An NMI is a unique 10-11 digit registration number that represents a 'grid connection point' to your electrical supply site. For most intents and purposes it is also your meter number and account identifier, because the vast majority of sites only have one grid connection point and each electrical supply account is paired to an NMI.
Why do NMIs sometimes alternate between 10 and 11 digits?
The first 10 digits are all that is needed to identify your site and the 11th simply provides assurance that the right number has been used. This is because the 11th is a 'check sum' value that makes sure there's no typo in the first 10.
The check sum is the product of a complicated mathematical formula that uses the first 10 digits to produce an additional 11th digit. If the check sum enters fails to correspond with what the formula calculates should have been produced, then industry staff will know that a mistake has been made.
How does my NMI relate to other numbers I have been given?
Customers sometimes have multiple sites. Each site usually has one NMI (i.e. grid connection point), although it is not impossible to have more. At each grid connection point there may be one or more electrical meters depending on the site's electrical requirements. Each of these meters will monitor the electrical usage of one of more of your electrical devices, depending on how your site's electrical wiring has been set up.
Ultimately, all of your electrical use will be recorded on electronic 'registers,' which are used to invoice your account(s). You can download your registers if you wish, although they are very complicated files that the lay person will not be able to read.
Some example setups are displayed in the mock up below. Note that for the register codes, 'E' means 'grid-to-site' export and 'B' means 'site-to-grid' export.
