Terminal Blocks Selection Guide
A terminal block connects conductors to each other or to a device by screw, spring or clamping connection. DIN rail, spring-connection and fused types.
What is a terminal block? A terminal block is a connecting element used to connect electrical conductors safely to each other or to a device by screw, spring or clamping connection. There are DIN rail terminal blocks lined up on a mounting rail inside the enclosure, splice terminal blocks used in installations, and special types such as fused, ground or disconnect. A terminal block is chosen according to the cross-section of the conductor and the current it will carry.
This guide explains what to look at when choosing products in the Terminal Blocks category.
Terminal block types and where they are used
- DIN rail terminal blocks: Screw-connection, spring-connection and hybrid terminal blocks lined up on a mounting rail inside the enclosure. In the large cross-section types, the conductor is bolted on with a lug at its end.
- Spring connection terminal blocks: Two-level and three-level spring types; used to fit more circuits into the same length of rail.
- Mini terminal blocks: Onka MP and MPK spring-connection terminal blocks with a small housing; the MP series appears as push-in in the product name.
- Fused terminal blocks: They have a fuse holder in the housing; used to protect control and measuring circuits individually. In the Onka product data the current rating is given as 6.3 A.
- Measuring and disconnect terminal blocks: Used to disconnect the circuit at the terminal block and take measurements without dismantling it; there are types with and without test probes.
- Ground terminal blocks: Protective conductor terminal blocks with a green-yellow housing, lined up in the terminal block row.
- Panel ground terminal blocks and panel neutral terminal blocks: Perforated bars and multi-terminal blocks that gather many conductors at a common point. Onka product names give the number of holes, the current rating and the size (such as 12 holes, 250 A, 15x10 mm).
- Junction box terminal blocks: Plug-in and tabbed terminal blocks for splicing conductors inside a junction box.
Barrier terminal blocks and spring push-button terminal blocks are also in separate subgroups.
The difference between screw, spring and junction box type connections
In a screw connection a screw tightens the conductor; the tightening torque is taken from the manufacturer's data. In this category, large cross-section terminal blocks are screw or lug connected.
In a spring connection there is no screw; spring pressure holds the conductor. Mini terminal blocks and the multi-level types in the Spring Connection Terminal Blocks group have this construction.
Junction box terminal blocks have two constructions. In the plug-in type, the stripped conductor is pushed into the socket; the Isıso product data gives 0.5-2.5 mm² for solid conductors and 1.5-2.5 mm² for stranded conductors. In the tabbed type, the lever is lifted, the conductor is inserted and the lever is closed; in the Gwest and Konsan product data the conductor range is 0.2-4 mm².
Values to look at when choosing a terminal block
- Rated cross-section and current. The mm² value in the product name is the rated cross-section of the terminal block; the current rating increases with the cross-section. For Onka screw-connection DIN rail terminal blocks, 24 A is given for 2.5 mm² and 76 A for 16 mm². You can make a preliminary check of the circuit current with the current and fuse calculation from active power tool; the exact values belong to the project calculation.
- Voltage. The value varies by terminal block type: most Onka DIN rail terminal blocks state 750 V, and Gwest plug-in junction box terminal blocks state 250 V. The value in the product data must cover the circuit voltage.
- Color. The green-yellow housing is used for the protective conductor and the blue housing for neutral; the other colors serve to tell phase, control and signal groups apart in the terminal block row.
- Conductor end. A stranded conductor is connected to a screw terminal block with cable ferrules, and to a bolted terminal block with cable lugs.
- Row parts. For a DIN rail terminal block row, end stops, jumper bars, separator plates and labels are ordered separately; these are in the terminal block accessories and spares category.
Brands in this category
- Onka: DIN rail, spring-connection, mini, fused, measuring-disconnect and ground terminal blocks, as well as panel ground terminal blocks, jumper bars, end stops and separator plates.
- Gwest: Plug-in junction box terminal block, multi-purpose (tabbed) terminal block and DIN-rail-mounted terminal block.
- Konsan: Tabbed junction box terminal block, barrier terminal block and spring push-button terminal block.
- Isıso lists a junction box terminal block and a terminal block cover part, TP Elektrik a ground and neutral terminal block, and Çetinkaya Pano a tabbed junction box terminal block.
Order notes
- A significant share of Onka products is listed as made to order; for these products the lead time is confirmed at the time of the order.
- Gwest and Isıso junction box terminal blocks are sold by the pack (box): the number of packs is entered in the quantity field; check the pack contents on the product page.
- You can find a product directly by typing Onka's seven-digit product code (such as 1010012) into the site search.
Terminal block comparison table
| Terminal Block Type | Connection Technology | Cross-Section Range | Application Area | Product Group |
|---|---|---|---|---|
| DIN-rail terminal block (Feed-through / PE / Fuse) | Screw or spring / push-in | 1.5 mm² – 240 mm² | Structured conductor termination in distribution and PLC panels | DIN-Rail Terminal Blocks |
| Junction box connector (Lever / Push-wire) | Tool-free spring lever or push-in | 0.2 mm² – 6 mm² | Fast splicing inside junction boxes and lighting luminaires | Junction Box Connectors |
| Barrier / strip terminal block (Polyamide / Ceramic) | Screw brass insert | 2.5 mm² – 35 mm² | General wiring, appliance terminal boxes, and high-heat zones | Strip Terminal Blocks |
Frequently asked questions
What is the difference between a screw terminal block and a spring terminal block?
In a screw terminal block the conductor is clamped by screw pressure, and the screw must be tightened to the manufacturer's torque; in this category, large cross-section terminal blocks are screw or lug connected. In a spring terminal block a spring holds the conductor, no screw is tightened and the connection time is shorter. The choice is determined by the conductor cross-section, whether the conductor is solid or stranded, and the terminal block series used in the enclosure.
Which terminal block is used inside a junction box?
For splices inside a junction box, plug-in or tabbed junction box terminal blocks are used. The deciding factors are the number of conductors to be joined (such as 2, 3 or 5 poles), the conductor cross-section, and whether it is solid or stranded. The product data of Isıso plug-in terminal blocks gives 0.5-2.5 mm² for solid conductors and 1.5-2.5 mm² for stranded conductors; for tabbed types the range is 0.2-4 mm². The size of the junction box is chosen according to the number of terminal blocks.
What is the difference between a ground terminal block and a panel ground terminal block?
A ground terminal block is a single terminal block with a green-yellow housing, lined up in a DIN rail terminal block row, and connects the protective conductor of one circuit; the product name includes a cross-section value such as 2.5 mm² or 16 mm². A panel ground terminal block is a perforated bar that gathers many protective conductors at a single point; the product name includes the number of holes and the current rating (for example 12 holes, 250 A).
What is a bolt-connection terminal block?
In a bolt-connection terminal block the conductor is bolted to the busbar of the terminal block with a cable lug crimped on its end; it is used for large cross-section power cables. In this store this type is in the busbar, lug-connected and covered terminal blocks group under the DIN rail terminal blocks. The products come in cross-sections such as 35 mm², 95 mm² and 240 mm², and the connection point is covered with a cover.
How is the current rating of a terminal block selected?
The rated current of the terminal block must not be lower than the continuous current of the circuit it will be connected to; the value increases with the rated cross-section. The manufacturer data of Onka screw-connection DIN rail terminal blocks states 24 A for 2.5 mm², 41 A for 6 mm² and 76 A for 16 mm². This is the rated value of the terminal block; the circuit current, conductor cross-section and protective device are determined by the project calculation.