BARE CONDUCTOR

Copper Stranded Conductor BS 7884

Copper Stranded Conductor to BS 7884 is a bare overhead conductor built from concentric layers of hard-drawn wires, supplied either in high-conductivity copper or in copper-cadmium alloy C108. It is meant for overhead power lines and for the overhead lines of electric traction systems. The TDS lists 20 copper constructions from 7/1.35 to 37/2.50 (10 to 185 mm²) and 21 copper alloy constructions from 3/2.30 to 19/4.00 (12 to 240 mm²).

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BS 7884 deals with round conductors, solid or stranded, made of hard-drawn high-conductivity copper or of copper alloy for overhead power transmission and overhead electric traction. It sets the material, the dimensions, the mechanical and electrical properties and the stranding of these conductors (BS 7884 Clause 1). This page covers the stranded types: a straight centre wire surrounded by one or more helical layers of wires of equal diameter, each layer running in the opposite direction to the layer below (BS 7884 Clause 3.2).

Conductor Construction

Copper wires: High-conductivity copper with the composition of BS 6926 grade C100, C101 or C102, the grade being chosen by the producer (BS 7884 Clause 4.1)
Copper alloy wires: Copper-cadmium alloy C108 with the composition of BS 2873; the masses given for the copper alloy conductors are valid for this alloy only (BS 7884 Clause 4.1 and Table 4)
Wire size and mass: Before stranding, every wire stays within the diameter limits of Table 1 (copper) or Table 2 (copper alloy), is round to within 2% of its nominal diameter and has a mass per length at most 2% over the nominal value (BS 7884 Clause 4.2.2)
Construction: Number and diameter of wires as listed in Tables 3 and 4, with a conductor mass per length at most 2% over the nominal value (BS 7884 Clause 4.2.3)
Lay: Lay ratios within the limits of Table 5; adjacent layers are laid in opposite directions, the outer layer right-hand unless the purchaser asks for left-hand, and the wires sit evenly and tightly on the layer beneath (BS 7884 Clause 4.5.1)
Joints: Wires are drawn without joins other than those made in the rod before drawing; in stranding, cold pressure welds are allowed, and for conductors of more than seven wires brazed or resistance-welded joins as well, with at least 15 m between any two joins in the finished conductor (BS 7884 Clause 4.5.2)
Identification: If the purchaser asks, one wire of the outer layer is tinned to mark the material (BS 7884 Clause 4.5.3)
Surface: Wires clean and smooth, with no defects that would harm their use (BS 7884 Clause 4.5.4)

Lay Ratios

Wires in Conductor	Layer of 3 Wires	Layer of 6 Wires	Layer of 12 Wires	Layer of 18 Wires
3	11 to 16	–	–	–
7	–	13 to 17	–	–
19	–	13 to 17	12 to 15	–
37	–	13 to 17	12 to 15	10.5 to 13

The lay ratio is the length of one full turn of a wire divided by the outside diameter of the layer it belongs to (BS 7884 Clause 3.7 and Table 5).

Values Used in the Tables

Property	Hard-Drawn Copper	Copper Alloy C108
Resistivity at 20 °C	0.01777 µΩ·m	0.02155 µΩ·m
Conductivity	97% IACS	80% IACS
Density used for the masses	8890 kg/m³	8945 kg/m³

These figures come from BS 7884 Clause 4.4 and the notes to Tables 3 and 4. In the TDS, the nominal resistance follows from the nominal wire diameter and the average lay ratio, while the maximum resistance follows from the smallest permitted wire diameter and the shortest lay ratio. The minimum breaking load of each conductor is the total of the minimum breaking loads of its wires times 0.92 for 3-wire and 7-wire conductors, or times 0.90 for 19-wire and 37-wire conductors. Overall diameters are approximate.

Typical Applications

Overhead power transmission lines
Overhead lines of electric traction systems
Existing overhead lines whose fittings suit these British conductor sizes

Copper Stranded Conductor to BS 7884 is stranded from hard-drawn copper or copper-cadmium alloy wires for overhead lines. The table below sums up the requirements of the standard; the properties of each construction are listed in the TDS tab.

Technical Characteristics

Applicable Standard	BS 7884
Standard Scope	Solid and stranded round conductors of hard-drawn copper and copper alloy for overhead power transmission and overhead electric traction
Conductor Materials	Hard-drawn high-conductivity copper (BS 6926 grade C100, C101 or C102) or hard-drawn copper-cadmium alloy C108 (BS 2873)
Copper Constructions	3, 7, 19 and 37 wires; 20 sizes, 10 to 185 mm²
Copper Alloy Constructions	3, 7, 19 and 37 wires; 21 sizes, 12 to 240 mm²
Overall Diameter	Approx. 4.05 to 17.75 mm (copper); 4.95 to 20.00 mm (copper alloy)
Resistivity at 20 °C	0.01777 µΩ·m, 97% IACS (copper); 0.02155 µΩ·m, 80% IACS (copper alloy)
Minimum Breaking Load	3752 N to 68860 N (copper); 6968 N to 117900 N (copper alloy)
Mass Tolerance	Wire and conductor mass per length no more than 2% over nominal
Wire Roundness	Within 2% of the nominal wire diameter
Lay Ratio	11 to 16 for 3-wire conductors; 13 to 17, 12 to 15 and 10.5 to 13 for the 6-, 12- and 18-wire layers
Lay Direction	Opposite in adjacent layers; outer layer right-hand unless left-hand is ordered
Joints	Cold pressure welds; brazed or resistance-welded joins also allowed above seven wires; at least 15 m apart
Wrap Test	No breakage for copper wires under 5.6 mm and copper alloy wires under 3.5 mm
Identification	One tinned wire in the outer layer, on request

Ordering Information

Please state the quantity; the standard, BS 7884; the conductor material, copper or copper alloy; the construction as number of wires and wire diameter, for example 19/2.50; whether the outer layer is to be left-hand; whether you wish to witness tests on the stranded conductor; delivery needs such as coil size or spool type; whether a declaration of conformity or a report of inspection results is needed, and which tests; any special surface condition such as greased wires; any special marking, labelling or packing; and any required mass or length per coil or spool.

Hard-Drawn Copper Stranded Conductors

Nominal Area of Cross-Section	Stranding and Wire Diameter	Approx. Overall Diameter	Nominal Mass	Resistance at 20 °C		Minimum Breaking Load
Nominal Area of Cross-Section	Stranding and Wire Diameter	Approx. Overall Diameter	Nominal Mass	Nominal	Max.	Minimum Breaking Load
mm²	No./mm	mm	kg/km	Ω/km	Ω/km	N
10	7/1.35	4.05	89.82	1.788	1.829	3752
14	7/1.60	4.80	126.2	1.273	1.303	5267
16	3/2.65	5.70	148.3	1.082	1.106	6194
16	7/1.70	5.10	142.4	1.128	1.154	5946
25	7/2.10	6.30	217.3	0.7391	0.7563	9073
32	3/3.75	8.06	296.9	0.5405	0.5520	12400
32	7/2.46	7.38	298.2	0.5386	0.5497	12442
35	7/2.50	7.50	308.0	0.5215	0.5337	12860
50	7/3.00	9.00	443.5	0.3622	0.3706	18520
50	19/1.80	9.00	435.8	0.3727	0.3819	17700
70	7/3.55	10.65	621.1	0.2586	0.2646	25930
70	19/2.10	10.50	593.2	0.2738	0.2806	24090
95	19/2.50	12.50	840.7	0.1932	0.1980	34140
100	7/4.30	12.90	911.2	0.1763	0.1810	36540
120	19/2.80	14.00	1055	0.1540	0.1578	42830
125	19/2.90	14.50	1131	0.1436	0.1471	45940
150	19/3.20	16.00	1377	0.1180	0.1208	55940
150	37/2.25	15.75	1334	0.1233	0.1264	53880
185	19/3.55	17.75	1695	0.09582	0.09815	68860
185	37/2.50	17.50	1647	0.09981	0.1024	66490

Hard-Drawn Copper Alloy (Copper-Cadmium C108) Stranded Conductors

Nominal Area of Cross-Section	Stranding and Wire Diameter	Approx. Overall Diameter	Nominal Mass	Resistance at 20 °C		Minimum Breaking Load
Nominal Area of Cross-Section	Stranding and Wire Diameter	Approx. Overall Diameter	Nominal Mass	Nominal	Max.	Minimum Breaking Load
mm²	No./mm	mm	kg/km	Ω/km	Ω/km	N
12	3/2.30	4.95	112.4	1.743	1.780	6968
16	7/1.70	5.10	143.3	1.368	1.399	8883
22	7/2.00	6.00	198.3	0.9882	1.011	12290
25	7/2.10	6.30	218.7	0.8959	0.9171	13550
30	7/2.30	6.90	262.3	0.7469	0.7645	16260
35	7/2.50	7.50	309.9	0.6324	0.6471	19210
38	7/2.60	7.80	335.2	0.5847	0.5983	20780
45	7/2.90	8.70	417.0	0.4698	0.4809	24600
55	7/3.20	9.60	507.8	0.3859	0.3950	29950
70	19/2.10	10.50	596.8	0.3316	0.3403	35990
75	7/3.70	11.10	678.8	0.2887	0.2954	38010
95	19/2.50	12.50	845.9	0.2343	0.2400	51010
100	7/4.30	12.90	916.9	0.2138	0.2195	51160
120	19/2.80	14.00	1061	0.1862	0.1914	60890
125	19/2.90	14.50	1138	0.1739	0.1784	65310
150	19/3.20	16.00	1386	0.1428	0.1465	79530
150	37/2.25	15.75	1342	0.1493	0.1533	80490
180	19/3.50	17.50	1658	0.1196	0.1225	95140
180	37/2.50	17.50	1657	0.1209	0.1242	99330
200	19/3.70	18.50	1853	0.1068	0.1696	100900
240	19/4.00	20.00	2165	0.09153	0.09378	117900

Wire Tests

In accordance with BS 7884 Clause 6.1, samples are cut before stranding from at least 10% of the wire lengths that go into a consignment, one sample from each chosen length, each large enough for all the tests.
In accordance with BS 7884 Clauses 4.2.2 and 4.5.4, each wire is checked for diameter against Table 1 or Table 2, for roundness within 2% of the nominal diameter and for a mass per length no more than 2% over nominal, and its surface is clean, smooth and without harmful defects.
In accordance with BS 7884 Clause 4.3.1, the breaking load of each wire is tested to BS EN 10002-1 and is not below the value of Table 1 or Table 2.

Conductor Tests

In accordance with BS 7884 Clause 6.2, samples of finished conductor are taken from at least 10% of the drums in a consignment.
In accordance with BS 7884 Clause 4.2.3, the number and diameter of wires agree with Table 3 or Table 4, and the conductor mass per length is no more than 2% over nominal.
In accordance with BS 7884 Clause 4.3.1, the breaking load of the conductor is found either by a tensile test on the whole conductor to BS EN 10002-1 or by adding the breaking loads of its wires tested before stranding and multiplying by 0.92 for 3 and 7 wires or 0.90 for 19 and 37 wires; the result is not below the minimum in the TDS.
In accordance with BS 7884 Clause 4.3.1, where wires are taken out of the finished conductor for testing, each reaches at least 92.5% and their average at least 94% of the breaking load in Table 1 or Table 2.
In accordance with BS 7884 Clause 4.3.2 and Annex C, wires taken from the conductor sample, copper wires under 5.6 mm and copper alloy wires under 3.5 mm in nominal diameter, are wound in eight tight turns round a mandrel of their own diameter, six turns are unwound and wound back the same way, and the wire shows no sign of fracture when looked at by eye.
In accordance with BS 7884 Clause 4.4 and Annex D, the resistance per length is measured directly by the routine method of BS 5714, with its reference method used in case of dispute, corrected to 20 °C with the factors of Table D.1 (copper) or Table D.2 (copper-cadmium), and does not exceed the maximum in the TDS.
In accordance with BS 7884 Clauses 4.5.1 and 4.5.2, the lay ratios are within Table 5, adjacent layers run in opposite directions with the outer layer as ordered, and joins in the finished conductor are at least 15 m apart.

Retests, Documents and Packing

In accordance with BS 7884 Clause 6.3, a sample that fails a test is tested twice more; if the failures then outnumber the passes, that reel, parcel or drum is rejected, and if 10% of the samples chosen from a consignment fail, the whole consignment is regarded as not conforming.
In accordance with BS 7884 Clause 7, when the purchaser asks and the supplier agrees, a declaration of conformity to BS EN 1655 or a report of inspection results is issued for the goods.
In accordance with BS 7884 Clause 8, marking, labelling and packing follow the purchaser’s requirements where these are agreed, and are otherwise left to the supplier.

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