Metering Guide
Private Sub-Meter vs Separate
Smart Meter
Understanding the difference between a private sub-meter and a separate smart meter is critical when deciding how to manage electricity for a granny flat.
What is a private sub-meter?
A private sub-meter is a device installed behind the main property meter. It records the electricity usage of the granny flat, allowing the homeowner to calculate how much power the secondary dwelling is using. However, there is still only one official electricity account for the entire property. The homeowner receives the bill, pays it, and then informally requests reimbursement from the tenant based on the sub-meter reading.
What is a separate smart meter (NMI)?
A separate smart meter generally establishes an independent National Metering Identifier (NMI) for the granny flat. This can mean the flat has its own connection point and electricity account. The occupant may be able to choose a retailer and receive a bill based on their setup.
Which should you choose?
Private sub-meters are often cheaper to install but can require ongoing administrative effort to calculate bills, and can cause disputes if rates change. A separate meter (NMI) generally requires more upfront electrical preparation and network compliance, but can provide a structured separation for formal tenancy agreements. You should always seek advice based on your specific property and tenancy situation.