Electrical Conductor Sizing and Common Cable Types

A practical guide to conductor cross-sections, indicative current ratings and cable designations, with tables based on ČSN 33 2000-5-52.

When designing and installing electrical wiring, it is important to choose the right conductor or cable type and size. This choice affects the safety, service life and performance of the installation. Below you will find key values and conductor designations based on applicable standards.

The values below are for guidance and are based on ČSN 33 2000-5-52, which provides current-carrying capacities for electrical wiring according to the wiring type and installation method.

Permissible currents for copper conductors (cables) with PVC insulation

The permissible current depends on the conductor cross-section, insulation type and installation method. The table below gives indicative permissible currents for PVC-insulated copper conductors by installation method.

The table applies at a conductor temperature of 70°C, ambient air temperature of 30°C and ground temperature of 20°C. Values are indicative only.

Permissible currents for copper conductors (cables) with PVC insulation
Conductor cross-section [mm²]	Copper core diameter [mm]	In an insulated wall, in conduit or directly [A]	In conduit on a wall [A]	Cable directly on a wall, ceiling or floor [A]	Cable directly buried in the ground [A]
1	1.12	10.5	12	13.5	23
1.5	1.4	13	15.5	17.5	28
2.5	1.8	18	21	24	38
4	2.24	24	28	32	48
6	2.8	31	36	41	61
10	3.55	42	50	57	81
16	4.5	56	68	76	105
25	5.6	73	89	96	134
35	6.7	89	111	119	161
50	8	108	134	144	191
70	9.5	136	171	184	236
95	11	164	207	223	280
120	12.4	188	239	259	317
150	13.8	216		294	359
185	15.4	248		341	401
240	17.5	286		403	464
300	19.6	329		464	525

Indicative rated currents for selected conductor and cable types

Conductors must be sized not only according to their rated current, but also according to cable length (voltage drop), short-circuit parameters and cooling conditions.

Values are indicative only.

Indicative rated currents for selected conductor and cable types
Conductor cross-section [mm²]	Copper core diameter [mm]	H05V-U (CY) [A] single-core	H05VV-F (CYSY) [A] 3-core	H05RR-F (CGSG) [A] 3-core	H05RN-F (CGTGU) [A] 3-core
0.75	0.97	16	14.5	10.5
1	1.12	19	17	12.5
1.5	1.4	25	21	16	15.5
2.5	1.8	33	29	21	21
4	2.24	45	39	29	28
6	2.8	58		37	36
10	3.55	81		50	49
16	4.5	109		69	67
25	5.6	146			87
35	6.7	181			109
50	8	219			142
70	9.5	281			170
95	11	341			205

ČSN/CENELEC designation conversion table

ČSN/CENELEC designation conversion table
ČSN / former designation	CENELEC / harmonised designation	Use / note
CY	H05V-U / H07V-U	Single-core solid conductor for conduit
CYA	H05V-K / H07V-K	Single-core stranded conductor for trunking and enclosures
CYKY	NYM	Fixed power cable for indoor and some outdoor installations
CYLY	H03VV-F / H05VV-F	Flexible PVC cord with stranded cores for appliances
CYKYLo	NYIF / NYM-O,J (flat)	Fixed flat cable with solid cores for installation under plaster
CYSY	H05VV-F	Flexible cable for equipment and appliances
CGSG	H05RR-F	Light-duty rubber cable for portable appliances
CGTG	H07RN-F	Rubber cable for demanding conditions and outdoor use
O	H03VV-F	Light-duty flexible cable (2 cores), for example for luminaires
OY	H05VV-F	Light-duty PVC appliance cable (3–5 cores)
OZ	H05VV5-F	Screened cable for control systems and equipment
SYKFY	J-YY	Fixed communication cable for low-voltage signals
J-Y(St)Y	J-Y(St)Y	Screened communication cable, for example for security systems

CENELEC harmonised cable designations follow a defined structure. Each position conveys specific information.

Designation structure

Designation structure
Position	Meaning	Examples / options
1	Standard type	H = harmonised according to an HD standard
2–3	Rated voltage	03 = 300/300 V, 05 = 300/500 V, 07 = 450/750 V, 1 = 600/1000 V
4	Insulation type	V = PVC, R = rubber, G = thermoplastic, Z = halogen-free
5	Sheath or additional insulation type	V = PVC, R = rubber, N = neoprene, Z = halogen-free
6	Conductor construction	U = solid, K = stranded, F = flexible multicore

Designation examples:

H05VV-F = harmonised, 300/500 V, PVC insulation, PVC sheath, flexible stranded conductor
H07RN-F = harmonised, 450/750 V, rubber insulation, neoprene sheath, flexible conductor
H05V-K = harmonised, 300/500 V, PVC insulation, no outer sheath, stranded conductor

Recommendations

Always follow the current version of ČSN 33 2000-5-52, Low-voltage electrical installations – Part 5-52: Selection and erection of electrical equipment – Wiring systems.
For longer cable runs, take voltage drop into account.
For outdoor and underground installation, consider the cooling conditions.

This article provides indicative information. Final sizing should always be based on the project documentation and applicable technical standards.