2.9.1 Properties of insulating materials
The choice and application of insulating materials shall take into account the needs for electrical, thermal and mechanical strength, frequency of the WORKING VOLTAGE and the
working environment (temperature, pressure, humidity and pollution).
Natural rubber, hygroscopic materials and materials containing asbestos shall not be used as insulation.
Driving belts and couplings shall not be relied upon to ensure electrical insulation, unless the belt or coupling is of a special design that removes the risk of inappropriate replacement. Compliance is checked by inspection and, where necessary, by evaluation of the data for the material.
Where necessary, if the data does not confirm that the material is non-hygroscopic, the hygroscopic nature of the material is determined by subjecting the component or subassembly employing the insulation in question to the humidity treatment of 2.9.2. The insulation is then subjected to the relevant electric strength test of 5.2.2 while still in the humidity cabinet, or in the room in which the samples were brought to the prescribed temperature.
2.9.2 Humidity conditioning
Where required by 2.9.1, 2.10.8.3, 2.10.10 or 2.10.11, humidity conditioning is conducted for 48 h in a cabinet or room containing air with a relative humidity of 91 % to 95 %. The temperature of the air, at all places where samples can be located, is maintained within 1 °C of any convenient value t between 20 °C and 30 °C such that condensation does not occur. During this conditioning the component or subassembly is not energized.
With the concurrence of the manufacturer, it is permitted to increase the 48 h time duration. Before the humidity conditioning the sample is brought to a temperature between t and t + 4 °C.
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2.9.3 Grade of insulation
Insulation shall be considered to be FUNCTIONAL INSULATION, BASIC INSULATION, SUPPLEMENTARY INSULATION, REINFORCEDINSULATION or DOUBLE INSULATION.
The application of insulation in many common situations is described in Table 2H and illustrated in Figure 2H, but other situations and solutions are possible. These examples are informative; in some cases the necessary grade of insulation may be higher or lower. Where a different grade may be necessary, or if a particular configuration of energized parts is not represented in the examples, the necessary grade of insulation should be determined by considering the effect of a single fault (see 1.4.14). This should leave the requirements for protection against electric shock intact.
In certain cases, insulation may be bridged by a conductive path (for example, where 1.5.6, 1.5.7, 2.2.4, 2.3.4 or 2.4.3 applies) provided that the level of safety is maintained.
For
INSULATION elements. Where DOUBLE INSULATION is used, ELV CIRCUITS or unearthed conductive
parts are permitted between the BASIC INSULATION and the SUPPLEMENTARY INSULATION
provided that the overall level of insulation is maintained.
A BOUNDING SURFACE is treated as an unearthed SELV CIRCUIT if it is part of either:
− an unearthed conductive ENCLOSURE; or − a non-conductive ENCLOSURE.
Compliance is checked by inspection.
IEC 60950-1 : 2005 IS 13252 (Part 1) : 2010
DOUBLE INSULATION it is permitted to interchange the BASIC INSULATION and SUPPLEMENTARY
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Table 2H – Examples of application of insulation
Location of insulation Grade of
insulation between and Figure 2H Key to
FUNCTIONALa unearthed SELV CIRCUIT
or double-insulated conductive part
– earthed conductive part
– double-insulated conductive part – unearthed SELV CIRCUIT
– earthed SELV CIRCUIT
– earthed TNV-1 CIRCUIT F1 F2 F2 F1 F10 f
earthed SELV CIRCUIT – earthed SELV CIRCUIT
– earthed conductive part – unearthed TNV-1 CIRCUIT – earthed TNV-1 CIRCUIT F11 F11 F12 f F13 f ELV CIRCUIT or basic-
insulated conductive part
– earthed conductive part – earthed SELV CIRCUIT
– basic-insulated conductive part – ELV CIRCUIT F3 F3 F4 F4 earthed HAZARDOUS VOLTAGE SECONDARY CIRCUIT
earthed HAZARDOUS VOLTAGE
SECONDARY CIRCUIT F5 TNV-1 CIRCUIT TNV-1 CIRCUIT F7 TNV-2 CIRCUIT TNV-2 CIRCUIT F8 TNV-3 CIRCUIT TNV-3 CIRCUIT F9 series-parallel sections of a transformer winding F6
BASIC PRIMARY CIRCUIT – earthed or unearthed HAZARDOUS VOLTAGE SECONDARY CIRCUIT
– earthed conductive part – earthed SELV CIRCUIT
– basic-insulated conductive part – ELV CIRCUIT B1 B2 B2 B3 B3 earthed or unearthed HAZARDOUS VOLTAGE SECONDARY CIRCUIT
– unearthed HAZARDOUS VOLTAGE SECONDARY CIRCUIT
– earthed conductive part – earthed SELV CIRCUIT
– basic-insulated conductive part – ELV CIRCUIT B4 B5 B5 B6 B6
unearthed SELV CIRCUIT
or double-insulated conductive part – unearthed TNV-1 CIRCUIT – TNV-2 CIRCUIT – TNV-3 CIRCUIT B7 f B8 d B9 d e
earthed SELV CIRCUIT – TNV-2 CIRCUIT
– TNV-3 CIRCUIT
B10 d
B11 d e TNV-2 CIRCUIT – unearthed TNV-1 CIRCUIT
– earthed TNV-1 CIRCUIT
– TNV-3 CIRCUIT
B12 d e
B13 d e f
B14 f TNV-3 CIRCUIT – unearthed TNV-1 CIRCUIT
– earthed TNV-1 CIRCUIT
B12 B13 d SUPPLEMENTARY basic-insulated conductive
part or ELV CIRCUIT
– double-insulated conductive part – unearthed SELV CIRCUIT
S1 b
S1 b TNV CIRCUIT – basic-insulated conductive part
– ELV CIRCUIT
S2 d
S2 IEC 60950-1 : 2005
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Table 2H (concluded)
Location of insulation Grade of
insulation between and Figure 2H Key to
SUPPLEMENTARY
or REINFORCED
unearthed HAZARDOUS VOLTAGE SECONDARY CIRCUIT
– double-insulated conductive part – unearthed SELV CIRCUIT
– TNV CIRCUIT
S/R1 c
S/R1 c
S/R2 c REINFORCED PRIMARY CIRCUIT – double-insulated conductive part
– unearthed SELV CIRCUIT
– TNV CIRCUIT R1 R1 R2 earthed HAZARDOUS VOLTAGE SECONDARY CIRCUIT
– double-insulated conductive part – unearthed SELV CIRCUIT
– TNV CIRCUIT
R3 R3 R4 The term "conductive part" refers to an electrically conductive part that is
– not normally energized, and
– not connected to any of the following: • a circuit at HAZARDOUS VOLTAGE, or
• an ELV CIRCUIT, or • a TNV CIRCUIT, or • an SELV CIRCUIT, or • a LIMITED CURRENT CIRCUIT.
Examples of such a conductive part are the BODY of equipment, a transformer core, and in some cases a conductive screen in a transformer.
If such a conductive part is protected from a part at HAZARDOUS VOLTAGE by:
– DOUBLE INSULATION or REINFORCED INSULATION, it is termed a "double-insulated conductive part"; – BASIC INSULATION plus protective earthing, it is termed an "earthed conductive part";
– BASIC INSULATION but is not earthed, that is it has no second level of protection, it is termed a "basic-insulated conductive part".
A circuit or conductive part is termed "earthed" if it is connected to a protective earthing terminal or contact in such a way as to meet the requirements in 2.6 (although it will not necessarily be at earth potential). Otherwise the circuit or conductive part is termed "unearthed".
a For requirements for FUNCTIONAL INSULATION, see 5.3.4.
b The WORKING VOLTAGE of the SUPPLEMENTARY INSULATION between an ELV CIRCUIT or a basic-insulated
conductive part and an unearthed accessible conductive part is equal to the most onerous WORKING VOLTAGE
for the BASIC INSULATION. The most onerous WORKING VOLTAGE may be due to a PRIMARY CIRCUIT or
SECONDARY CIRCUIT and the insulation is specified accordingly.
c Insulation between an unearthed SECONDARY CIRCUIT at HAZARDOUS VOLTAGE and an unearthed accessible
conductive part or circuit (S/R, S/R1 or S/R2 in Figure 2H) shall satisfy the more onerous of the following: – REINFORCED INSULATION whose WORKING VOLTAGE is equal to the HAZARDOUS VOLTAGE; or
– SUPPLEMENTARY INSULATION whose WORKING VOLTAGE is equal to the voltage between the SECONDARY CIRCUIT at HAZARDOUS VOLTAGE and
• another SECONDARY CIRCUIT at HAZARDOUS VOLTAGE,or • a PRIMARY CIRCUIT.
These examples apply if:
– there is only BASIC INSULATION between the SECONDARY CIRCUIT and the PRIMARY CIRCUIT; and – there is only BASIC INSULATION between the SECONDARY CIRCUIT and earth.
d BASIC INSULATION is not always required (see 2.3.2.1 and 2.10.5.13). e The requirements of 2.10 apply, see also 6.2.1.
f The requirements of 2.10 do not apply, however see 6.2.1.
IS 13252 (Part 1) : 2010 IEC 60950-1 : 2005
60950-1 IEC:2005 – 185 – F6 B4 F5 F4 F2 F11 F7 F7 F8 F9 R2 S2R4 S/R2c) R1 S1R3 S/R1c) S R B B1 B1 R2 S2R4 S/R2c) R2 S2R4 S/R2 c) R2 S2R4 S/R2c) S/R B B B3 B6 B6 B2 B5 B5 B6 F3 B F F1 F B B7 f) B F10 F13 B B8 B12 B12 B11 d)e) B9 e) B14 f) B B13 d) B13 d)e) B10 d) F F12 R f) f) f) e) PRIMARY CIRCUIT TNV-2 CIRCUIT Unearthed TNV-1 CIRCUIT
Earthed SELV CIRCUIT
Similar circuit or conductive part
B: BASIC INSULATION S/R: see Footnote c in Table 2H F: FUNCTIONAL INSULATION
S: SUPPLEMENTARY INSULATION R: REINFORCED INSULATION
TNV-3 CIRCUIT Earthed TNV-1 CIRCUIT Unearthed SELV CIRCUIT
or double-insulated conductive part ELV CIRCUIT or basic-insulated conductive part Unearthed HAZARDOUS VOLTAGE SECONDARY CIRCUIT Earthed HAZARDOUS VOLTAGE SECONDARY CIRCUIT IEC 1550/05
NOTE The references c), d), e) and f) refer to the corresponding footnotes in Table 2H.
Figure 2H – Examples of application of insulation
2.9.4 Separation from hazardous voltages
Where accessible conductive parts, including SELV CIRCUITS, TNV CIRCUITS and their related windings, are separated from parts at HAZARDOUS VOLTAGE, the following constructions are
permitted. The insulation, including each element of DOUBLE INSULATION, shall be rated for the WORKING VOLTAGE, or if applicable the REQUIRED WITHSTAND VOLTAGE, between the parts. The
different methods of separation fall into three groups, methods 1, 2 and 3.
a) (Method 1) DOUBLE INSULATION or REINFORCED INSULATION providing permanent separation,
assured by barriers, routing or fixing; or
b) (Method 1) DOUBLE INSULATION or REINFORCED INSULATION on or between the parts to be
separated; or
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c) (Method 1) DOUBLE INSULATION, consisting of BASIC INSULATION on one of the parts to be
separated and SUPPLEMENTARY INSULATION on the other part; or
d) (Method 2) BASIC INSULATION on the part at a HAZARDOUS VOLTAGE, together with protective
screening connected to the main protective earthing terminal in accordance with 2.6.1 b); or
e) (Method 3) BASIC INSULATION on the part at a HAZARDOUS VOLTAGE, together with connection of the other part to the main protective earthing terminal in accordance with 2.6.1 b), such that the voltage limits for the accessible part are maintained by relative circuit impedances or by the operation of a protective device; or
f) any other construction providing equivalent separation.
NOTE 1 For examples of other constructions providing equivalent separation, see Table 2H and Figure 2H.
For e), it is permitted to protect a circuit by earthing a part other than the protected circuit itself, for example, the secondary winding of a transformer supplying the protected circuit.
NOTE 2 The consequences of the circuit possibly being earthed at a second point, for example, by connection to other equipment, should be considered.
Compliance is checked by inspection.
2.10 Clearances, creepage distances and distances through insulation