# How do prepaid electricity meters work?

## You have always wondered how you get electricity from a 20 digits token? Here is what you need to know about prepaid electricity meters.

Have you always wondered how you get electricity from a 20 digits token? Here is the answer.

### 1) Understand how electricity consumption is calculated

The monthly electricity consumption is calculated based on KWH – Kilowatt Hour.  One Kilowatt (or 1 Unit) is equal to 1000 watts. A standard globe used in a house is 100 Watts. If that globe is to burn for one hour it will consume 0.1 KWH (or units) of power (100 Watts / 1000). If that same globe were to burn for 24 Hours it would therefore use 2.4 KWh or 2.4 Units of electricity.

Your prepaid electricity meter is able to count the flow of electricity used in KWH. The meter balance decreases as you use electricity. The red LED on the meter flashes as electricity is used: the faster it flashes, the more units are being used.

### 2) How is the number of units calculated?

When you request an electricity token, the request is sent to the municipality’s vending system. The vending system checks the tariff applicable to the meter and convert the Rand amount into a specific number of units. Note that most municipalities apply the inclined block tariff, whereby the more you buy within a given month, the more you pay per unit. More on the tariffs here.

### 3) What happens when I enter the token into the meter?

In South Africa, most prepaid electricity meters use the STS technology (Standard Transfer Specification). It means that most prepaid meters accept the same code, a 20 digit encrypted code, which prevents fraudulent vouchers from being generated. This code is then transformed by a software inside your prepaid electricity meter into a token. This token is understood by the prepaid meter as an amount of electricity units (KWH).

### 4) What happens when I forget to top up my meter?

When meter balance reaches zero, the meter switches off the electricity that powers your house. Indeed, the prepaid electricity meter has a relay (an automatic switch) which disconnects the power when there is no units left. When you top up, the meter balance increases and the relays lets electricity flows again.

To help you make sure you always have units, Powertime has developed a virtual meter which estimates the number of units left in your meter. When your meter balances reaches 50 units, Powertime sends a push notification and an email to remind you to top up. Note that the virtual meter is an estimate based on your consumption patterns and on seasonal variations. Read more about Virtual meter.