Socomec Distribution Accessories: Busbars, Cage Terminals, Fuse Bases

At a Glance. Socomec does not only sell breakers, fuse gear and transfer switches — it also supplies the parts that hold a switchboard together. This guide covers the 242 Socomec items that sit under distribution accessories: the insulated CU.SPLE.ISO copper busbar plates, cage terminals rated 200 A to 600 A, RM and RMS fuse bases on 10×38, 14×51 and 22×58 bodies, the DIRIS Digiware RJ45 bus and D-70 gateway, and the P15 / P30 auxiliary supplies. Getting these right is what decides whether a panel is merely assembled or actually rated.

1. What Counts as a Distribution Accessory

Panels are usually specified from the protective devices downwards: a main switch disconnector, a set of fuse combination switches, some surge protection, and a current measurement chain. The accessories are what remain — and they are what most often gets substituted at the last minute, usually with something that fits but is not rated for the duty.

The Socomec accessory range under Distribution Accessories falls into six practical groups:

• Busbar plates and insulating barriers — the CU.SPLE.ISO family, supplied in 2 m lengths
• Cage terminals — the connection points where outgoing cables land on the busbar system
• Fuse bases and neutral tubes — RM and RMS carriers for cartridge fuses
• Busbar supports and connection blocks — SB and SBC parts that anchor and extend the bars
• DIRIS Digiware wiring — RJ45 bus cables, the D-70 display and gateway, USB configuration leads
• Auxiliary power supplies — the P15 and P30 24 V DC modules that feed measurement and control

None of these devices protects anything on its own. Their job is to carry current, hold a bar in place, or carry data. That makes them easy to overlook and, unfortunately, easy to get wrong. A cage terminal selected for the wrong conductor range will not close on the cable; a busbar plate that is too thin will run hot at rated current; an RJ45 bus cable that is the wrong length will leave the D-70 gateway outside its segment limit.

2. Insulated Busbar Plates: The CU.SPLE.ISO Family

The CU.SPLE.ISO parts are insulated copper busbar plates supplied in 2 m lengths. The order code reads as a stack: the first figure is the number of bars in the set, followed by the bar width and thickness in millimetres. CU.SPLE.ISO.3X32X1 is therefore a three-bar set of 32 mm × 1 mm bars, while CU.SPLE.ISO.8X40X1 is an eight-bar set of 40 mm × 1 mm bars.

Why the bar cross-section matters more than the ampere rating

A busbar does not have a nameplate current. Its current-carrying capacity comes from the cross-section, the permissible temperature rise, the ambient temperature inside the enclosure and how well the bar can shed heat. A 32 mm × 1 mm bar and a 100 mm × 1 mm bar are both copper and both 2 m long, but they are not interchangeable at the same current.

That is why the CU.SPLE.ISO range steps in width rather than in a stated amperage. The 32 mm set suits modest distribution inside a small enclosure; the 100 mm set is intended for the main horizontal run of a larger assembly where several hundred amperes have to be distributed across a row of fuse bases and terminals. Increasing the number of bars in the set does not raise the current rating of each bar — it increases the number of independent circuits that can be run on the same support.

Insulation is a mechanical function, not just a safety one

In an uninsulated busbar system the phase-to-phase clearance is set by the support spacing and by the geometry of every terminal on the run. Any change to a terminal or a tap-off forces the clearance to be re-checked. Insulated plates remove most of that work: the insulating layer is part of the bar, so the clearance is fixed by the product rather than by the assembly. This is the single biggest reason panel builders standardise on insulated bars for retrofit and extension work, where the original clearances may no longer be documented.

3. Cage Terminals: Poles, Current and Conductor Range

A cage terminal is a clamped connection point. A cable is inserted into a cage and a screw or bolt compresses a pressure plate onto the conductor. There is no lug to crimp and no torque-sensitive cable shoe, which makes cage terminals the default choice for aluminium as well as copper conductors and for on-site termination where a crimping tool may not be available.

Read the pole count and the conductor count separately

The two numbers in the reference are not the same thing, and confusing them is the most common ordering error in this family. The pole count tells you how many independent phases or circuits the terminal block can grip. The conductor count tells you how many cables can be landed on each pole.

A six-pole, two-conductor terminal such as the 600 A version accepts two cables per pole — twelve cable entries in total, distributed across six circuits. A four-pole, one-conductor terminal accepts a single cable per pole. If an incoming feeder has to be doubled up to reach the required cross-section, the single-conductor version will not do it, no matter how high its current rating.

Conductor range in MCM and in mm²

Most Socomec cage terminals are specified in MCM, the American circular-mil convention, while the double cage terminal is specified in square millimetres. This is not a conversion artefact — the two families were designed for different markets and the mechanical cage is sized accordingly. A range of 6…300 MCM corresponds broadly to 16…150 mm², and 4…600 MCM to roughly 25…300 mm². If a project is specified in square millimetres, check the cage against the actual cable, not against a conversion table, because the flexible-conductor case is the one that catches people out: a fine-stranded flexible cable needs a wider cage than the same nominal area in solid or stranded form.

4. Fuse Bases and Neutral Tubes

Fuse bases hold the fuse link and provide the two contacts that put it in series with the circuit. Socomec's RM and RMS carriers cover the three standard European cartridge bodies — 10×38, 14×51 and 22×58 — in one-, three-, four-pole and three-pole-plus-neutral versions. The RMS designation identifies a carrier with a fuse-blown indicator; RM is the plain version.

Match the base to the fuse, then the fuse to the circuit

A 22×58 body is not a bigger 14×51: the two have different breaking capacities at a given current and, more importantly, different available fuse-link ranges. Choosing the base first and then hunting for a link that fits is backwards. Decide the utilisation category and the rated current from the load, then confirm the body size, then order the carrier. If the circuit is a motor feeder, the link will be an aM type; if it is cable protection, a gG type. The companion guide to Socomec fuse selection works through those categories in detail.

Neutral tubes are not optional extras

On a three-phase-plus-neutral distribution board the neutral is a current-carrying conductor and it needs the same short-circuit protection as the phases. A neutral tube lets the neutral link sit alongside the phase links on the same carrier pitch. Leaving the neutral out, or protecting it with a smaller body than the phases, is a mistake that shows up only during a fault.

5. DIRIS Digiware Wiring: RJ45 Bus and the D-70 Gateway

The measurement side of a Socomec assembly is the DIRIS Digiware system. Current sensors and voltage modules are daisy-chained on a dedicated bus, and the D-70 provides the local display and the protocol gateway to the building or SCADA system.

The D-70 is a 96 × 96 mm panel instrument that carries RS485, Ethernet, Digiware and USB ports and speaks Modbus RTU, Modbus TCP, SNMP v1/v2/v3 including traps, BACnet IP, HTTP(S), FTP(S) and SMTP(S). In a mid-size switchboard it is usually the only head-end device needed — the bus runs from module to module, the D-70 terminates it, and the Ethernet port carries everything upstream.

Bus cables are a system part, not general-purpose patch leads

The yellow RJ45 cables in this range are Digiware bus cables. They carry the module-to-module supply as well as data, and the bus has a maximum length and a maximum number of modules. Using a generic Ethernet patch lead of the same length may work on the bench and fail in the panel, because the conductor gauge and the pairing are not the same. Because the modules sit at a fixed pitch along a DIN rail, the short lengths matter as much as the long ones: a 0.10 m jumper between two adjacent modules keeps the cable from looping back across the terminals.

The 50 m drum with 100 field connectors exists for the case where the run length is only known on site. It is the practical answer for retrofits, where the modules are already mounted and the bus has to be made to measure. If the measurement chain also includes current transformers, the companion guide to current transformer selection explains how ratio, class and VA burden are chosen before the wiring is run.

6. Auxiliary Power Supplies for the Measurement Chain

A DIRIS gateway, a set of trip units and a few signalling relays need a 24 V DC rail. Socomec supplies two compact modules for exactly this duty, and choosing between them is a simple sum of the standing currents in the panel.

Size on standing current, not on peak

These are auxiliary supplies, not control-power transformers. The load is dominated by standing currents: a display draws continuously, an Ethernet interface draws continuously, and a trip unit draws continuously even when nothing is happening. Add those up, add the inrush of any relay coils, and leave headroom. What you must not do is size the module from the panel's main rating — a 630 A switchboard may genuinely need only 15 W of auxiliary power.

7. Busbar Supports, Connection Blocks and Pre-Cut Links

Once the bars are cut to length they have to be supported at intervals, joined where they change direction, and tapped where a fuse base or a terminal is mounted. The SB and SBC parts cover that work.

• SBC10 4P 1x10+2x10MM FIX.350MM — a four-pole connection block for 10 mm bars at a 350 mm fixed pitch
• SB P 30 4 POLES — a four-pole support for the 30 mm bar family
• SB 306 UNIP + insulating plate — a single-pole support supplied with its insulating plate
• SB E 44 4P ESCALIER — a stepped four-pole support for offset bar runs
• 2 CA OF DE PRECOUPURE MONTE — pre-cut link set with terminals already fitted

These parts are usually ordered after the main scheme is drawn, and they are usually ordered by eye. The pitch is the number that matters: a fixed 350 mm pitch block sets the support spacing for the whole run, and every terminal added afterwards has to fit within it. Where the panel is a retrofit of an existing assembly, the pre-cut links are the fastest route, because the cutting and the termination are already done.

8. Current Rating and Thermal Checks

An accessory is rated as part of an assembly, not on its own. IEC 61439 is the standard that governs this, and it is the reason a supplier can only give a current rating for a terminal in the context of a tested combination.

Three checks cover most of the risk:

• Bar cross-section against current and ambient. A bar sized for 40 °C inside the enclosure will not carry the same current at 55 °C, and derating is not optional in a hot plant room.
• Terminal cage against the actual conductor. The cage must close on the cable that arrives on site, including the flexible case and any doubling up. A 600 A terminal with a 2…60 MCM (2x) range is designed for two parallel conductors per pole; using it with one small cable wastes the capacity without gaining anything.
• Fuse base against the prospective short-circuit current. The base must be able to withstand the let-through energy that the chosen link permits. Matching body size is necessary but not sufficient.

None of these checks needs a specialist program. They need the load schedule, the ambient temperature inside the enclosure and the cable schedule to be available at the same time as the accessory list — which is exactly the point at which most accessory orders are placed from memory.

9. How the Accessories Fit Together

A typical Socomec distribution assembly with all six accessory groups in play looks like this:

Read top to bottom, this is also the order in which the parts should be specified. The bus run sets the geometry, the fuse bases and terminals set the tap-off pitch, and the measurement chain is laid out along whatever is left. Doing it in the other order — buying the terminals first and then trying to find a bar that reaches them — is how accessory lists turn into second orders.

10. Ordering Checklist

Before releasing an accessory order, confirm each of the following against the drawing:

• Bar set — number of bars, width and thickness, matched to the current and to the ambient inside the enclosure
• Terminal poles and conductors — read as two separate numbers, with the conductor range checked against the cables that will actually arrive
• Fuse base body and poles — 10×38, 14×51 or 22×58, plain or with indicator, plus the matching neutral tube
• DIRIS bus length — total run plus jumpers, counted against the maximum bus length for the number of modules
• Gateway ports — which upstream protocol is actually needed: Modbus RTU, Modbus TCP, SNMP traps, or BACnet IP
• Auxiliary power — sum of standing currents, with headroom, not the panel's main rating

Send us your bar sizes, the outgoing cable schedule, the fuse body you have chosen and the protocol the building management system expects, and we will confirm the exact Socomec order numbers within 24 hours. Start from the quotation form, or browse the full Socomec range and the wider fuses and circuit protection group if the protective devices themselves still need to be selected.

Distribution accessories are the least glamorous part of a switchboard and the part most likely to be chosen from a catalogue page without a second look. They are also the parts that decide whether the assembly is rated or merely assembled — and unlike the breakers, they are cheap enough that getting them right costs almost nothing.