Accurate current measurements for individual circuits are important in terms of control. On this basis, you can assess the current condition of the cables and the machines connected to them. However, it is often the case that network parameters make it difficult to determine current or voltage, especially in the case of large production machines. Fortunately, current transformers effectively increase the measurement range. How? More about this in the article below. We also indicate the five best models available in our wholesaler. Check for yourself if one of them will also work in your case.
Check current transformers at the Onninen wholesaler
What are current transformers?
If a large current flows through a circuit, it may be difficult to measure it with standard ammeters . Therefore, current transformers are used in such situations. These are small transformers. On the primary side, there is usually a single wire passing through the measurement hole, which means that there is only one turn on this side. However, the number of secondary turns (N 2 ) is specified on the transformer housing. This structure allows for measuring a larger value on the secondary side (I 2 ) by reading the current value on the primary side (I 1 ). The value you are looking for can be calculated from a simple relationship:
I 1 =I 2 *N 2
Devices of this type are used to increase the measuring range of ammeters or galvanically separate measurement and protection circuits from the main current path.
The most important parameters of current transformers
When choosing a measuring transformer, 
you should pay attention to some of its main parameters, such as:
- Rated primary current I pn . This value refers to the measuring circuit.
- Rated secondary current Isn . This value must be adapted to the working circuit.
- Gear ratio, i.e. the ratio of secondary to primary current. In most cases, it results directly from the number of turns on the secondary side. The actual gear ratio is not equal to the rated gear ratio - therefore this first value must be corrected.
- Measurement error. The final measurement error is influenced by the sum of measurement errors resulting from individual measurement stages. It results from the phase error, current error and accuracy class of the device.
- The highest allowable voltage of the device.
Knowing all the mentioned parameters, you can easily match the appropriate current transformer model to a given electrical circuit. However, the choice of manufacturer may be questionable - on the market you can find both recognizable brands and completely unknown companies producing electrical parts.
The best models of current transformers in the Onninen wholesaler
Onninen electrical wholesaler cooperates with 
the best producers. Therefore, below we present five proven and reliable current transformers that will completely meet your requirements.
ETI CTE-80 toroidal transformer
The advanced ETI CTE-80 transformer will work well in large industrial plants. It does not require calibration and at the same time has a high accuracy class, which ensures very accurate and safe measurements. The toroidal structure allows you to measure circuits with various loads. At the same time, very low heat on the primary side allows the transformer to be connected to machines operating in continuous mode.
Fanina ISS-1 current transformer
In the case of the Fanina ISS-1 current transformer, we have a gear ratio of 500:5. The device has already been calibrated and is immediately ready for use. The apparent power is 5 AV, which is quite a low value. It is also worth paying attention to the accuracy class of 0.5, which ensures very accurate measurements.
Current transformer with open F&F core
Another current transformer with excellent parameters is the F&F 150-5A class 1 open-core current transformer designed for 150 A systems. The 150:5 ratio allows for a significant increase in the measurement scale. The apparent power, however, is only 3 AV.
Hager SRA 01505 current transformer
Another model designed for 150 systems 
A. In the case of the Hager SRA 01505 current transformer, it is worth paying attention to its high accuracy class at a relatively low price. Low apparent power on the measuring side is perfect for automatically controlled systems.
Schneider Electric DIN 150/5 current transformer
It does not require calibration and at the same time provides very high measurement accuracy (class 0.5). The Schneider Electric DIN 150/5 current transformer is also distinguished by its low price and high level of reliability. That is why it is still our favorite model of this type of measuring equipment.