Current transformer
In principle, the choice of current transformer for the KL3403 is not critical. The internal resistance within the current circuit of the KL3403 is so small that it is negligible for the calculation of the total resistances of the current loop. The transformers should be able to produce a secondary rated current of 1 A. The primary rated current Ipn can be selected arbitrarily. The common permissible overload of 1.2 x Ipn is no problem for the KL3403, but may lead to small measuring inaccuracies.
Accuracy
Please note that the overall accuracy of the set-up consisting of KL3403 and current transformers to a large degree depends on the accuracy class of the transformers.
 | Approval and certification A set-up with a class 0.5 current transformer cannot be approved or authenticated. The KL3403 is not an approved billing meter according to the electricity meter standard (DIN 43 856). |
Current types
The KL3403 can measure any current type up to a limiting proportion of 2 kHz. Since such currents are frequently created by inverters and may contain frequencies of less than 50 Hz or even a DC component, electronic transformers should be used for such applications. The KL3403 is also available as a special version with an interface for ±20 mA.
Overcurrent limiting factor FS
The overcurrent limiting factor FS of a current transformer indicates at what multiple of its primary rated current the current transformer changes to saturation mode, in order to protect the connected measuring instruments.
Note | |
Please note the rated current! The KL3403 must not be subjected to more than 5 A for a prolonged period of time! For systems in which the over-current limiting factors of the transformers allow secondary currents of more than 5 A, additional intermediate transformers with a ratio of 5A/1A or 1A/5A should be used! |
Protection against dangerous touch voltages
During appropriate operation of the KL3403 with associated current transformers, no dangerous voltages occur. The secondary voltage is in the range of a few Volts. However, the following faults may lead to excessive voltages:
- Open current circuit of one or several transformers
- Neutral conductor cut on the voltage measurement side of the KL3403
- General insulation fault
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Ensure accidental-contact protection! The complete wiring of the KL3403 must be protected against accidental contact and equipped with associated warnings! The insulation should be designed for the maximum conductor voltage of the system to be measured! |
The KL3403 allows a maximum voltage of 500 V for normal operating conditions. The conductor voltage on the current side must not exceed 500 V! For higher voltages, an intermediate transformer stage should be used!
On the voltage measurement side, a KL3403 is equipped with a protection impedance of 500 kΩ. If the neutral conductor is not connected and only one connection on the side of the voltage measurement is live, the resulting voltage against earth in a 3-phase system with a phase-to-phase voltage of 400 VAC is 230 VAC. This should also be measured on the side of the current measurement using a multimeter with an internal resistance of 10 MΩ, which does not represent an insulation fault.
Additional measuring instruments in the current circuit
Please note that the addition of additional measuring instruments (e.g. ammeters) in the current circuit can lead to a significant increase in the total apparent power.
Furthermore, connection IN of the KL3403 must represent a star point for the three secondary windings. Additional measuring instruments therefore have to be potential-free and must be wired accordingly.