Page 320 - Offshore Electrical Engineering Manual

Ex ‘nA’ Non-Sparking 307

TERMINALS

1. The terminals should be installed on 32-mm carrier rail to DIN 46 277/1, each
group being completed by an end section and sandwiched between two end sup-
port brackets.
2. Any cross-connected terminal assembly fitted with jumper bar must be mounted
on the 32-mm carrier rail between insulating partitions.
3. Except when shown in a certificate as being internal wiring of the apparatus, not
more than one single-strand or multiple-strand wire or cable core should be con-
nected into either side of any terminal.
4. Leads connected to terminals should be insulated for the appropriate voltage,
and this insulation must extend to within 1 mm of the metal of the terminal
throat.
5. All terminal screws, whether used or not, must be tightened down.
6. When used in general purpose Ex ‘e’ marshalling junction boxes, the circuits
must be protected by close excess current protection which is designed to oper-
ate within 4 h at 1.5 times the designed load current.
7. The creepage and clearance distances between the installed terminals and
adjacent equipment, enclosure walls and covers must be in accordance with
BS EN 60079-7.

ENCLOSURE

1. Any cable gland or conduit entry into the enclosure must be capable of main-
taining the degree of ingress protection IP54 and must be capable of passing
the 7 Nm impact test required by BS EN 60079-7. If mineral insulated cable is
used, the cable seal must be of a type having component approval for type ‘e’
applications.
2. The installer must ensure that the conductors are not cleated together in such a
manner as to significantly increase the temperature of any individual conduc-
tor. A bunch of conductors at any point in the wiring loom should not contain
any more conductors than are in the multicore cable or conduit from which the
conductors originate.

Other non-hazardous related environmental design limitations are discussed in
PART 5 Chapter 3.

EX ‘NA’ NON-SPARKING
An Ex ‘n’ motor is designed to prevent foreseeable ignition sources in situations, here
the machine is operating within its design parameters in normal operation.
The protection principle limits the maximum temperature of all vital parts of the
machine, and defines measures to prevent sparks. An explosive gas can thus penetrate