KROHNE H250 M9 NEPSI Ex nA - Manual (Page 13)

ELECTRICAL CONNECTIONS
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H250 M9
www.krohne.com 03/2013 - 4002616501 AD H250 M9 NEPSI Ex nA R01 en
4.2 Power supply
The variable area flowmeter does not require any separate power supply. The necessary power
for the built-in electrical equipment is supplied via the signal circuits.
4.3 Inputs/outputs
The signal circuits of the variable area flowmeter may only be connected to downstream devices
or circuits that satisfy the requirements of protective extra-low voltage (PELV). The terminal
assignment of the built-in electrical equipment is described in the Standard Installation and
Operation Instructions.
Only circuits that are suitable for operation in Zone 2 hazardous areas may be connected.
Outside of the flowmeter, measures must be taken to prevent the rated voltage from being
exceeded by more than 40% due to temporary faults.
Use a 50 mA microfuse when connecting the signal output (ESK II / ESK2A) to voltage sources
with a possible short-circuit current of more than 100 mA.
4.4 Earthing and equipotential bonding
The variable area flowmeter must be included in the equipotential bonding of the hazardous
area. This is done using the earth connection on the rear of the indicator part.
Shields should be securely connected to the earth potential of the hazardous area, and
connected to the terminal located in the indicator part via the shortest route. In the case of shield
earthing at both ends (e.g. for reasons of electromagnetic compatibility), adequate equipotential
bonding that reliably prevents potential differences is necessary between the two earthed ends
of the shield in order to avoid excessive equalising current.
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