Low-Voltage Cable Sizing per IEC 60364-5-52 — Current-Carrying Capacity and Voltage Drop
Design reference compiled by cBallast. 5-page PDF; the full content is on this page.
Compiled by
cBallast
Subject
Low-voltage installation cable
Document type
Design reference
Reference
IEC 60364-5-52 : 2019
Issued
2026-07-14
Pages
5
Format
Web page and PDF
Low-voltage cable sizing procedure per IEC 60364-5-52. Covers current-carrying capacity (Iz) tables for common installation methods (buried, on tray, in conduit, in wall), correction factors for grouping and ambient temperature, voltage drop calculation, and short-circuit thermal withstand. Includes reference tables for PVC and XLPE insulated copper cables from 1.5 to 240 mm².
The three sizing constraints
A low-voltage cable is sized on three simultaneous constraints: current-carrying capacity Iz ≥ design current Ib (with protection device In in between); voltage drop ΔU ≤ the design limit (3% for lighting, 5% for motor + power circuits per BS 7671 / IEC 60364); and short-circuit thermal withstand — the cable must survive the maximum prospective fault current for the time the protective device takes to clear it (I²t ≤ k²S²).
Installation-method reference letters
Method
Description
A1
Insulated single cores in conduit in thermally insulating wall
A2
Multi-core cable in conduit in thermally insulating wall
B1
Insulated single cores in conduit on wall
B2
Multi-core cable in conduit on wall
C
Cables clipped direct to wall or in ceiling void
D1
Multi-core cable in conduit or duct buried in ground
D2
Multi-core cable buried direct in ground
E
Multi-core cable in free air (on tray, spaced from wall)
F
Single-core cables touching in free air
G
Single-core cables spaced in free air
Current-carrying capacity — PVC-insulated copper (Iz in A, 70 °C, 30 °C ambient)
Size (mm²)
A1
B1
C
D1
E
1.5
13.5
16.5
19.5
22
22
2.5
18
23
27
29
31
4
24
30
36
37
41
6
31
38
46
46
53
10
42
52
63
60
72
16
56
69
85
78
97
25
73
90
112
99
128
35
89
111
138
119
157
50
108
133
168
140
190
70
136
168
213
173
240
95
164
201
258
204
290
120
188
232
299
231
335
150
216
-
344
261
386
185
245
-
392
293
441
240
286
-
461
339
520
Correction factors
Ambient temperature (°C)
PVC factor
XLPE factor
10
1.22
1.15
20
1.12
1.08
30 (reference)
1.00
1.00
40
0.87
0.91
50
0.71
0.82
60
0.50
0.71
Number of grouped circuits (touching, on tray)
Grouping factor
1
1.00
2
0.80
3
0.70
4
0.65
5
0.60
6
0.57
9
0.52
12
0.45
Voltage drop
Approximate voltage drop for a copper cable carrying its rated current: ΔU (V/A·km) values are tabulated by cable size and configuration. Multiply by design current Ib in A and cable length in km to get the total drop. IEC 60364 recommends the total drop from origin to the load's terminals should not exceed 3% for lighting or 5% for other circuits (including motor start).
Size (mm²)
2-core 1-phase (V/A·km)
3-core 3-phase (V/A·km)
1.5
29.0
25.0
2.5
18.0
15.0
4
11.0
9.5
6
7.3
6.4
10
4.4
3.8
16
2.8
2.4
25
1.75
1.50
35
1.25
1.10
50
0.93
0.80
70
0.63
0.55
95
0.46
0.40
120
0.36
0.31
Short-circuit thermal withstand
Cable insulation limits the temperature the conductor can reach during a short-circuit before insulation damage. The permitted let-through I²t = k² × S², where S is conductor cross-section in mm² and k depends on insulation and conductor material.
In reference method B2 (multi-core cable in conduit on a wall) the table gives 18–31 A depending on installation detail and conductor count; open methods rate higher. The installation method row, not the cable alone, decides the figure.
Why does the same cable have several ratings?
IEC 60364-5-52 rates by installation method (A1–E): a conductor buried in insulation sheds heat worse than one clipped in free air, so the identical cable may differ by 30–40 % between methods.
What derating factors apply on ships and in plants?
Grouping with other circuits, ambient above 30 °C and thermal insulation each multiply the base rating down; the guide's correction tables stack multiplicatively.
Is 1.5 mm² enough for a 16 A circuit?
Only in favourable methods — its B2 ratings start at 13.5 A. Verify the method and corrections before using 1.5 mm² at 16 A protection.