Gap (i)
The gap, if one exists, between the surfaces of a joint shall nowhere exceed the maximum
values given in Tables 1 and 2.
Where the maximum constructional gap (ic) is less than that required by Table 1 or 2, the value
shall be stated in the certificate and the apparatus shall be marked according to 27.2 item i) of
IEC 60079-0. In addition, this condition for safe use shall be specified in the manufacturer’s
instructions.
The surfaces of joints shall be such that their average roughness Ra (derived from ISO 468)
does not exceed 6,3 μm.
For flanged joints, there shall be no intentional gap between the surfaces, except for quickacting
doors or covers.
For electrical apparatus of Group I, it shall be possible to check, directly or indirectly, the gaps
of flanged joints of covers and doors designed to be opened from time to time. Figure 1 shows
an example of construction for indirect checking of a flameproof joint