Three Core Cables to BS 6622 / BS 7835

Application

The three core cables are designed for distribution of electrical power with nominal voltage Uo/U ranging from 3.6/6.6KV to 19/33KV and frequency 50Hz. They are suitable for installation mostly in power supply stations, indoors and in cable ducts, outdoors, underground and in water as well as for installation on cable trays for industries, switchboards and power stations.

Standards

BS 6622

BS 7835 (LSZH Version)

Construction

Conductor : Plain annealed copper or aluminium complying with IEC 60228/BS 6360. Copper conductors shall be stranded (class 2) and aluminium conductors shall be either solid or stranded (class 2).

Conductor Screen : Extruded layer of semi-conducting cross-linkable compound is applied over the conductor and shall cover the surface completely. The minimum thickness is 0.3mm and the maximum resistivity shall not exceed 500 Ohm-m at 90°C.

Insulation : Insulation is of cross-linked polyethylene compound XLPE (GP8) conforming to BS 7655-1.3 or EPR (GP7), conforming to BS 7655-1.2.

Table 1. Insulation Thickness

Nom. Cross Section Area	Insulation Thickness at Nominal Voltage
Nom. Cross Section Area	3.8/6.6KV (Um=7.2KV)	6.35/11KV (Um=12KV)	8.7/15KV(Um=17.5KV)	12.7/22KV(Um=24KV)	19/33KV(Um=36KV)
mm²	mm	mm	mm	mm	mm
70 – 185	2.5	3.4	4.5	5.5	8.0
240	2.6	3.4	4.5	5.5	8.0
300	2.8	3.4	4.5	5.5	8.0
400	3.0	3.4	4.5	5.5	8.0
Above 500	3.2	3.4	4.5	5.5	8.0

Insulaton Screen : Extruded layer of semi-conducting cross-linkable compound is applied over the insulation. The extruded semi-conducting layer shall consist of bonded or cold strippable semi-conducting compound capable of removal for jointing or terminating. As anoption, a semi-conducting tape may be applied over the extruded semi-conducting layer as a bedding for the metallic layer. The minimum thickness is 0.3 mm and the maximum resistivity is 500 Ohm-m at 90°C. The screen is tightly fitted to the insulation to exclude all air voids and can be easily hand stripped on site.

Inner Covering & Fillers : For cables with a collective metallic layer or cables with a metallic layer over each individual cores with additional collective metallic layers, semi-conducting inner covering and fillers shall be applied over the laid up cores. The inner covering is made of non hygroscopic material, except if the cable is to be made longitudinally watertight. The inner covering shall be extruded or lapped.

The approximate thickness of extruded inner coverings is given in Table 2 :

Table 2. Approximate Thickness of Extruded Inner Coverings

Ficititous Diameter over Laid Up Cores		Approx. Thickness of Extruded Inner Covering
mm		mm
>	<
-	25	1.0
25	35	1.2
35	45	1.4
45	60	1.6
60	80	1.8
80	-	2.0

*The approximate thickness of lapped inner coverings shall be 0.6mm.

Metallic Layer : The metallic layer shall be applied over each core or applied as a collective screen. The metallic screen shall consist of either copper tapes or a concentric layer of copper wires or a combination of tapes and wires. The metallic layer provides an earth fault current path, capable of withstanding fault current to earth of 1000A for one second at maximum temperature 160°C. Copper wires are applied over the conducting water blocking layer with a minimum diameter of 0.5mm. As an alternative, copper tape(s) with minimum thickness of 0.1mm can be applied with overlap. Total cross section of copper wire screen and copper tape screen layer are shown in Table 3a and 3b.

Table 3a. Total Cross Section and Max. DC Resistance of Copper Wire Screen

Nominal Cross-Section of Cables	Total Cross Section					Max. DC Resistance of Copper Wire Screen at 20℃
Nominal Cross-Section of Cables	3.8/6.6KV (Um=7.2KV)	6.35/11KV (Um=12KV)	8.7/15KV (Um=17.5KV)	12.7/22KV (Um=24KV)	19/33KV (Um=36KV)	Max. DC Resistance of Copper Wire Screen at 20℃
mm²	mm²					Ω
70	16	16	16	16	16	1.19
95	16	16	16	16	16	1.19
120	16	16	16	16	16	1.19
150	25	25	25	25	25	0.759
185	25	25	25	25	25	0.759
240	25	25	25	25	25	0.759
300	25	25	25	25	25	0.759
400	35	35	35	35	35	0.271
500	35	35	35	35	35	0.271
630	35	35	35	35	35	0.271

Table 3b. Total Cross Section and Max. DC Resistance of Copper Tape Screen (0.1mm)

Nominal Cross-Section of Cables	Total Cross Section & Max DC Resistance
	3.8/6.6KV (Um=7.2KV)		6.35/11KV (Um=12KV)		8.7/15KV (Um=17.5KV)		12.7/22KV (Um=24KV)		19/33KV (Um=36KV)
	Total Cross Section	Max. DC Resistance at 20℃	Total Cross Section	Max. DC Resistance at 20℃	Total Cross Section	Max. DC Resistance at 20℃	Total Cross Section	Max. DC Resistance at 20℃	Total Cross Section	Max. DC Resistance at 20℃
mm²	mm²	Ω	mm²	Ω	mm²	Ω	mm²	Ω	mm²	Ω
70	6.6	2.616	7.23	2.380	8.02	2.145	8.7	1.967	10.5	1.075
95	7.3	2.369	7.91	2.174	8.71	1.975	9.4	1.824	11.2	1.075
120	8.0	2.153	8.64	1.991	9.43	1.823	10.2	1.694	12.0	1.075
150	8.5	2.013	9.19	1.871	9.99	1.722	10.7	1.606	12.5	0.688
185	9.4	1.838	9.88	1.741	10.82	1.590	11.4	1.509	13.2	0.688
240	10.4	1.656	10.96	1.569	11.76	1.463	12.5	1.378	14.3	0.688
300	11.4	1.508	11.84	1.452	12.64	1.361	13.4	1.287	15.2	0.688
400	12.6	1.362	12.92	1.332	13.71	1.254	14.4	1.192	16.2	0.491
500	13.9	1.237	14.34	1.199	15.14	1.136	15.5	1.110	17.7	0.491
630	15.3	1.121	16.68	1.031	16.57	1.038	17.3	0.995	19.1	0.491

Separation Sheath (for armoured cable) : The separation sheath comprises a layer of extruded PVC, PE or LSZH. The nominal thickness is calculated by 0.02Du + 0.6mm where Du is the fictitious diameter under the sheath in mm. The nominal separation sheath thickness shall not be less than 1.2mm.

Armour (for armoured cable) : The armour consists of galvanized steel wire applied over the inner covering with diameter specified as in Table 4.