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Cable Capacities

Current-carrying capacities (Iz) for copper cables from BS 7671 Appendix 4 Tables 4D1A, 4D5, 4E4A and 4D4A.

Singles in Conduit (70°C Thermoplastic) — Table 4D1A

Singles in Conduit / Trunking — Table 4D1A, Iz (A)

Size (mm²)	Method A 1Φ (col 2)	Method A 3Φ (col 3)	Method B 1Φ (col 4)	Method B 3Φ (col 5)
1.0	11	10.5	13.5	12
1.5	14.5	13.5	17.5	15.5
2.5	20	18	24	21
4.0	26	24	32	28
6.0	34	31	41	36
10.0	46	42	57	50
16.0	61	56	76	68
25.0	80	73	101	89
35.0	99	89	125	110
50.0	119	108	151	134
70.0	151	136	192	171
95.0	182	164	232	207
120.0	210	188	269	239
150.0	240	216	300	262
185.0	273	245	341	296
240.0	321	286	400	346
300.0	367	328	458	394

Method A: enclosed in conduit in a thermally insulating wall. Method B: enclosed in conduit on a wall or in trunking.

1Φ: 2 cables, single-phase a.c. or d.c. 3Φ: 3 or 4 cables, three-phase a.c. Ambient 30 °C, conductor 70 °C.

BS 7671: Table 4D1A Open Calculator →

Flat Twin & Earth (70°C Thermoplastic) — Table 4D5

Flat Twin & Earth — Table 4D5, Iz (A)

Size (mm²)	Method A (col 6)	Method B (col 7)	Method C clipped direct (col 8)
1.0	11.5	13	16
1.5	14.5	16.5	20
2.5	20	23	27
4.0	26	30	37
6.0	32	38	47
10.0	44	52	64
16.0	57	69	85

Flat T&E is a single-phase cable: Table 4D5 has no three-phase column, and it is tabulated to 16 mm² only. Ambient 30 °C, conductor 70 °C.

Method A: in conduit in a thermally insulated wall. Method B: in conduit on a wall or in trunking. Installation Methods 100–103 (in insulated ceilings and stud walls) are separate columns of Table 4D5.

BS 7671: Table 4D5 Open Calculator →

SWA Multicore (90°C Thermosetting) — Table 4E4A

Armoured Multicore, 90°C — Table 4E4A, Iz (A)

Size (mm²)	Method C 1Φ (col 2)	Method C 3Φ (col 3)	Method E 1Φ (col 4)	Method D1 1Φ (col 6)
1.5	27	23	29	25
2.5	36	31	39	33
4.0	49	42	52	43
6.0	62	53	66	53
10.0	85	73	90	71
16.0	110	94	115	91
25.0	146	124	152	116
35.0	180	154	188	139
50.0	219	187	228	164
70.0	279	238	291	203
95.0	338	289	354	239
120.0	392	335	410	271
150.0	451	386	472	306
185.0	515	441	539	343
240.0	607	520	636	395
300.0	698	599	732	446

90 °C ratings. Reg 512.1.5: use them only where the equipment manufacturer confirms the terminals are suitable for the conductor operating temperature; otherwise use Table 4D4A (70 °C), below.

1Φ: one two-core cable. 3Φ: one three- or four-core cable. Method E: free air or perforated tray. Method D1: in ducts in the ground, 20 °C ground, 2.5 K·m/W, 0.7 m deep; other methods 30 °C ambient.

BS 7671: Table 4E4A

SWA Multicore at 70°C Terminals — Table 4D4A

Armoured Multicore, 70°C — Table 4D4A, Iz (A)

Size (mm²)	Method C 1Φ (col 2)	Method C 3Φ (col 3)	Method E 1Φ (col 4)	Method D1 1Φ (col 6)
1.5	21	18	22	22
2.5	28	25	31	29
4.0	38	33	41	37
6.0	49	42	53	46
10.0	67	58	72	60
16.0	89	77	97	78
25.0	118	102	128	99
35.0	145	125	157	119
50.0	175	151	190	140
70.0	222	192	241	173
95.0	269	231	291	204
120.0	310	267	336	231
150.0	356	306	386	261
185.0	405	348	439	292
240.0	476	409	516	336
300.0	547	469	592	379

Use for 90 °C thermosetting SWA where the equipment terminals are rated for 70 °C conductors only (Reg 512.1.5 NOTE 3) — most MCBs, RCBOs and accessories unless the manufacturer states otherwise.

Method D1: in ducts in the ground, 20 °C ground, 2.5 K·m/W, 0.7 m deep; other methods 30 °C ambient.

BS 7671: Table 4D4A Open Calculator →

Zs Values

Correction Factors

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