Originally there was a flat prohibition on using flex for fixed wiring (apart from the final connection to fixed appliances) but that originated in the days when flex was much less substantial than premises wiring cables - typically being a couple of rubber singles with little more than a thin cotton braiding over. These days flexes have more robust PVC insulation and a PVC oversheath so apart from the conductor being stranded are pretty much identical and generally just as robust as rigid PVC/PVC cables.

   - Andy.

Good afternoon Andy,

Thanks for Feedback. You comments are quite clear.

I am looking for backup where Class 5 flexible cable is clearly mentioned suitable for fixed installations. We follow BS 7671:2018  here. If we compare Class 02 versus Class 05. Class 02 conductor is known to be suitable for wiring at fixed installations. But certain projects demands for class 05 flexible conductors. I want to ensure that class 05 usage in fixed installation is good by norms.

Satish Kumar said:

I want to ensure that class 05 usage in fixed installation is good by norms.

Well, flexible cables (Class 5 and Class 6 stranding) are actually specified for some installations, or parts of installations, within BS 7671.

Flexible cables must be acceptable (if properly selected, erected and protected for the installation conditions - as with all cables), because:

• Regulation 422.3.201 permits their use, although has some requirements for their construction or protection. This is supported by Regulation Group 521.9
• Regulation 413.3.4 has a particular requirement concerning their use in parts of the installation with protective measure double or reinforced insulation.
• Regulation 418.3.6 for electrical separation to more than one item of equipment requires flexible cables to incorporate a protective conductor
• They are required to be used for suspended current-using equipment (Regulation 522.7.2)
• They are required in installations in flexible structures, or where a structures are intended to be moved (Regulation 522.15.2,
• There are minimum cross-sectional areas for flexible cables "for any other purpose" in Table 52.3
• Some Part 7 special locations specify certain wiring systems, for which flexible cables are options, or mandated (Regulations Group 704.522.8, Regulation 717.411.3.1.2, Regulation Group 717.52, Regulation 721.521.2

Of course, when using stranded wires, appropriate terminals ought to be used, or, Class 5 or Class 6 conductors are to be terminated in terminals suitable only for Class 1 (solid) and/or Class 2 (stranded) they should be suitable prepared, for example with a ferrule. (See Regulation Group 526.9.)

I would add to Graham's comprehensive list that an adjustment is made for flexible cables in Table 4D2A, which very clearly applies to fixed installations, be they in conduit in walls, conduit on walls, etc.

Good morning Graham,

Really appreciated on above points shared. Indeed these were very helpful in getting quite clear on the different applications for class 05.

Though I noticed from your reply above that below regulations indeed can be used for installing the class 05 conductor ( Heavy duty Type having voltage rating of not less than 450/750V) for Fixed installation with Chris comments on adjustment is made for flexible cables in Table 4D2A.

• Regulation 422.3.201 permits their use, although has some requirements for their construction or protection. This is supported by Regulation Group 521.9
• when using stranded wires, appropriate terminals ought to be used, or, Class 5 or Class 6 conductors are to be terminated in terminals suitable only for Class 1 (solid) and/or Class 2 (stranded) they should be suitable prepared, for example with a ferrule. (See Regulation Group 526.9.)
• Since I don't have BS EN 50565-01 to understand real definition on described on Light, Ordinary, Heavy duty type. Grateful if you can help on same as well. This is part of regulation group 521.9 and 422.3.201.

Thanks & Regards,

Good morning Graham,

Really appreciated on above points shared. Indeed these were very helpful in getting quite clear on the different applications for class 05.

Though I noticed from your reply above that below regulations indeed can be used for installing the class 05 conductor ( Heavy duty Type having voltage rating of not less than 450/750V) for Fixed installation with Chris comments on adjustment is made for flexible cables in Table 4D2A.

• Regulation 422.3.201 permits their use, although has some requirements for their construction or protection. This is supported by Regulation Group 521.9
• when using stranded wires, appropriate terminals ought to be used, or, Class 5 or Class 6 conductors are to be terminated in terminals suitable only for Class 1 (solid) and/or Class 2 (stranded) they should be suitable prepared, for example with a ferrule. (See Regulation Group 526.9.)
• Since I don't have BS EN 50565-01 to understand real definition on described on Light, Ordinary, Heavy duty type. Grateful if you can help on same as well. This is part of regulation group 521.9 and 422.3.201.

Thanks & Regards,

Satish Kumar said:

when using stranded wires, appropriate terminals ought to be used, or, Class 5 or Class 6 conductors are to be terminated in terminals suitable only for Class 1 (solid) and/or Class 2 (stranded) they should be suitable prepared, for example with a ferrule. (See Regulation Group 526.9.)

This depends on terminal type.

to CENELEC standards:

• Terminals that have no marking can be assumed to be suitable for all classes of conductor, although you might want to use ferrules for class 5 and class 6 stranded conductors if they are to be regularly disconnected and reconnected, or where installation and maintenance activities would be slowed down drastically by having to re-strip to reconnect (for example industrial control panels, alarm systems, etc.)
• Terminals marked 'r' are suitable for rigid conductors (class 1 and class 2 only). Class 5 and Class 6 stranded conductors may be terminated if crimp ferrules can be used (although manufacturer's instructions should be followed for screwless terminals).
• Terminals marked 'sol' are suitable for class 1 (solid) conductors only. If manufacturers instructions permit, class 2, 5 and 6 conductors might be connected using crimp ferrules.
• Terminals marked 'f' may only be used for class 5 and class 6 stranded (flexible and extra-flexible respectively) conductors. Ferrules should not be used for Class 5 and Class 6 stranded conductors in terminals marked 'f'

Thanks Graham for above explanation.