Flowserve NRS 1-50 For ONE Electrode - Manual (Page 17)

7
Electrical Connection
- continued -
Explanatory notes to schematic respresentations
Steam boiler plants and (pressurized) hot-water installations according to TRD 604,
EN 12952-07 / EN 12953-06, 72 h operation
Fig. 8
Combination consisting of  level electrode NRG ...-50 and  level switch NRS -50 as water level
limiter. Functional safety IEC 6508, SIL 3.
For operation according to TRD 604, EN 95-07 / EN 953-06 (7 hours), two independent and
separate water level limiters must be used.
Hot water installations require two independent and separate water level limiters. For this purpose
one equipment combination NRG ...-50/NRS -50 shall be installed in the hot-water boiler and the
second one in the pressure maintaining vessel, the expansion tank or the like (depending on the type
of pressurization). For electrically heated steam boilers one water level limiter is sufficient.
Further applications in accordance with national sets of regulations
Fig. 9
Combination consisting of  level electrode NRG ...-50 and  level switch NRS -50 as water level
limiter. The level switch opens two separate safety circuits. Functional safety IEC 6508, SIL 3.
Fig. 10
Combination consisting of  level electrode NRG ...-50 and  level switch NRS -50 as water level
limiter and  level electrode NRG ...-50 /  level switch NRS -50 as low-level pre-alarm.
Functional safety IEC 6508, SIL 3.
Fig. 11
Combination consisting of  level electrodes NRG ...-50 and  level switches NRS -50 as water level
limiter. The level switch opens two separate safety circuits. Functional safety IEC 6508, SIL 3.