DIN Rail Terminal Blocks Selection Guide

DIN rail terminal blocks come in screw, spring and hybrid connection types; choose by connection type, level count and measuring or test needs.

This guide explains what to check when selecting products in the DIN Rail Terminal Blocks category.

DIN rail terminal block types

• Screw connection terminal blocks: Onka MRK series. Besides single-level types, two-level (MRK-Ç), three-level (MRK-3K) and motor terminal block (MRK-MT) models are in this group.
• Standard terminal blocks: Onka OPK spring connection single-level terminal blocks and Gwest DIN rail mounted terminal blocks.
• Hybrid connection terminal blocks: Onka HRK series; one end is a screw connection and the other end is a spring connection.
• 1-in 2-out and 2-in 2-out terminal blocks: These are spring connection OPK types; three or four connection points are at the same potential, which serves to multiply a line without using a separate jumper.
• 2-in 2-out test terminal blocks and knife disconnect system terminal blocks: For measuring and test connections. The manufacturer calls the knife type a disconnect and test terminal block; the circuit is opened with the knife on the terminal block.
• Busbar, lug-connected and covered terminal blocks: A large-cross-section conductor is bolted on with the cable lug on its end; the connection point is covered with a cover.
• Tap-off terminal blocks: Two types for MRK 35-50 mm² and 70-95-120 mm² terminal blocks; used to tap off with a smaller cross-section from a large-cross-section terminal block. In the Onka data, the connection cross-section is 16 mm² and the current is 76 A.

How to read rated cross-section, current and voltage

The mm² value in the product name is the terminal block's rated cross-section. The current values in the manufacturer data for Onka MRK single-level terminal blocks are as follows:

• 1.5 mm²: 17.5 A
• 2.5 mm²: 24 A
• 4 mm²: 32 A
• 6 mm²: 41 A
• 10 mm²: 57 A
• 16 mm²: 76 A
• 35 mm²: 125 A

For OPK single-level terminal blocks, the same current values are stated for the same cross-sections. The voltage value is given as 750 V for these types and 1000 V for lug-connected covered types. For multi-level and multi-input models, also check the current field on the product page separately.

These are the terminal block's rated values; the conductor cross-section and the protective device are determined by the project calculation. For a preliminary check you can use the cable current carrying capacity calculation tool.

The difference between screw, spring and hybrid connection

Screw connection (MRK). The conductor is clamped by screw pressure. In the Onka data, the tightening torque is 0.4 Nm for MRK 2.5 mm², 0.8 Nm for 6 mm² and 2 Nm for 16 mm²; it increases as the cross-section grows.

Spring connection (OPK). A spring holds the conductor; no screw is tightened. In push-in spring terminal blocks, a solid or ferruled conductor is inserted by pushing, without a tool; to insert a flexible conductor without a ferrule and to remove a conductor, the release point on the terminal block is pressed.

Hybrid connection (HRK). Because one side of the terminal block is a screw connection and the other side a spring connection, the wiring inside the panel and the field cable can be connected with different techniques.

Parts needed for a terminal block row

• Rail: In the Onka manufacturer data, the terminal block height is given separately for 35/7.5 and 35/15 rails; when calculating panel depth, take the value for the rail used. Rails are in the DIN rails category.
• Row length: End stops and separator plates are added to the product of terminal block width and quantity. The width of an Onka MRK terminal block is 5.9 mm for 2.5 mm², 8.15 mm for 6 mm² and 12 mm for 16 mm².
• End stops and terminators: Secure the terminal blocks on the rail at both ends of the row.
• Terminal block top jumpers: Connect adjacent terminal blocks to the same potential; selected by terminal block cross-section and number of poles (such as 2-way, 4-way, 10-way).
• Separator plates and markers: These are in the other subgroups of the same accessory category; ground terminal blocks with yellow-green housings are in a separate category under Terminal Blocks.

Order notes

• Each housing color is a separate stock code (gray, beige, black, blue, brown, red, yellow, green); the colors are listed with consecutive codes (such as MRK 2.5 mm² gray 1010012, beige 1010013).
• Lug-connected covered, hybrid, tap-off and knife terminal blocks, and some of the screw connection terminal blocks, are listed as made-to-order; for made-to-order products the lead time is confirmed before the order.
• You can reach the relevant color directly by typing the Onka product code into the site search.

Frequently asked questions

What is the difference between MRK and OPK DIN rail terminal blocks?

Both are Onka DIN rail terminal block series. MRK is screw connection: the conductor is clamped with a screw, and the large cross-sections in this category are in this series. OPK is spring connection: a spring holds the conductor instead of a screw. In hybrid terminal blocks with the HRK code, one end is a screw connection and the other end a spring connection. When selecting end stops, top jumpers and separator plates, look at the series name in the product name.

How many amperes does a 2.5 mm² DIN rail terminal block carry?

In the manufacturer data for the Onka MRK 2.5 mm² screw connection and OPK 2.5 mm² spring connection DIN rail terminal blocks, the current is 24 A and the voltage is 750 V. This is the terminal block's rated value. The current to be used in the circuit, the conductor cross-section and the protective device are determined by the project calculation.

What is a hybrid DIN rail terminal block and where is it used?

A hybrid DIN rail terminal block has one connection end with a screw and the other end with a spring connection. It is used in panels where the wiring inside the panel is to be connected to the spring side and the cable coming from the field to the screw side. In this category the Onka HRK series is listed in 2.5 mm² and 6 mm² cross-sections; the torque value in the manufacturer data is applied to the screw end.

Why is an end stop fitted at the end of a DIN rail terminal block row?

DIN rail terminal blocks snap onto the rail and are lined up side by side. The end stop is fixed to the rail at both ends of the row and prevents the terminal blocks from sliding along the rail and the row from opening up. Among Onka accessories, small, large, screwless and group-marker end stops for the MRK and OPK series are listed as separate products; the end stops of the mini MPK series are different.

When are two-level and three-level DIN rail terminal blocks preferred?

They are preferred in panels where rail length is limited: a single housing has two or three connection levels stacked on top of each other, so more circuits fit in the same rail length. In return the terminal block height increases and access to the conductors on the lower level becomes harder. In this category there are screw connection two- and three-level models; spring connection multi-level types are in the Spring Connection Terminal Blocks category.

Can a flexible cable be fitted without a ferrule in a spring DIN rail terminal block?

In push-in spring terminal blocks, a solid conductor is fitted by pushing it in directly. When a multi-stranded (flexible) conductor is pushed in without a ferrule, the strands can spread out, so either a ferrule is fitted or the release point on the terminal block is pressed with a screwdriver, opening the spring, and the conductor is inserted. The cross-section range the terminal block accepts for ferruled and unferruled conductors is checked in the manufacturer data.