Video: Nexus 1500 – Technical guide

Video transcript

How the Nexus 1500+ plus is mounted, wired in star and in delta, powered and connected, and what to check before putting it into service. This is work on live circuits, for qualified staff only: terminals, C Ts and P Ts can all carry lethal voltages. Voltage leads and supply are fused, the C Ts go through a shorting block, and a switch next to the meter acts as its disconnect. And never open a CT secondary with current flowing. The meter goes into a panel cut-out of about 19

by 12 centimetres, horizontally or vertically: for vertical mounting the screens are simply rotated. From behind, 4 brackets snap into the housing and are screwed to the panel, without over-tightening. Everything is wired from the back. On the left, the voltage inputs; next to them Ethernet, IRIGB and the 8 high-speed inputs. Then 4 option slots, with RS-485, a second Ethernet, relays or status inputs.

On the right, the power supply. The current inputs take one or 5 amp C Ts, in 3 ways: on the current gills with a ring lug, passing straight through the meter with the gills removed, or with crimp tabs. Above 10 amps sustained, use pass-through. And keep the C Ts close: the cable is a burden on them. In a four-wire star the meter works with 3 elements, 3 P Ts and up to 4 C Ts. The current circuits come first:

the common of the CT secondaries to earth, then each CT through the shorting block, polarity mark to HI, the other side to LO. The 4th CT, on the neutral, is optional. Now the voltage. The PT secondary common is earthed and taken to V n. Each phase feeds its PT, whose primary returns to the neutral, and the secondaries reach V a, V b and V c through their fuses. Up to 347 volts phase to neutral, the meter can also be connected directly, without P Ts.

In a three-wire delta two elements are enough: C Ts on phases A and C, and two P Ts in open delta, between A and B and between C and B. Their secondary common is earthed and goes to V b, with V n tied to it; V a and V c complete the connection. The meter has its own supply, alternating or direct depending on the option. Earth first, to PEGND. Then neutral or negative to N minus, and line or positive to L plus, through a 4 amp slow-blow fuse.

With the low-voltage DC option the polarity is reversed: follow the label. Ethernet takes a category 5 cable. The front USB port appears to the PC as a serial port, and the optical port takes a magnetic coupler. IRIGB goes plus to plus and minus to minus: a reversed pair is the usual fault. RS-485 is a daisy chain, never a star or a tee, in shielded twisted pair. The shield is earthed at one point only;

then plus to plus, minus to minus and shield to shield, device after device. Up to 31 meters and 1200 metres of cable, with termination only at the ends. The 4 option slots take the cards the application needs, and the meter detects them by itself. With voltage and supply removed, the card slides along its track until it clicks. Then the parameters are reset and the card is configured in the PC software. Before service: check the wiring and power up, connect the PC software, program the CT and PT ratios and the hookup, check the phasors, and set the time source.

Then enable password protection with your own passwords: until you do, the meter is open. The phasor screen is the quickest check. In star, each current sits in phase with its voltage; in delta, 30 degrees from the phase-to-phase voltage. A negative current angle means a reversed CT: short it at the block and swap its leads. Power network analysers, from Amperis.