Page 223 - Electrical Installation in Hazardous Area

General requirements for explosion protected apparatus 1 87

temperature class, and then ensure that the surface does not exceed the
following temperatures in service:

T1 - ignition temperature minus 50 "C
T2 - ignition temperature minus 50 "C
T3 - ignition temperature minus 50 "C
T4 - ignition temperature minus 25 "C
T5 - ignition temperature minus 25 "C
T6 - igrution temperature minus 25 "C
A system of temperature classification similar in concept to this existed in
Germany and the relationship between this and the current system is shown
in Table 8.2. In the United States of America there was initially a system
whereby apparatus classification (their equivalent of grouping) determined
the maximum apparatus temperature (see Table 8.1) but in recent years they
have adopted a variation on the European temperature classification system
(see Table 8.2).

Table 8.2 European temperature classification system and its relationship
with German and US systems

Temperature European Historic US systems
system German
system Current Historic
(Note 1) (Note 2) (Note 3) (Notes 3 and 4)

450 "C T1 G1 T1 (842°F) Groups A, B, C and D
300 "C T2 G2 T2 (572 "F) Groups A, B, C and D
T2A (536°F) Groups A, B, C and D
Group C
T2B (500 OF)
Group C
T2C (446 OF)
T2D (419°F) Group C
200 "C T3 G3 T3 (392 OF) Group C
T3A (356°F) Group C
-
T3B (329 OF)
T3C (320°F) -
135 "C T4 G4 T4 (275 @F)
T4A (248 OF)
100 "C T5 G5 T5 (212°F)
85 "C T6 T6 (185°F)
Notes:
1 The UK did not have a temperature classification system prior to the introduction of the
European system.
2 The historic German system did not have the equivalent of T6.
3 The USA works on the Fahrenheit scale but the basic T classes are equivalent.
4 The original US temperature classification was associated with its grouping system whereby
the following was the case: Groups A and B were associated with a maximum temperature
of 536 "F Group C was associated with a maximum temperature of 356 "F.