5. Test Basis and Safety Information for Intrinsically Safe Control Circuits (Ex-i)
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MU2B-0375GE51 R0616C
5. Test Basis and Safety
Information for Intrinsically
Safe Control Circuits (Ex-i)
Test Basis: EN60079-11
Ex-i intrinsic safety is based upon the
principle that devices in systems
equipped with an ATEX-certified
switching amplifier require only minimal
voltage and current. Sparks which might
form when the microswitch’s contact is
opened are thus minimized, as a result of
which the surrounding flammable
atmosphere cannot be ignited.
FEMA Ex-I Thermostats are equipped
with gold contact microswitches (except
for those devices featuring internal
interlocking for the purpose of min. or
max. limitation). A blue cable gland, the
Ex-I manufacturer’s plate, and the serial
number identify those pressure switches
suitable for use in intrinsically safe
circuits.
Generally speaking, Ex-I thermostats are
suitable for use in zones 1 and 2 (gas) as
well as 21 and 22 (dust). When equipped
with a category “ia” switching amplifier,
such devices can also be employed on
the process-side in zone 20 (dust) and
zone 0 (gas).