BS 6899:1991 pdf free download.Specification for Rubber insulation and sheath of electric cables.
1 Scope
BS 6899 specifies the physical and electrical requirements for the types of rubber insulation and sheath of electric cables given in table 1. The relevant test methods for verification of compliance are given either in BS 6469 or in the appendices of this standard. XLPE compound (designated as type GP8) has been included.
NOTE. The titles of the publications referred to in this standard are listed on the Inside back (‘OVPF.
2 Defmitions
For the UFOSCS of this British Standard the following definitions apply, together with those given in BS 1755, RS :3558 and HS 4727.
2.1 median value
When several test results have been obtained and ordered in an increasing or decreasing succession, the median value is the middle value if the number of available values is cxid, and is the mean of the two middle values if the number is even.
2.2 variation
The difference between the median value after ageing and the median value without ageing, expressed as a percentage of the latter.
3 60 °C insulation
3.1 60 °C Insulation, type El 1
The insulation shall consist of a vulcanized rubber compound in which the characteristic constituent is a natural or synthetic rubber, or a mixture of the two, formulated and vulcanized so as to comply with the performance requirements of this standard.
3.2 ‘Ist requirements for physical and electrical properties
3.2.1 Tensile properties before and after ageing
3.2.1.1 General
When tested as described in the methods given in appendix A the properties of the insulation shall comply with 3.2.1.2 and 3.2.1.3 and, as appropriate, 3.2.1.4 and 3.2.1.5.
3.2. 1.2 7l’nsile properties qf u naqed flWtFria! The tensile strength and elongation at break shall be not less than the values given in table 2.
3.2. 1.3 Tnsik’ j;rojx’rties qfter 10 days in air at
70±1°C
3.2.1.3.1 The tensile strength and elongation at break shall be not less than the values given in table 2.
3.2.1.3.2 If the median value of the tensile strength after this ageing test is equal to or greater than 5.0 N/mm2 (ej in figure 1), the median values of the tensile strength and elongation at break shall not differ from the median values obtained without ageing by more than 40 % of the median values without ageing, and in addition the material shall comply with 3.2.1.4.

6 85 °C sheath3.2.1.3.3 If the median value of the tensile strength after this ageing test is lower than 5.0 N/mm2, hut not less than 4.2 N/mm2 (e. in figure 1), the material shall in a(hlition comply with 3.2.1.5.
3.2. 1.4 71’n.cile proJN’rt us ((tier 4 days in oxygen at 71) ± 1 O(
3.2.1.4.1 The tensile strength and elongation at break shall he not less than the values given in table 2.
3.2.1.4.2 If the median value of the tensile strength after this ageing test is equal to or higher than 5.0 N mm2 and if the change in tensile strength or elongation at break after the ageing test in air (3.2.1.3) does not exceed 25 % (f1 in figure 1), the median value after ageing in the oxygen 1)0mb shall not differ from that obtained without ageing by more than:
(a) 40 % of the median value without ageing, in the case of tensile strength, and
(b) 30 % of the median value without ageing, in the case of elongation at break.
3.2. 1.4.3 If the median value of the tensile strength after this ageing test is equal to or greater than 5.0 Nrmm2 and if the change in tensile strength or elongation at break after the ageing test in air (3.2.1.3) exceeds 25 % (f2 in figure 1), the median value after ageing in the oxygen bomb shall not (liffer from that obtained without ageing by more than:
(a) 25 % of the median value without ageing, in the case of tensile strength, and
(b) :15 % of the median value wit ho ageing, Ill the case of elongation at break.
3.2.1.4.4 If the median value of the tensile strength after the ageing test in the oxygen bomb for 4 (lays is less than 5.0 N mm2, but not less than
4.2 Nrmm2 (f3 in figure 1), the niaterial shall in addition comply with 32.1.5.
3.2. 1.5 fl’nsik’ piwil h’s (!frr 7 days in o.qgen at
70 ± I °C
The tensile strength and elongation at break shall be not less than the values given in table 2. The maximum variation shall be a.s given in table 2.
3.2.2 Retests of tensile properties before ageing If the tensile tests carried out in accordance with 3.2. 1 were not conducted at an ambient temperature of 20 ± 5 O(’ and any maximum variation specified in 3.2. 1 between tensile properties before and after ageing is exceeded, a single retest shall be carried out using the procedure described in A. 2( a) at exactly t he same temperature as that at which the tensile test after ageing Was carrie(l out.
6.1 Types of sheath
The sheath shall be one of the following types:
(a) ordinary duty oil-resisting and flame retardant type RS3; or
(b) heavy duty oil-resisting and flame retardant, type RS4.
For each type, the sheath shall consist of a compound based on a synthetic rubber, formulated and vulcanized so as to comply with the performance requirements of this standard. The colour of the compounds shall be black unless otherWise specified in the British Standard for the particular cable.
NUI’E 1. Sheaths of the types gwen in 6.1 do not normally sUpport combustton, but this prnperty is affected by other components of the cable and hence requirements for flame retardance, when relevant. are given in British Standants for finished cables.
NOTE 2. A cable employing sheath complying with the ageing in oil test requirement in 6.2 Is not necessarily suitable for continuous Use in oil.
6.2 1st requirements for physical and electrical properties
When tested as described in the methods given in appendix B the properties of the sheath shall be in accordance with the requirements gven En table 5 for the particular type of material.
7 90 °C insulation and sheath
7.1 Types of compound
7.1.1 Ordinary duty, type GP4, GP5. GP6 and GP7
The insulation shall be based on ethylene propylene rubber which when vulcanized complies with the performance requirements of this standard.
7.1.2 Ordinary duty, type GP8
The insulation shall be a therinoset material formed by the crt ss-linking of I hernu plastic polyethylene compound either by chemical or by irradiation methods, So as to comply with the performance requirements of this standard.
7.1.3 Ordinary duty, type RS5
The sheath shall be based on ethylene propylene rubber which when vulcanized complies with the performance requirements of this standard.
N( TFK. The colour of the material should be ey.
7.2 ‘Thst requirements for physical and electrical properties
When tested as described in the methods given in appendix B the properties of the insulation or sheath shall he in accordance with the requirements given in table (i for the particular type of material.
8 110 °C insulation or sheath
8.1110 °C insulation or sheath, type El 3
The insulation or sheath shall consist of a vulcanized compound in which the characteristic constituent is ethylene vinyl acetate or equivalent, formulated so as to comply with the iwrformance requirements of this standard.
8.2 Test requirements for physical and electrical properties
When tested as described in the methods given in appendix 11 the propertieS of the insulation or sheath shall be in accordance with the requirements given in table 7.
9 150 °C insulation or sheath
9.1 150 °C insulation or sheath, type El 2 The insulatkrn or sheath shall consist of a vulcanized compound in which the characteristic constituent is a silicone rubber, formulated so as to comply with the performance requirements of this standard.
9.2 Test requirements for physical and electrical properties
When tested as described in the methods given in appendix ii the properties of the insulation or sheath shall be in accordance with the requirements given in table 8.