Everyone is probably familiar with electric energy meters. Nowadays, smart meters are often used to measure and bill household electricity. If you look closely, you will find that there is a parameter 5 (60) written in the prominent position of the electric energy meter.

For example, the parameter in the red circle in the picture above: 5 (60) A. Looking at the unit, we know that it is written as current, so what is the relationship between these two currents? What happens when the current is exceeded? Let’s talk about what the two currents refer to according to the outside brackets (5) and inside the brackets (60).
Current in brackets
The current in parentheses – 60A in the example, refers to the maximum rated current of the energy meter. Different from other equipment, the rated current of the electric energy meter is greatly affected by environmental factors, so a certain margin is generally left when it leaves the factory – the actual maximum rated current is 120% of the marked current. Therefore, if the number in parentheses is 60, its maximum rated current is 72A – if it is not a particularly harsh environment, the impact on the maximum rated current will generally not reach 20%. Therefore, the maximum rated current of a meter marked with 60A is generally about 66A in actual use.
What happens when this value is exceeded? The answer is inaccurate measurements – maybe more, maybe less.
Current outside brackets
The 5 outside the parentheses here is called the basic current, also called the calibration current. It is determined by the starting current of the electric energy meter – the minimum current value that allows the electric meter to continuously rotate and continuously measure. The starting current of a general smart meter is 0.4% of the rated current. That is, a meter with a rated current of 5A will be charged as long as the current in the circuit reaches 0.02A when in use. There will be a ratio between the rated current and the maximum rated current, such as 5 (60) A, which is a 4 times relationship. This ratio is called “load width”. Generally, there are 2 times, 4 times, 6 times, 8 times or even more than ten times – the larger the load width, the stronger the technical level required, and the price of the meter will naturally be higher.
Therefore, the numbers outside the parentheses have little to do with the actual use by the user—more or less than this value will not affect the metering of the meter. There are mainly two aspects affected by the calibration current: the price of the meter (related to the load width) and the starting current (calculated by the calibration current).