What Is a 2-In 2-Out Terminal Block? Uses and Selection Criteria
A 2-in 2-out terminal block is a DIN rail terminal block with two connection points on each side, joining four conductors at the same potential.
A 2-in 2-out terminal block is a DIN rail terminal block with two connection points on each side, joining all four points at the same potential. On one side it takes the incoming supply and the conductor that continues to the next point; on the other, the conductors going to two loads, all in one housing. There is no need to jumper two standard terminal blocks for the same job, and each conductor gets its own connection point.
Where is it used?
- Common supplies and returns: Distributing the positive or negative of a 24 V DC control supply, the neutral or a common terminal to several devices.
- Sensor and actuator connections: Supply and common points where two conductors meet on the field side and two on the panel side.
- Continuing a line: Connecting, next to the incoming conductor, a separate conductor that carries the same potential on to the next device.
How it differs from similar terminal blocks
| Type | Connection points | Difference |
|---|---|---|
| 1-in 2-out terminal block | 3 | 1 point on one side, 2 on the other |
| 2-in 2-out terminal block | 4 | 2 points on each side, all at the same potential |
| 2-in 2-out test terminal block | 4 | Same connection layout; test housing used as a check point in the circuit |
The words "in" and "out" only describe which side the connection points are on; the terminal block does not distinguish the direction of current.
Selection criteria
- Number of connection points: This terminal block is enough when up to four conductors meet at the same potential. If you need more points, join several terminal blocks with plug-in top jumpers.
- Total current: The Onka OPK models in the catalog have a rated current of 24 A, and this value applies to all four points together. The conductor on the supply side carries the sum of all the distributed currents; the total must not exceed 24 A.
- Conductor size and type: The product name says 2.5/4 mm². Check the manufacturer's data sheet for the minimum and maximum connectable cross-section for solid, stranded and ferrule-fitted conductors, and for the stripping length.
- Connection technology: The OPK series uses push-in spring connection. Solid or ferrule-fitted conductors are inserted without tools; to insert a fine-stranded conductor without a ferrule, or to remove any conductor, press the release button with a screwdriver.
- Housing color: Color does not change the electrical ratings. Blue housings are commonly used for neutral terminal blocks; separating groups such as the positive and negative of a control supply by color makes wiring and fault finding easier.
Common mistakes
- Assuming 24 A per point: If the currents of two or three loads add up to more than 24 A, you need a larger terminal block or a separate supply.
- Connecting two different circuits to the same terminal block: The four points are joined internally. Two separate potentials need two separate terminal blocks or a double-level terminal block.
- Putting two conductors into one connection point: This terminal block exists to give each conductor its own point. If you plan to use twin ferrules, confirm that the manufacturer's data sheet allows them.
- Using a green-housing terminal block for the protective conductor: A green housing is only a marking color. The protective conductor (PE) goes to a green-yellow protective conductor terminal block (IEC 60947-7-2) that contacts the rail.
Related standards
- IEC 60947-7-1: Sets construction and test requirements for DIN rail terminal blocks for copper conductors; this product group falls within its scope.
- IEC 60445: Identification of conductors by color; blue is for neutral, green-yellow for the protective conductor.
2-in 2-out terminal blocks in the catalog
The 2-In 2-Out Terminal Blocks category has 8 active products; all are from the Onka OPK series and differ only in housing color:
| Series | Ratings | Color and SKU |
|---|---|---|
| Onka OPK 2.5/4 mm² | 24 A, 750 V | gray `1020275`, beige `1020276`, black `1020277`, blue `1020278`, brown `1020279`, red `1020280`, yellow `1020281`, green `1020282` |
Frequently asked questions
What is a 2-in 2-out terminal block used for?
It joins four conductors at the same potential. For example, it is used to distribute a control supply to two separate devices together with the incoming and continuing line.
Can each connection point carry 24 A?
No. 24 A is the rated current of the whole terminal block; the conductor on the supply side carries the total current of the outputs.
Can two different circuits be connected to a 2-in 2-out terminal block?
No. All four points are at the same potential. Two separate circuits need two separate terminal blocks or a double-level terminal block.
What if more than four conductors must meet at the same point?
Place as many terminal blocks side by side as needed and join them with a plug-in top jumper. Check the manufacturer's data sheet that the jumper fits the terminal block series.