Current transformers
In principle, the choice of current transformer for the EL34xx is not critical. The internal resistance within the current circuit of the EL34xx 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 EL34xx, but may lead to small measuring inaccuracies.
 | Measuring transformers Suitable measuring transformers for use with the energy and power measuring terminals are available with the SCT series from Beckhoff. |
Accuracy
Please note that the overall accuracy of the set-up consisting of EL34xx and current transformers to a large degree depends on the accuracy class of the transformers.
| No approval as a billing meter Even an arrangement with a current transformer of class 0.5 or better is not subject to approval and certification. The EL34xx is not an approved billing meter within the meaning of the standard for electricity meters (DIN 43 856). |
Notice | |
DC currents with the EL3453 DC currents can lead to saturation of the internal current transformers and thus to measurement errors! |
Current types
The EL34xx can measure any current type up to a limiting proportion of 400 Hz. 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.
Overcurrent limiting factor FS
The overcurrent limiting factor FS of a current transformer indicates at what multiple of the primary rated current the current transformer changes to saturation mode, in order to protect the connected measuring instruments.
Notice | |
Attention! Risk of damage to the device! The EL34xx-xxxx must not be subjected to continuous loads that exceed the current values specified in the technical data! In systems, in which the overcurrent limiting factors of the transformers allow higher secondary currents, additional intermediate transformers with a suitable ratio should be used. |
Notice | |
Attention! Risk of damage to the device! The EL3453-xxxx must not be permanently loaded with more than I1 + I2 + I3 + IN = 20 A total current across all channels! |
Protection against dangerous touch voltages
During appropriate operation of the EL34xx 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 EL34xx
- General insulation fault
| |
Risk of electric shock! The complete wiring of the EL34xx 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 EL34xx allows a maximum voltage of 480 V for normal operating conditions. The conductor voltage on the current side must not exceed this value! For higher voltages, an intermediate transformer stage should be used!
An EL34xx is equipped with a protection impedance of typically 1.2 MΩ on the voltage measurement side. 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.
Connection cable for current transformers
Please note the following minimum power values for current transformers to be connected:
| Rated secondary transformer current | |||||||
|---|---|---|---|---|---|---|---|---|
| 1 A | 1 A | 1 A | 1 A | 5 A | 5 A | 5 A | 5 A |
Cross-section | 0.5 mm² | 1 mm² | 1.5 mm² | 2.5 mm² | 0.5 mm² | 1 mm² | 1.5 mm² | 2.5 mm² |
1 m | 0.3 | 0.2 | 0.2 | 0.2 | 2.4 | 1.3 | 0.9 | 0.6 |
2 m | 0.4 | 0.3 | 0.3 | 0.2 | 4.6 | 2.4 | 1.7 | 1.1 |
3 m | 0.5 | 0.3 | 0.3 | 0.3 | 6.8 | 3.5 | 2.4 | 1.5 |
4 m | 0.6 | 0.4 | 0.3 | 0.3 | 9.0 | 4.6 | 3.1 | 2.0 |
5 m | 0.6 | 0.4 | 0.3 | 0.3 | 11.2 | 5.7 | 3.9 | 2.4 |
10 m | 1.1 | 0.6 | 0.5 | 0.4 | 22.2 | 11.2 | 7.5 | 4.6 |
20 m | 2.0 | 1.1 | 0.8 | 0.6 | 44.2 | 22.2 | 14.9 | 9.0 |
30 m | 2.8 | 1.5 | 1.1 | 0.7 | 66.2 | 33.2 | 22.2 | 13.4 |
40 m | 3.7 | 2.0 | 1.4 | 0.9 | 88.2 | 44.2 | 29.5 | 17.8 |
50 m | 4.6 | 2.4 | 1.7 | 1.1 | 110.2 | 55.2 | 36.9 | 22.2 |
100 m | 9.0 | 4.6 | 3.1 | 2.0 | 220.2 | 110.2 | 73.5 | 44.2 |
Cable length | Minimum operating load in VA for current transformers with copper cables and 80 °C operating temperature | |||||||
Additional measuring devices in the current circuit
Please note that the addition of additional measuring devices (e.g. ammeters) in the current circuit can lead to a significant increase in the total apparent power.
Furthermore, connection IN of the EL34xx must represent a star point for the three secondary windings. Additional measuring devices therefore have to be potential-free and must be wired accordingly.