> ## Documentation Index
> Fetch the complete documentation index at: https://docs.voltview.co.uk/llms.txt
> Use this file to discover all available pages before exploring further.

# Electricity meters

> What a site meter measures, and how that feed sits in VoltView.

VoltView already treats the **import MPAN** as the source of truth for what a site buys from the grid. This section explains what that meter is actually counting, so consumption, peak demand, and bill validation read the same way.

<CardGroup cols={2}>
  <Card title="Energy and power" icon="bolt" href="/metering/energy-and-power">
    kWh, kW, kVA, kvarh, and power factor — the quantities on a commercial bill.
  </Card>

  <Card title="Demand and capacity" icon="gauge-high" href="/metering/demand">
    Maximum demand, MIC, load factor, and diversity across a portfolio.
  </Card>
</CardGroup>

## What the meter is for

A kilowatt-hour is the energy used by 1,000 W running for one hour. That is the **unit** on an electricity bill.

The meter does not store a list of appliances. It measures instantaneous voltage and current, multiplies them to get instantaneous power, and integrates that over time to energy. Traditional meters only keep a running total. **Smart meters** keep the same total and also store usage in settlement intervals (typically **half-hourly** in GB) and send it back to the supplier.

That interval record is what makes time-of-use and day/night registers possible. A cumulative register alone cannot tell you *when* the energy was used.

## How it sits in VoltView

```
Site
├── Meters (import MPAN, optional export MPAN)
│   ├── Register reads (TOTAL, DAY, NIGHT, PEAK, OFF_PEAK)
│   └── Interval consumption (smart / supplier HH)
├── Solar systems
└── Batteries
```

| Feed            | What it answers                                                                         |
| --------------- | --------------------------------------------------------------------------------------- |
| Register read   | Opening and closing index on the face of the meter                                      |
| Interval series | kWh (and, where the meter records them, kvarh / kVAh) in each settlement period         |
| Invoice         | What the supplier billed for those same quantities                                      |
| On-site assets  | Generation and storage next to the import MPAN — see [On-site assets](/assets/overview) |

Interval data and the register are not two truths. Over a clean period, the sum of interval kWh should match `current reading − previous reading`, after any [billing multiplier](/metering/energy-and-power#billing-multiplier).

## Traditional vs smart

|                     | Traditional (index only)                                 | Smart / HH                                                 |
| ------------------- | -------------------------------------------------------- | ---------------------------------------------------------- |
| What you get        | A cumulative kWh (and sometimes kvarh) register          | The same registers, plus half-hourly (or better) intervals |
| How a bill is built | Closing read − opening read, often estimated             | Settlement data, or a smart read marked as such            |
| Time-of-use         | Only if the meter has more than one register (day/night) | Intervals can be rated by time of day                      |
| VoltView source     | `MANUAL`, `INVOICE`, `CUSTOMER`                          | `SMART_METER`, `SUPPLIER_API`                              |

A smart read is still a register value. It is not a substitute for the interval series when you need a load curve or a peak.

## How the meter is connected

Most VoltView sites are one of these. You do not need the wiring diagram; you do need to know which case you are in, because it changes the multiplier and the capacity.

| Arrangement                                        | Typical site    | What to watch                                                                                                              |
| -------------------------------------------------- | --------------- | -------------------------------------------------------------------------------------------------------------------------- |
| Single-phase, whole current                        | Small supplies  | One import MPAN, no CT ratio                                                                                               |
| Three-phase, whole current                         | Smaller C\&I    | Still no CT; the meter sees line current directly                                                                          |
| Three-phase with **CTs** (and sometimes VTs / PTs) | Larger C\&I, HV | The face reading is not billed kWh until you apply the [billing multiplier](/metering/energy-and-power#billing-multiplier) |

Whole-current meters are installed in the load circuit. CT-metered supplies step current (and on HV, voltage) down so the meter itself is a standard 5 A / 110–120 V instrument. The ratio is printed on the meter or the CT chamber, and again on the invoice.

## What this is not

* A catalogue of historic meter movements (induction discs, electrolytic cells, clock meters). Those are how older hardware worked. VoltView does not model them.
* A field-test or calibration manual. Accuracy disputes go to the supplier and the meter operator, not into a VoltView correction factor.
* Gas. Gas uses an MPRN, a correction factor, and a calorific value. That is a different conversion, documented on the invoice fields, not here.