# Connection diagram of test box with current transformers

When connecting three-phase consumers, metering devices for measuring the consumed electric energy can be used both directly and with current and voltage transformers. This applies to both active and reactive energy meters. Next, we will tell you how to connect a test box with current transformers to the meter.

## What is important to know

Requirements for devices and switching circuits are indicated in GOST. Manufacturers cannot depart from these requirements, since metering devices must be certified accordingly and pass state verification. So, for example, according to clauses 4.1 and 4.2 of GOST 31818.11-2012 (IEC 62052-11: 2003), standard and allowable voltage and current values ​​are determined for direct and transformer connection meters. The most commonly used in 0.23 and 0, 4 kV networks are direct-connected meters and transformer-connected meters with current transformers. Voltage transformers are usually used in electrical installations with a higher voltage level.

Direct inclusion counters according to the specified GOST have standard values ​​of currents of base and rated currents of 5, 10, 15, 20, 30, 40, 50 A and permissible values ​​of currents are 25, 80, 100 A.

For current transformer meters, the standard current values ​​are set to 1, 3, 5 A. The permissible current values ​​for such meters are 0.2; 0.3; 0.6; 1.0; 1.5; 2.0; 2.5; 5.0; 10.0 A.

What does the standard and permissible current value mean? The standard value of the base current is used for meters with direct connection - it is the initial one to establish the requirements for this type of meters.

The standard value of the rated current is used for meters working through a transformer, and the rated current of the meter must be equal to the rated current of the secondary winding of the current transformer. This requirement is given in clause 1.5.19 of the EMP (Chapter 1.5).

Allowable currents contain a wider range of data. Atchoosing current transformers and counters pay attention to these nuances.

Electricity meters can be turned on using a test box. In PUE p. 1.5.23, it is recommended that metering circuits be constructed for independent assembly of clamps or sections in a common row of clamps. If this is not possible, then test boxes are used for metering circuits. During installation, it is necessary to ensure the shorting of the secondary windings of current transformers when they are checked or replaced. The current circuits of the meters and voltage circuits in each phase must be disconnected without disconnecting the wires and cables.

Without fail, in accordance with the same clause of the PUE, test boxes and clamp assemblies should be able to be sealed.

The design of the KIC should include the ability to connect a reference meter.

## Installation diagram

The figure below shows the electrical circuit for connecting the meter through the test terminal box:

As can be seen from the diagram, a terminal connected to the three-phase power source via current transformers comes to the terminals in the block marked A, B, C. The neutral wire is connected to a separate terminal. Further, from these terminals using the wires connected metering device in compliance with the following conditions:

• transformers are connected according to the star circuit, and their common output is grounded;
• from current converters to the junction box, wires with a cross section of at least 1.5 mm² are laid;
• Three wires with a cross section of 2.5 mm² are connected from the metering device
• for convenience, everything wires are marked - three phases and the beginning of current windings and a general conclusion are indicated.

Since the circuit does not imply direct contact between the terminals of the current transformers and the terminals of the meter, it is necessary to monitor the sequence of switching on.

The counter terminals are connected in the following order:

• A wire from the current winding of the first phase transformer is connected to 1 terminal
• a wire is connected to the second terminal of the meter - voltage of the first phase;
• the wire from the current winding of the second phase is connected to the 4 terminal of the meter;
• 5 connects the voltage of the second phase;
• 7 - incoming wire of the current winding of the third phase;
• 8 - voltage of the third phase;
• 9 - common wire;
• 10 - reserve.

Between the third and sixth terminals, as well as between the sixth and ninth, jumpers are installed in the counter.

For safe counter removal it is necessary to bypass the current circuit to ensure reliable contact between the box screws and the insulated busbar. This bus is located on the rear side and by tightening the screws, as shown in Figure 2, you will ensure contact.

Next, loosen the jumper screws to open the jumpers. After that, remove the jumpers from the power section to disconnect the voltage at the meter terminals. Next, the counter is turned off and off. Connection is in the reverse order.

We also recommend that you watch the video, which clearly demonstrates the various ways of connecting the KIC box to the electricity meter:

We hope that this article was informative and now you know how to connect the test box to the meter. For all questions, please contact the forum or in the comments under the post!

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