Connecting the ZEM voltage reference

To measure power, the Zem needs two things on every phase: current, from its current transformers, and voltage, from its voltage reference. It ships ready to fit: the voltage reference cable comes pre-wired for a four-wire WYE supply, with the Zem set to power itself from it, and the current transformers come pre-calibrated. So on a four-wire WYE system, there's no need to open the enclosure at all.

Connecting it is work for a qualified electrician. Switch off every supply that feeds the panel, including any backfeed, prove it's safe with a properly rated voltage tester, and wear the right protective equipment. Take the reference from the same place the Zem is monitoring, not from another transformer, and not through a UPS. The Zem pairs each voltage with the current on the same conductors, so both must come from the same supply.

Feed it through its own three-phase breaker or fused disconnect. The Zem draws only a few watts, so around one amp per phase is typical, and at least five hundred milliamps: enough to power the meter, while protecting its cable under fault conditions. The final choice is the electrician's. Label it, and keep it within easy reach. And unlike the current transformer cables, the voltage reference cable can be extended.

Inside, it's already wired for four-wire WYE: the three phases to L one, L two and L three, neutral to Ref, and protective earth to P E. A three-wire Delta supply has no neutral, and uses two current transformers. Whichever it is, set the Zem's wiring configuration on the Gateway to match. Each voltage reference pairs with the current transformer on the same phase: L one with CT one, and so on.

As shipped, with its shorting links in, the Zem powers itself from L one and neutral. Its inputs are rated to two hundred and seventy-seven volts line to neutral, and four hundred and eighty line to line. Above two seventy-seven, power it from a separate auxiliary supply, removing shorting links J eight and J nine first. Above four eighty, use voltage transformers, and set their ratio on the Gateway.

Before you close up, check the protection is rated and labelled, the reference comes from the supply being monitored, each phase matches its current transformer, and the wiring configuration is set on the Gateway. Then the Zem reports the voltage on every phase in Edge, and, with its current transformers, accurate power and energy for everything on that supply. ZEM voltage reference. The full installation instructions are at EpiSensor dot com, forward slash documentation.