DIN rail terminal block types are not interchangeable, and picking the wrong one only shows up months later, when a panel fails inspection or a circuit will not isolate. The decision starts with a simple question: what does this circuit have to do? Once you answer that, the type narrows quickly, and the mechanical and electrical specifications become a checklist rather than a guess.
This guide works through the terminal block families by circuit function first, then maps each one to a product you can order. Every dimension, current figure and torque value below comes from our own published product data.
A DIN rail terminal block is a mounting solution and a connection point at the same time. The rail itself carries no current; it is a standardised 35 mm steel or aluminium strip that holds devices in place. What makes a block the right one is in its internals and its marking. Before you read a single datasheet, list the circuits on your drawing and assign each one a job:
Only after the job is fixed does the mechanical choice matter: how the block mounts, what colour it is, how many ways it has, and what conductor section it accepts. Worked through in order, these DIN rail terminal block types give you a part number rather than a guess.
| Type | Circuit job | How to identify it on the rail | Check before ordering |
|---|---|---|---|
| Feed-through | Joins incoming to outgoing conductor | Plain housing, one or two wire entries per side | Conductor range, rated current |
| Protective earth (PE) | Connects the protective conductor to the earth path | Marked PE, with a metal contact foot onto the rail | PE approval, rail bonding |
| Fuse | Accessible branch-circuit protection | Wider housing with a fuse holder in the face | Fuse format, breaking capacity |
| Disconnect / knife | A deliberate, visible break in the circuit | Lever or knife mechanism in the front | Switching duty, test plugs |
| Multi-level | Stacks two or three circuits in one footprint | Taller housing, two or three rows of entries | Level marking, isolation |
| Sensor / actuator | Organises 24 V DC field I/O wiring | Several conductors per way, often an LED window | PNP or NPN, commoning |
| Multi-conductor / distribution | Shares one potential across several ports | Several outputs from one input | Commoned paths, path rating |
| Component carrier | Holds a diode, LED, resistor or varistor | Extra wide body with a component bay | Component type and rating |
One point is worth stating plainly. Pluggable is not one of the eight. It describes how a module separates from its base for service, and a pluggable terminal can still be feed-through, fused or multi-level. Keep the interface choice separate from the circuit job.
A feed-through terminal is the most common block in any control cabinet. It carries a conductor from one side to the other through an internal metal path, held by a screw, a spring cage or a push-in spring. For ordinary point-to-point power, control and signal wiring it is the right default: there is no reason to pay for a specialised function unless the circuit needs one.
Three parameters decide whether a given block works in your panel. Rated current is the continuous current the internal path carries, not the rating of the breaker feeding it. Rated cross-section is the conductor range the clamping unit accepts: a block that takes 10 to 35 mm² rigid will not accept 2.5 mm² stranded without a ferrule. Short-time withstand current is the peak the path survives, usually expressed as Ipk in kA.
Our screw-type blocks are rated to IEC 60947-7-1, which covers screw-type and screwless clamping units for round copper conductors from 0.2 mm² to 300 mm², in circuits up to 1000 V AC and 1500 V DC. It also sets the dielectric strength, voltage drop, temperature rise and pull-out force requirements. The three parameters above are model-specific: check them on the datasheet for the exact block rather than carrying a figure across from another product.
A compact feed-through style bar in brass with a galvanised iron screw is our NHA22 screw terminal neutral bar with black bracket, running from 6 to 20 ways on a 6 × 9 mm section. For single large conductors, our NHA30 PC series terminal with white cover gives one way per housing from 16 to 120 mm².
A PE terminal block is not a feed-through block with a green housing. It has a metal contact foot that makes a direct electrical and mechanical connection to the DIN rail, and the rail is bonded back to the panel’s main earthing system. That foot is the entire electrical function, and it is why the block is listed under a separate product standard.
PE terminal blocks fall under IEC 60947-7-2, fuse terminal blocks under IEC 60947-7-3, and PCB terminal blocks under IEC 60947-7-4. If a supplier quotes a terminal block without naming a part of the IEC 60947-7 series, ask.
Our PE-side products are colour-identified at the fixing part rather than relying on the housing alone. The NHA04-E earth bar with green fixing part carries a green fixing element, and the NHA27-E screw terminal grounding bar with cover gives you the earth connection with a transparent cover over the screws. For a fully enclosed version, our a fully enclosed variant keeps the conductors completely enclosed.
Note the deliberate difference from the neutral side. A PE block and a neutral block may sit next to each other on the same rail, but they must not be the same block. Our NHA04 neutral bar with blue fixing part is colour-marked blue to keep the two visually distinct, which is the simplest way to stop a miswire during panel build. The wiring rules behind that separation are covered in our guide on putting a ground wire on a neutral bar, and the difference between the two devices in neutral bar versus ground bar.
These two are grouped together because both are wider than a standard block, but they solve different problems and are governed by different standards.
A fuse terminal block integrates a fuse carrier into the terminal, so protection sits at the point of connection rather than in a separate holder. The benefit is serviceability: the fuse changes without disturbing the wiring around it. The parameters that matter are the fuse format, the breaking capacity, and whether a blown fuse is visible from outside the cabinet. IEC 60947-7-3 sets out the safety requirements for this block type.
A disconnect terminal creates a deliberate break in the circuit without removing any conductor, which is what lets a technician verify a circuit is dead before touching it. For current transformer secondary circuits there is a more specialised variant, the test-disconnect terminal, which provides a controlled shorting sequence so the CT is never left open-circuited.
Choose on permitted duty rather than on appearance. A disconnect terminal intended for signal isolation is not necessarily rated for load switching, and the manufacturer data will say which duty the mechanism is approved for.
When rail space is the binding constraint, a multi-level terminal stacks two or three independent circuits vertically, using one footprint instead of two or three. On a control cabinet with dozens of 24 V DC sensor circuits, this is often the difference between fitting the devices inside the enclosure and running out of backplate.
Two things decide whether a multi-level block saves space. Wire access: on a stacked block the conductor has to reach the lower level, which means a deeper enclosure and more bend radius. And level identification, because a miswired lower level is hard to reach and easy to miswire.
Where space is genuinely critical, our NHA29 eight-way insulated strip block takes a different route: it puts eight ways into a single insulating housing, 173 mm long at 16 mm² and 270 mm at 70 mm², so eight conductors share one body instead of eight separate pieces of plastic.
Field I/O wiring is where terminal blocks earn their keep in a PLC cabinet. A three-wire sensor needs a signal, a supply and a return, often with a status indicator. A sensor terminal block packages all of that into one way, so the cabinet keeps a consistent grid rather than a mix of singles and specials.
The critical parameter here is not current, it is sourcing and sinking. A PNP sensor switches the positive side of the supply and a NPN sensor switches the negative side, so a terminal block with an LED wired for one convention will read backwards on the other. Also check the commoning arrangement against your field wiring, and whether shield termination has a dedicated way to leave the block, because improvised shield connections inside the cabinet are a common source of noise problems that end up blamed on the PLC.
A distribution block is not a terminal block with more ways. The topology is different: one incoming conductor feeds many outgoing paths, and the block is rated on the current in that common path and on the fault withstand of the whole assembly. A terminal block that passes each conductor through separately has no shared path to rate.
Our range runs from 80 A to 500 A. The UKK-160A single phase distribution block and the C01-407 125A four phase distribution block cover the mainstream panel sizes. The C01-407 is rated 500 V and 125 A, with a 20 kA impulse withstand, and accepts 10 to 25 mm² rigid conductors on the input side while the output side takes 2.5 to 10 mm² through a separate 5.5 mm entry. Torque on that unit is 2 to 3 Nm.
At the top of the range the construction changes completely. The C02-400A four phase distribution block uses a purple copper conductor with nickel-plated iron screws and M10 stud connections rather than small wire screws, tightened to 8.5 Nm on the input side.
The gap between those two constructions is not a matter of price tiers. Both are rated 500 V and IPk 20 kA, and the real difference sits at the input terminal: the C01 range clamps a conductor of a published size, the C02 range clamps a cable lug on an M8 or M10 stud. C01 vs C02 distribution block sets the conductor ranges, stud sizes and torque values side by side.
Selecting between the two categories is covered in power distribution block versus terminal block, and the current and conductor sizing method is set out in our DIN rail power distribution block guide.
Once the circuit function is settled, mounting is the next axis that changes the part number. Three arrangements are in use and they are not interchangeable.
| Mounting method | How it is fixed | Typical bar section | Trade-off |
|---|---|---|---|
| Screw fixation | Bolted to the backplate through standoffs | 1.5 × 15 to 3 × 25 mm | Lowest cost, no rail needed, but uses backplate area |
| DIN rail snap-on | Clips onto a 35 mm top hat rail | Link bars in brass, 100 A class | Fast to reconfigure, but the rail costs money and takes depth |
| Bridge type | A continuous bar with conductors on raised positions | 1.5 × 15 to 3 × 25 mm | Many ways in one length, easy to extend |
The screw-fixed range is the most economical per way. Our NHA21 neutral bar with white bracket runs from 5 to 12 ways on a 7 × 11 mm section, and the D02 brass bridge type grounding bar is the bridge-side equivalent, with 3 to 15 ways on a 1.5 × 15 mm section.
For DIN rail mounting, our NHA15 neutral bar link screw brass mounted with DIN rail clamps straight onto a standard 35 mm rail. Bridge type is the choice when you want many ways in a short run: our NHA10 bridge type neutral bar with colourised full plastic cover takes 10 to 18 ways in one length. The rail itself is covered in our DIN rail sizes guide.
Colour is the fastest way to identify a function on a crowded rail, and it is standardised under IEC 60445. Green and yellow is reserved for protective conductors, blue identifies the neutral. North American practice under NEMA uses a different phase colour set, which is one reason a panel built to one convention should not be opened by someone working to the other.
There is a rule that catches out experienced installers, and it is written into the product standard. IEC 60947-7-1 clause 7.1.4 states that the green-yellow colour combination is not permitted for marking terminal blocks. The reason is straightforward: green-yellow on a terminal means protective earth, and if every terminal could carry that colour, a green-yellow terminal could be mistaken for a PE connection when it is not one.
This applies to through terminal blocks under IEC 60947-7-1. It does not apply to ground conductor rail-mount terminal blocks approved under IEC 60947-7-2, which are permitted to be green-yellow because they are specifically PE products.
This is the practical reason our PE and neutral products carry colour at the fixing part or the holder rather than relying on housing colour alone. The NHA28 neutral bar with colourised holder and the NHA25 screw terminal neutral bar with cover keep the identification at the point where the conductor actually lands.
Once function, mounting and colour are settled, the sizing is arithmetic. Three numbers determine whether a block physically fits: the number of ways, the maximum conductor section per way, and the overall length on the rail. Our A29 eight-way strip block shows how they interact: the same eight ways are available from 16 mm² to 70 mm², and as the section goes up the body gets longer and wider.
| Model | Ways | Max conductor section | Length | Width |
|---|---|---|---|---|
| A28/16 | 8 | 16 mm² | 173 mm | 24 mm |
| A28/25 | 8 | 25 mm² | 205 mm | 27 mm |
| A28/35 | 8 | 35 mm² | 250 mm | 33 mm |
| A28/50 | 8 | 50 mm² | 260 mm | 35 mm |
| A28/70 | 8 | 70 mm² | 270 mm | 38 mm |
The pattern holds across the range: a higher conductor section means a longer body, so count the length rather than the number of blocks when you work out how many fit, and add the end stops and separation pieces at both ends.
For a single large conductor, our NHA30 series gives one way per housing with a length that tracks the section directly, from 16 mm at 16 mm² to 120 mm at 120 mm². The A29 strip block covers the multi-conductor side.
The housing material sets the operating temperature range, and this is where a nominally identical part number can fail on a hot panel. Our blocks fall into three groups.
All three families carry CE and RoHS certification, and the relevant performance standard is IEC 60947-7-1 with a rated voltage range of 250 to 450 V.
The temperature difference is not academic. A block rated to 65 °C in a panel sitting in a 50 °C ambient has only 15 K of headroom, and current capacity falls as temperature rises — the same derating logic that applies to every other component in the cabinet.
Not on a through terminal block. IEC 60947-7-1 clause 7.1.4 prohibits the green-yellow combination for marking terminal blocks so it cannot be confused with a protective earth connection. Ground conductor rail-mount terminal blocks approved under IEC 60947-7-2 are the specific case where it is permitted. On a standard block, mark the connection with the IEC 60417-5019 protective earth symbol or the letters PE.
Count the conductors that land on that group in the wiring schedule, then add the positions you want to reserve for future circuits. Do not count devices, count conductors. Our neutral bar size chart sets out the full sizing sequence.
It needs to be at least the load current, and checked against the conductor section you are actually using. A block rated 125 A fed by 6 mm² copper is limited by the cable, not by the block. Our brass versus copper neutral bar comparison covers how conductor material changes the practical outcome.
The rated voltage range matters more for DC than for AC, because a DC arc does not self-extinguish at a current zero the way an AC arc does at 50 Hz. Our screw terminal blocks are rated 250 to 450 V, and the standard distinguishes rated voltage from rated impulse withstand voltage, which is where the AC and DC difference shows up in the data.
Mechanically, blocks on the same rail profile fit side by side. The practical constraints are accessory compatibility, depth, and the end stop and separator sizes matching the housing. If you want one accessory system across a panel, specifying a single family for the whole rail is safer.
Three checks in order. Look for the PE marking or protective earth symbol on the housing. Look for the metal contact foot that bonds the block to the rail, which a neutral block does not have. And check the colour of the fixing part or holder: on our range PE products carry a green fixing element and neutral products a blue one, so the identification survives even when the housing colour is not visible from the front.
Function, mounting, colour and section are four independent decisions, and the part number you order falls out of them. The order matters: change the mounting method after you have fixed the function and you will be re-ordering blocks.
Our range covers screw-fixed, bridge type and DIN rail mounted arrangements in brass, with way counts from 3 to 20 and conductor sections from 1.5 × 15 mm to 120 mm². Send a panel schedule and we will specify the terminal block line items against it.
