Cut a comb busbar only when the exact product is approved for cutting. De-energize and verify the panel is dead, remove the busbar, confirm the required tooth and phase sequence, make a square cut with the manufacturer-approved tool, remove burrs and conductive debris, and enclose the exposed cut end with the matching end cap. Protect any unused live teeth with the specified tooth covers before reinstalling the busbar.
Do not assume every MCB busbar can be shortened. Some product families distinguish between standard non-cuttable busbars and versions specifically designed for cutting. Electrical tape, generic heat-shrink tubing, sealant and an unrelated end cap do not automatically restore the product’s insulation, clearances or documented assembly configuration.
This guide covers insulated pin and fork des peignes de raccordement pour MCB used across compatible modular circuit breakers and related protective devices. It does not cover fabricated switchboard copper bars, busbar trunking or live-work procedures. Cutting and installation should be performed by a qualified electrical worker under the applicable equipment instructions and site safety rules.
Principaux enseignements
- Confirm the exact busbar model is cuttable before marking or cutting it.
- Remove the busbar from the de-energized assembly; do not cut it while installed.
- Determine cut length from the actual device row, tooth geometry and pole sequence—not enclosure width alone.
- Use the cutting and deburring method approved for that product; a saw and file are specified for some systems, but not automatically for all.
- Fit the matching end cap over every cut end that requires protection.
- Use tooth covers for unused live contacts where the system documentation requires them.
- Reject the part if the conductor, teeth or insulation are cracked, distorted, overheated or contaminated.
- Recheck compatibility, seating, phase sequence, terminal tightening and completed-assembly protection before energization.
Before Cutting: Four Pass-or-Fail Checks
The cutting operation begins with documentation, not a saw. Pass all four checks before modifying the part.
| Vérifier | Condition de réussite | Stop condition |
|---|---|---|
| Cutting permission | The exact catalog number or product instructions permit cutting | The documentation is silent, the model is described as fixed length, or cutting is prohibited |
| Row geometry | Tooth type, pitch, terminal depth and device positions match the complete row | The bar only appears to fit, devices have different terminal heights, or teeth do not seat uniformly |
| Electrical layout | Pole sequence, phase arrangement, infeed and required contacts are identified on the assembly drawing | The cut is based only on physical length or would create an unclear phase/neutral arrangement |
| Protection d'extrémité | The correct end cap and any required tooth covers are available for the exact busbar family | The proposed protection is tape, generic heat shrink, sealant or an unmatched accessory |
If the busbar has not yet been selected, use the VIOX Guide de sélection des peignes de raccordement pour disjoncteurs modulaires (MCB) first. Cutting cannot correct the wrong pin or fork interface, pitch, pole arrangement, contact dimensions or electrical rating.
Tools and Parts Required
Use the equipment named in the busbar or distribution-board instructions. A typical controlled work setup may include:
- the exact cuttable comb busbar and its product instructions;
- the matching end cap for the busbar family, pole configuration and conductor profile;
- tooth covers or contact-protection caps where unused teeth remain;
- an approved fine-tooth saw, dedicated busbar cutter or other specified cutting tool;
- a fine file or approved deburring tool;
- a measuring rule, square and non-damaging marker;
- a stable work support or soft-jaw clamp that will not crush the insulation or bend the teeth;
- eye protection, cut-resistant handling protection and other required personal protective equipment (PPE);
- a clean brush or suitable vacuum method for removing metal particles; and
- the specified terminal-tightening tool for reinstallation.
For example, Schneider Electric’s Easy9 consumer-unit instructions tell the installer to use a saw and PPE, then use a file to round the cut ends. That is useful evidence for that equipment system, not a universal tool specification for every comb busbar.
Avoid using side cutters, bolt cutters or pliers as a general cutting method. They can flatten the conductor, split the sleeve, twist the tooth line or leave a sharp, irregular cut. Do not default to an abrasive grinder: heat, sparks and conductive particles can damage insulation or contaminate equipment unless the product procedure explicitly permits that method.
Step-by-Step: How to Cut an MCB Comb Busbar
1. Isolate the supply and verify the assembly is de-energized
Follow the site’s isolation, lockout and verification procedure. Identify every possible source, including alternate supplies where applicable. A switched-off breaker position alone is not proof that the busbar is safe to handle.
Remove the comb busbar from the device row before cutting. This prevents metal swarf from entering breaker terminals, avoids mechanical loading on installed devices and gives the installer clear access to inspect the entire part.
2. Confirm the exact busbar is designed to be cut
Check the catalog number, drawing and installation sheet. Similar-looking products within one range may have different modification rules.
This distinction is especially important when approval status is relevant. Schneider Electric documents both standard UL-recognized comb busbars that must not be cut and separate cuttable versions for a named Multi 9 range. ABB likewise identifies particular busbar families as suitable for cutting and lists matched end-cap part numbers. These examples show why a generic statement such as “all comb busbars are cuttable” is incorrect.
For VIOX products, verify the exact model or drawing before modification. The VIOX de peignes d'alimentation pour disjoncteurs modulaires (MCB) includes pin and fork formats and multiple pole arrangements, but cutting permission and the required accessories remain model-specific.
3. Build the device row and identify the required contacts
Lay out the intended MCBs, residual-current circuit breakers (RCCBs), residual-current circuit breakers with overcurrent protection (RCBOs), isolators or other approved modular devices in their final sequence. Confirm:
- the exact breaker family and terminal interface;
- pin or fork geometry;
- module pitch and any gaps or auxiliaries;
- 1P, 2P, 3P, 4P, 1P+N or 3P+N arrangement;
- phase and neutral sequence;
- infeed position; and
- the number of contacts that will actually engage terminals.
Do not measure only the clear width inside the enclosure. The functional length is controlled by the tooth pattern and the device row. A multiphase busbar also contains a repeating electrical sequence; shortening it must preserve the intended relationship between each tooth and each device terminal.
4. Mark the approved cut position
Transfer the required length to the busbar using the manufacturer’s dimensional drawing or the correctly assembled device layout. Mark a square cut line in an approved blank section between the contacts that must remain.
The finished piece must not contain a half-cut tooth, distorted fork or unsupported conductor section. Allow for the end cap and any clearance stated in the product instructions. Do not create a custom copper projection or strip back the sleeve simply because the cap appears too tight; a poor fit may indicate the wrong cut position or wrong accessory.
Before cutting, perform a second-person or drawing-to-part check on multipole assemblies. A clean cut at the wrong tooth can still connect the wrong phase or neutral position.
5. Support the busbar without deforming it
Secure the part on a clean work surface. Support the conductor close enough to the cut to limit vibration, while keeping pressure away from contact teeth and avoiding damage to the insulation.
The teeth should remain straight, parallel and on the same pitch after the operation. If the clamp leaves marks, crushes the sleeve or changes the tooth alignment, the setup is unsuitable.
6. Make a straight, controlled cut
Use the approved cutting tool and make the cut square to the busbar. Let the tool cut without twisting the part. Excessive force can delaminate or crack the insulation, deform the copper section or bend adjacent teeth.
Where a saw is specified, use a suitable fine-tooth blade and controlled strokes. Where a dedicated cutter is specified, confirm that its capacity matches the busbar profile and conductor section. Do not assume a tool approved for bare copper bar is suitable for an insulated comb busbar.
Stop if the insulation tears along the bar, the conductor folds rather than cuts, or a tooth moves out of alignment. Do not conceal structural damage under an end cap.
7. Deburr the conductor and clean the part
Remove sharp edges and loose burrs using the specified file or deburring tool. The purpose is to leave a smooth end that will not cut the end cap, hold the cap away from its seated position or reduce the intended insulation distance.
Deburring must not materially reduce the conductor section or reshape a nearby contact. Do not file the contact surfaces that enter breaker terminals.
Remove every copper particle and insulation chip from the busbar, work surface and enclosure. Conductive swarf can bridge terminals, damage insulation or remain hidden inside a device opening. Inspect the sleeve for cracks, whitening, cuts or heat damage before proceeding.
How to Insulate the Cut End Correctly
8. Fit the matched comb busbar end cap
The exposed cut face is normally protected with the end cap specified for that busbar system. Match the cap to the product family, conductor profile, pole configuration and sleeve dimensions.
Push the cap into its documented position without forcing or modifying it. A correctly fitted cap should:
- fully enclose the cut conductor face;
- seat against the insulated busbar body as designed;
- remain secure without splitting or bulging;
- avoid interference with the adjacent breaker, enclosure or barrier; and
- preserve the completed assembly’s required contact protection and insulation arrangement.
Some busbar systems require end caps at both ends; others supply one factory-finished end and require protection only where the bar was cut. Follow the product drawing rather than applying one rule to every model.
Why electrical tape is not a substitute
Electrical tape may shift, loosen, tear on a burr or produce an uncontrolled thickness. It does not establish that creepage, clearance, retention or contact protection has been restored. Generic heat-shrink tubing has similar limitations and may introduce heat during installation.
Use tape, heat shrink, moulding compound or another alternative only when the busbar manufacturer or verified assembly procedure explicitly defines that method. “No copper is visible” is not, by itself, proof of an acceptable insulation system.
9. Protect unused live teeth
An end cap covers the cut face; it does not cover unused contacts along the bar. If a live tooth remains outside a breaker terminal, use the specified tooth cover, protection cap or barrier—or revise the cut length—according to the system instructions.
Do not describe the completed row as finger-safe merely because the main conductor has a plastic sleeve. Teeth, feeder terminals, unused contacts and cut ends may remain accessible until the correct devices, covers, barriers and enclosure are installed.
Reinstalling and Verifying the Comb Busbar
10. Refit the busbar without forcing the teeth
Align every contact with its intended terminal before applying pressure. The bar should seat evenly across the row. Do not use terminal screws to pull a tilted busbar into alignment.
Vérifier que :
- every pin or fork enters the compatible terminal position;
- the insulation does not hold a contact outside the clamp;
- no tooth is bent, offset or only partly captured;
- the end cap does not prevent full insertion;
- the phase and neutral sequence matches the schematic; and
- unused live positions are protected.
Tighten each terminal using the device manufacturer’s stated method and torque. There is no safe universal torque value for every MCB and comb busbar combination.
11. Complete the assembly verification
Before energization, apply the inspection and test procedure required for the completed distribution board. As applicable, verify:
- correct device and busbar part numbers;
- continuity and phase sequence;
- insulation resistance or dielectric verification under the approved assembly procedure;
- specified clearances to the enclosure, neutral bar, protective-earth bar and other conductive parts;
- correct terminal tightening and full contact capture;
- absence of copper swarf, loose hardware and damaged insulation;
- installation of end caps, tooth covers and barriers; and
- correct enclosure covers and access protection.
Do not treat a successful continuity check as proof that the connection has sufficient contact area or thermal performance. A partially captured tooth can conduct during a low-current test and still overheat in service.
Correct vs Incorrect End Preparation
| Inspection point | Acceptable condition | Reject or correct |
|---|---|---|
| Cut permission | Exact product documentation allows shortening | Model is fixed-length, prohibited from cutting or undocumented |
| Cut face | Square, smooth and free of loose burrs | Crushed, angled, torn or sharply burred |
| Isolation | Intact along the bar with no longitudinal crack | Split, scorched, shaved back without instruction or loose |
| Teeth | Straight, clean and correctly spaced | Bent, twisted, filed or partly cut |
| End cap | Correct part, fully seated and mechanically stable | Generic cap, poor fit, cracked cap or exposed cut face |
| Unused contacts | Protected by specified covers or removed by approved cut length | Accessible live tooth left uncovered |
| Device seating | Every tooth fully enters its intended compatible terminal | Tooth is tilted, outside the cage or clamped only at an edge |
| Cleanliness | No conductive particles remain | Copper swarf present in terminals or enclosure |
Common Comb Busbar Cutting Mistakes
Cutting before checking the catalog number
Visual similarity is not evidence that two busbars share the same modification rules. Confirm the exact part first, particularly where product approval or assembly documentation must be maintained.
Measuring from enclosure width instead of contact positions
This can leave an extra live tooth, remove a required contact or shift the intended phase sequence. Measure from the final device row and approved drawing.
Cutting the busbar while it is installed
This can send conductive filings into protective devices, damage terminals and expose the worker to electrical and mechanical hazards. Remove the de-energized part before cutting.
Using cutters that crush the conductor
A fast cut is not necessarily a controlled cut. Deformation can prevent the end cap from seating and may crack the insulation beyond the visible cut face.
Fitting an end cap without deburring
A sharp copper edge can cut the cap or hold it away from its designed position. Deburr and clean first.
Leaving an unused tooth exposed
The cut end may be protected while another contact remains live and accessible. End caps and tooth covers perform different functions.
Mixing busbar and breaker families after cutting
Shortening does not make an incompatible busbar compatible. Pin or fork form, pitch, thickness, insertion depth and terminal construction still have to match.
Normes et limites du fabricant
CEI 61439-3:2024 defines requirements for distribution boards intended to be operated by ordinary persons within its stated scope. It applies to the completed assembly; it is not a universal cutting instruction for every MCB comb busbar.
The busbar and device manufacturers define whether a particular product can be shortened, which accessories are required and how the modified part may be used. The panel builder must also preserve the verified assembly arrangement, applicable wiring rules and local occupational-safety requirements.
Do not transfer a cutting method, end-cap part number or approval statement from one busbar family to another. Even products from the same manufacturer may use different conductor sections, sleeve profiles and end-protection systems.
Final Acceptance Checklist
Do not release the modified busbar for installation until every applicable item is confirmed:
- □ Exact busbar model verified as cuttable
- □ Breaker series, pin/fork interface and pitch confirmed
- □ Pole and phase sequence checked against the schematic
- □ Cut made at the approved position with the approved tool
- □ Cut face square, smooth and deburred
- □ Teeth and insulation undamaged
- □ All conductive debris removed
- □ Correct end cap fully seated
- □ Unused live teeth protected
- □ Busbar fully seated in every compatible terminal
- □ Terminal tightening completed to device instructions
- □ Completed-board inspection and required testing passed
Foire Aux Questions
Can every MCB comb busbar be cut to length?
No. Some products are cuttable, while others are supplied only in fixed approved lengths. Confirm the exact catalog number and installation instructions. Do not infer cutting permission from appearance or from another product in the same range.
What is the best tool for cutting a comb busbar?
Use the tool specified for the exact product. Some manufacturer instructions call for a saw followed by filing; other systems may use a dedicated cutter. The tool must make a controlled cut without crushing the conductor, cracking the insulation or bending adjacent teeth.
Can I cut a comb busbar with side cutters?
Not unless the manufacturer specifically authorizes that method. Side cutters and bolt cutters commonly deform the conductor and insulation rather than producing the square, smooth end needed for a matched cap.
Does a cut comb busbar always need an end cap?
The exposed cut end normally requires the matching end cap or the specific protection defined by the product system. Follow the exact instructions. A factory-finished end may already be protected, while a newly cut face is not.
Can heat-shrink tubing replace a comb busbar end cap?
Only if the manufacturer or verified assembly procedure explicitly permits it. Generic heat shrink does not automatically reproduce the cap’s fit, retention, clearance or contact-protection function.
Where should a three-phase comb busbar be cut?
Cut it only at the position allowed by the product drawing and the actual device layout. Confirm the repeating phase sequence and every connected pole before marking. There is no universal “cut after any third tooth” rule that fits all MCB, RCCB and RCBO arrangements.
Can I cut the busbar without removing it from the breakers?
No. Isolate and verify the assembly is de-energized, then remove the busbar. Cutting an installed bar risks conductive debris entering devices, mechanical damage and unsafe exposure.
How should unused comb busbar teeth be insulated?
Use the tooth covers or protection caps specified for that busbar system, or shorten the bar using an approved method. An end cap protects the cut face but does not automatically protect unused teeth along the bar.
Can VIOX comb busbars be cut?
Cutting permission depends on the exact VIOX model, drawing and ordered configuration. Before modification, confirm the busbar series, pole arrangement, contact geometry, length and required end-protection accessories with VIOX or the supplied product documentation.
Recommandation finale
A correctly shortened comb busbar is not simply a long bar made shorter. It is a modified distribution component whose contact pattern, insulation, end protection and compatibility must remain controlled.
Utilisez la séquence suivante : confirm it is cuttable, map the device row, cut square, deburr and clean, fit the matched end cap, protect unused teeth, then verify the completed assembly. If the exact cutting rule or accessory cannot be confirmed, use the correct factory length or request a matched configuration instead of improvising.
For product matching, review the VIOX pin and fork MCB comb busbar range and submit the breaker series, terminal type, pole layout, pitch, required length, phase arrangement and target-market documentation.
Sources
- Gamme de peignes de raccordement pour disjoncteurs modulaires VIOX.
- VIOX MCB busbar and comb busbar selection guide.
- Schneider Electric — Can Multi 9 C60BP comb busbars be cut to any desired length?.
- Schneider Electric — Easy9 Consumer Unit instruction sheet NVE10739.
- ABB — Busbars PS…CB and accessories.
- IEC 61439-3:2024 — Tableaux de répartition destinés à être utilisés par des personnes ordinaires.