215 Connecting to power supplyVEGAPULS 66 • 4 … 20 mA/HART - two-wire28438-EN-1709275 Connecting to power supply5.1 Preparing the connectionAlways keep in mind the following safety instructions:Warning:Connect only in the complete absence of line voltage.• The electrical connection must only be carried out by trainedpersonnel authorised by the plant operator.• If overvoltage surges are expected, overvoltage arresters shouldbe installed.Power supply and current signal are carried on the same two-wirecable. The operating voltage can differ depending on the instrumentversion.The data for power supply are specified in chapter "Technical data".Provide a reliable separation between the supply circuit and themains circuits according to DIN EN 61140 VDE 0140-1.Power the instrument via an energy-limited circuit acc. to DIN/EN/IEC/ANSI/ISA/UL/CSA 61010-1, e.g. via Class 2 power supply unit acc. toUL 1310 or an SELV power supply unit with suitable external currentlimitation.1)Keep in mind the following additional factors that influence the operat-ing voltage:• Lower output voltage of the power supply unit under nominal load(e.g. with a sensor current of 20.5 mA or 22 mA in case of fault)• Influence of additional instruments in the circuit (see load values inchapter "Technical data")The instrument is connected with standard two-wire cable withoutscreen. If electromagnetic interference is expected which is above thetest values of EN 61326-1 for industrial areas, screened cable shouldbe used.Make sure that the cable used has the required temperature resist-ance and fire safety for max. occurring ambient temperatureUse cable with round cross section for instruments with housing andcable gland. To ensure the seal effect of the cable gland (IP protectionrating), find out which cable outer diameter the cable gland is suitablefor.Use a cable gland fitting the cable diameter.We generally recommend the use of screened cable for HARTmultidrop mode.Safety instructionsVoltage supplyConnection cable1) Class 2 power supply unit: limited voltage and power level, special insulationagainst circuits with higher voltage. SELV (Safety Extra Low Voltage) powersupply unit: limited voltage level, special insulation against circuits withhigher voltage