Accurate current measurements for individual circuits are of great importance in terms of control. On this basis, you can assess the current condition of the wires and the machines connected to them. However, it often happens that network parameters make it difficult to determine the current or voltage, especially in the case of large production machines. Fortunately, current transformers effectively increase the measurement range. How? More on this in the article below. We also indicate the five best models available in our wholesaler. Check for yourself whether one of them will not work in your case.
Check current transformers at the Onninen wholesaler
What are current transformers?
If a large current flows through the circuit, its measurement with standard ammeters may be difficult. Therefore, in such situations, current transformers are used. These are small transformers. On the primary side, there is usually a single wire passing through the measuring hole, which means that there is only one turn on this side. On the other hand, the number of secondary turns (N 2 ) is specified on the transformer housing. This design allows for the measurement of a larger value on the secondary side (I 2 ) by reading the current value on the primary side (I 1 ). The required value 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 to galvanically separate measuring and protection circuits from the main current path.
The most important parameters of current transformers
When selecting 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 I sn . This value must be matched to the operating circuit.
- The ratio is the ratio of the secondary current to the primary current. In most cases, it results directly from the number of turns on the secondary side. The actual ratio is not equal to the rated ratio - therefore, the first value must be corrected.
- Measurement error. The final measurement error is influenced by the sum of measurement errors resulting from the individual measurement stages. It results from the phase error, current error and the accuracy class of the device.
- Highest permissible voltage of the device.
Knowing all the above parameters, you can easily match the right model of current transformer to a given electrical circuit. However, the choice of manufacturer may raise doubts - 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
The electrical wholesaler Onninen cooperates with 
the best manufacturers. That is why we present below five proven and reliable current transformers that will fully meet your requirements.
Toroidal transformer ETI CTE-80
The advanced ETI CTE-80 transformer will prove useful in extensive industrial plants. It does not require calibration, and at the same time it is characterized by a high accuracy class, which ensures very accurate and safe measurements. The toroidal construction allows measuring circuits with different 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 Fanin ISS-1 current transformer, we are dealing with a 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 low. It is also worth noting the accuracy class of 0.5, which ensures very accurate measurements.
F&F Split Core Current Transformer
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 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 the 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 ensures 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 invariably our favorite model of this type of measuring equipment.