Neither rating can be established by squeezing the cable or counting visible strands.

Material matters too. Replacing copper with aluminium involves different electrical and termination requirements, even when the printed cross-sectional areas match. See copper versus aluminium conductors before treating them as equivalents.

Compare resistance and size, not outside diameter

A thick jacket can make a cable look substantial without increasing its conductor area. A stranded bundle also contains spaces between wires. Its outside diameter is therefore not a direct measurement of the metal cross-section.

Nominal cross-sectional area is a standardised designation. Relevant construction and resistance requirements apply; a simple diameter measurement is not a complete compliance check. Different conductor classes at the same nominal size can also have different maximum resistance limits. Use the actual cable data when resistance affects the design.

This becomes useful on longer runs. According to Ohm's law, current flowing through resistance produces a voltage drop. The practical consequences are explained in voltage drop in long cables.

Where a specification uses AWG, consult the AWG-to-mm² conversion guide. Converting the unit still leaves installation and protection to be checked. The broader procedure is covered in selecting cable cross-sectional area, with familiar sizes discussed in the guide to 1.5, 2.5, 4 and 6 mm² cables.

The terminal must accept the conductor you have chosen

Check the terminal's permitted conductor types, size range and preparation instructions. Some terminals accept bare fine-stranded wire; others have different requirements. A stated range for solid conductors should not automatically be applied to flexible conductors or ferruled ends.

WAGO's 221 range is one example of connectors accepting solid, stranded and fine-stranded conductors within model-specific limits. That capability should not be assumed for every spring connector. The comparison of WAGO connectors, screw terminals and taped joints explains why the connection method deserves its own selection step.

Ferrules are not universally mandatory. Follow the equipment manufacturer's requirements. Where ferrules are used, their dimensions and the crimping tool must suit the connection. A ferrule neither increases the wire's current rating nor turns an unsuitable cable into a suitable one. See wire ferrules, cable lugs and crimping tools for the differences.

Do not remove strands to make an oversized conductor fit. Solder-tinning a flexible end is also not a substitute for an approved screw-terminal preparation: solder can deform under pressure and heat, reducing the security of the connection.

Questions that come up when replacing a cable

Can flexible cable replace rigid cable of the same size?
Sometimes an approved flexible cable is suitable for fixed wiring, but matching the size alone is insufficient. The cable type, installation rules, voltage and temperature ratings, terminals and mechanical support must all suit the job.

Does an extension lead's flexibility tell me its wattage limit?
No. The complete lead includes plugs, sockets and cable, and its declared limit applies to that assembly under stated conditions. Use the guide to how many watts an extension lead can handle when assessing connected loads.

Does the same distinction apply to network cable?
Yes, copper network conductors can also be solid or stranded, but power-cable sizing is not enough to select a network connection. Cable category, connector compatibility and transmission requirements matter. The guide to Ethernet cable types covers that separate application.

Can I identify an old wire by its colour?
Colour is useful information, not proof of the actual connection. Refer to old and new wiring colours, and have the circuit identified correctly. Protective-conductor continuity is a separate requirement explained in the grounding guide.

Before ordering: specify the required core count, conductor material, nominal area, conductor class, service conditions and compatible termination. For moving applications, include the actual motion duty. Installation work should be carried out by a competent person with the supply isolated and absence of voltage verified.

Technical references: Eland Cables — single-core cable with a stranded conductor; ABB — conductor classes and connections; Nexans — conductor resistance and nominal cross-section; LAPP — current rating and installation conditions; igus — continuous-flex cable construction; WAGO — 221 conductor compatibility; Phoenix Contact — ferrules and conductor preparation.