What Is a 2-In 2-Out Test Terminal Block? Uses and Selection Criteria
A 2-in 2-out test terminal block is a DIN rail terminal block with two push-in connection points on each side, used as a check point in the control panel.
A 2-in 2-out test terminal block is a DIN rail terminal block with two push-in connection points on each side, used as a check point for control and signal circuits in a panel. Its connection layout is the same as a 2-in 2-out terminal block: four points in one housing. It marks where measurements are taken during commissioning, periodic maintenance and fault finding.
The name "test terminal block" does not describe a single design. Whether the circuit can be disconnected at the terminal block without removing conductors varies from type to type, and the product data of the models in the catalog does not state a disconnect mechanism. So the first question in selection is whether measurements will be taken with the circuit closed or with the circuit disconnected.
Test, disconnect and measuring terminal blocks compared
| Type | What it does | Typical use |
|---|---|---|
| 2-in 2-out terminal block | Joins four points at the same potential | Distributing supplies and common terminals |
| 2-in 2-out test terminal block | Same four points; housing intended for testing | Check point in control and signal circuits |
| Knife disconnect terminal block | Opening the knife separates the two sides | Disconnecting a circuit without removing conductors |
| Measuring and disconnect terminal block | Offers test probe connection along with disconnection | Meter and measuring circuits |
Selection criteria
- Need to disconnect: If you need to open the circuit at the terminal block, confirm in the manufacturer's data sheet that a disconnect mechanism is present, or choose knife disconnect or measuring and disconnect terminal blocks, whose product descriptions state disconnection explicitly.
- Measuring point: Check in the data sheet which opening of the terminal block takes the meter probe or test plug, and the suitable probe diameter.
- Total current: The Onka OPK test terminal blocks in the catalog have a rated current of 24 A, and this value applies to all four points together; the sum of the circuit currents must not exceed it.
- Conductor size and connection: The product name says 2.5/4 mm². Check the connectable cross-section and stripping length in the data sheet. The OPK series uses push-in spring connection; to remove a conductor, press the release button with a screwdriver.
- Housing color: Eight colors are available. Marking test points with a separate color makes it easier to find the right terminal block during maintenance.
Common mistakes
- Using it in a current transformer secondary circuit: If the secondary circuit of a loaded current transformer is opened, a dangerously high voltage appears at its terminals. These circuits use measuring terminal blocks that can short-circuit the secondary before disconnecting it; confirm this feature in the data sheet of the product you choose.
- Assuming every test terminal block disconnects the circuit: Without a disconnect mechanism, conductors must be removed to measure; decide on the need at the start.
- Exceeding the total current: 24 A applies to the whole terminal block, not to each point.
- Connecting two separate circuits to the same terminal block: Without an isolating link all four points are at the same potential; separate circuits need separate terminal blocks.
Related standards
- IEC 60947-7-1: Sets construction and test requirements for DIN rail terminal blocks for copper conductors; OPK test terminal blocks are listed against this standard.
2-in 2-out test terminal blocks in the catalog
The 2-In 2-Out Test 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 test terminal block | 24 A, 750 V | gray `1020265`, beige `1020266`, black `1020267`, blue `1020268`, brown `1020269`, red `1020270`, yellow `1020271`, green `1020272` |
Frequently asked questions
What is a test terminal block used for?
It marks the point where measurements are taken in control and signal circuits and makes the conductors easier to reach during commissioning, maintenance and fault finding.
Can the circuit be disconnected at a test terminal block?
It depends on the type. The product data of the models in the catalog does not state a disconnect mechanism; if you need to open the circuit, confirm it in the data sheet or choose a knife disconnect or measuring and disconnect terminal block.
Can a test terminal block be used in a current transformer circuit?
It is not recommended. A current transformer secondary must not be left open under load; these circuits use measuring terminal blocks that can short-circuit the secondary.
What is the difference between a test terminal block and a 2-in 2-out terminal block?
On models without an isolating link the connection layout is the same, with all four points at the same potential; check in the data sheet whether there is an isolating link. The test terminal block is used as a check point in the circuit, the standard 2-in 2-out terminal block for distribution.