305 Connecting to power supplyVEGAPULS 61 • 4 … 20 mA/HART - two-wire36499-EN-1704055 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.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.Use 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 HART multi-drop mode.Metric threadsIn the case of instrument housings with metric thread, the cableglands are screwed in at the factory. They are sealed with plasticplugs as transport protection.You have to remove these plugs before electrical connection.NPT threadIn the case of instrument housings with self-sealing NPT threads, it isnot possible to have the cable entries screwed in at the factory. Thefree openings for the cable glands are therefore covered with red dustprotection caps as transport protection.Safety instructionsVoltage supplyConnection cableCable glands