To measure MCB busbar pitch, identify the center of the first and last selected contact, measure the center-to-center span, and divide that span by the number of intervals. Five contact centers contain four intervals, not five. Measure across several contacts, record any change in the sequence, and confirm the result against the exact device or busbar drawing. Nominal device width alone is not proof of busbar tooth spacing.
> Pitch formula: `pitch = center-to-center span ÷ number of intervals`
This calculation documents one part of compatibility. It does not prove the correct pin or fork interface, contact dimensions, vertical alignment, phase sequence, electrical rating, or complete-assembly suitability.
What busbar pitch actually measures
For an MCB or other modular device, busbar pitch is the horizontal center-to-center distance between corresponding contacts in a repeated connection pattern. The reference points must be consistent: pin center to pin center, fork centerline to fork centerline, or the intended terminal-clamp centerline to the next equivalent centerline.
Four terms keep the measurement unambiguous:
| Term | Meaning | Common mistake |
|---|---|---|
| Contact center | The geometric centerline of the busbar tooth or intended terminal engagement position | Measuring from one outside edge to another |
| Interval | One center-to-center step between adjacent selected contacts | Counting contacts instead of spaces |
| Span | Distance from the first selected center to the last selected center | Using the overall device-row width |
| Pitch | Span divided by interval count for a uniform repeated pattern | Treating one catalogued module width as universal |
If you identify contact centers at positions 1, 2, 3, 4, and 5, the span from position 1 to position 5 covers four intervals. That interval count is the denominator in the formula.
Why measure several contact intervals
A single adjacent-center reading concentrates every marking, viewing, and caliper-placement error into one short distance. A longer span distributes the reading across several intervals and also reveals whether a small pitch difference would accumulate along the row.
Use two calculations for a uniform candidate:
```text measured pitch = first-to-last center span ÷ number of intervals accumulated offset = (candidate pitch − required pitch) × number of intervals ```
The second result is a diagnostic value, not a universal acceptance rule. It tells you how far two nominal patterns would diverge over the measured interval count. The exact pass/fail limit must come from the controlled product drawing, device manufacturer, approved sample, and project verification process.
For example, a difference that looks small at one tooth becomes easier to detect across eight or twelve intervals. Do not use that observation to force a near-match into place. If the product references disagree—such as 17.8 mm versus 18 mm—stop and verify the exact system.
Identify the pattern before calculating one number
Not every modular-device row has one uniform pitch. Classify the connection pattern first.
1. Uniform repeated pitch
Every equivalent contact advances by the same horizontal step. A single pitch value plus the contact count can describe the repeated pattern, provided vertical alignment and terminal geometry also remain constant.
Record it as, for example: `P = [measured value] mm, positions 1–12, 11 intervals`.
2. Repeating multi-step pattern
Some phase/neutral or compact-device arrangements repeat more than one horizontal distance. A KASEEY DPN-LE product drawing, for example, uses a 9 mm primary device distance and a 27 mm secondary distance within its named pattern. That is not one 18 mm-pitch row and should not be reduced to an average.
Record the complete sequence, such as `9 / 27 / 9 / 27 mm`, together with which conductor or contact position each step serves.
3. Interrupted or mixed pattern
An auxiliary, spacer, RCCB, RCBO, isolator, surge protective device, or different device family may break the repetition. Mark the interruption as a boundary. Then measure each internally uniform group separately and document how the transition will be handled.
The comb busbar versus jumper-wire guide explains when a row should use one comb, separate comb groups, jumper conductors, or another approved distribution method.
9 mm, 17.8 mm, and 18 mm are product-specific examples
These numbers appear in modular-device systems, but they are not a universal substitution table.
| Published example | What the source establishes | What it does not establish |
|---|---|---|
| KASEEY DPN pin busbar: 9 mm device distance | A named compact DPN product series uses a 9 mm contact pattern | Every 9 mm product fits every half-module device |
| KASEEY P-2L-D pin busbar: 17.8 mm device distance | A named two-phase closed pin busbar series uses 17.8 mm | 17.8 mm can be rounded to 18 mm for any breaker row |
| Siemens modular system: 1 MW = 18 mm | A named Siemens miniature-circuit-breaker system defines one modular width as 18 mm | All products described as one module share the same terminal centerline and busbar interface |
| Schneider Acti9 3P+N balanced comb: 9 mm pitch | A named comb busbar has a published 9 mm pitch and its own module arrangement | Its sequence or geometry transfers to another device family |
The correct interpretation is exact and narrow: the product drawing defines the candidate busbar pattern, and the exact device documentation or approved sample defines the required contact positions. Similar numbers are a reason to inspect more carefully, not permission to treat the products as interchangeable.
For the wider selection task—including terminal type, poles, cross-section, teeth, length, feed, and accessories—use How to Select an MCB Busbar. If the uncertainty is specifically pin versus fork, use the separate pin-type versus fork-type busbar comparison.
Step-by-step MCB busbar pitch measurement
Use a controlled device drawing whenever it provides the required terminal-center dimensions. If a physical check is needed, use a de-energized loose sample prepared for inspection. Do not take measurements around live exposed terminals.
Step 1: freeze the exact device row
Record manufacturer, full model, pole arrangement, accessories, spacers, and left-to-right order. Do not substitute a similar-looking breaker during measurement.
Step 2: choose one connection-side reference
State whether you are mapping the line or load side and where the busbar contact is intended to engage. Use the device drawing to identify the correct clamp path. A terminal opening edge is not necessarily the contact center.
Step 3: mark the contact centers
Create a numbered center for every intended busbar position. For a fork contact, use the fork centerline—not one tine. For a pin, use the pin centerline. If the terminal center shifts vertically or horizontally, record the offset instead of pretending the pattern is uniform.
Step 4: select a multi-contact span
Use as many clear, equivalent positions as the row allows. Measure from the first selected center to the last selected center, then count the intervals between them.
Step 5: calculate and cross-check
Divide the span by the interval count. Then calculate at least one shorter sub-span inside the group. Consistent sub-spans support the repeated-pattern reading; inconsistent results can indicate a marking error, mixed pattern, or interrupted lineup.
Step 6: record the geometry that pitch cannot describe
Add pin or fork form, contact width or diameter, insertion length, vertical centerline, insulation and end-treatment requirements, conductor sequence, and any unused position. Equal pitch alone does not prove fit.
Step 7: compare controlled sources
Compare the measured record with the exact device drawing, candidate busbar drawing, and approved sample where required. If the sources conflict, retain the conflict in the review record and stop the release instead of rounding a value.
Worked example: five contact centers
Assume a de-energized sample row has five clearly marked, equivalent contact centers. The measured span from center 1 to center 5 is 71.2 mm.
```text contact centers = 5 intervals = 5 − 1 = 4 measured span = 71.2 mm calculated pitch = 71.2 ÷ 4 = 17.8 mm ```
Now compare a hypothetical 18.0 mm candidate over the same four intervals:
```text accumulated offset = (18.0 − 17.8) × 4 = 0.8 mm ```
This arithmetic does not declare the candidate acceptable or unacceptable. It shows that the two patterns diverge by 0.8 mm from the first to the fifth contact. The release decision still requires the named device and busbar documentation, permitted dimensional limits, terminal geometry, and sample or assembly verification.
When one pitch value is not enough
Do not issue an RFQ with only `18 mm pitch` or `9 mm pitch` when the row includes any of the following:
alternating phase and neutral positions;
a compact DPN or distributed-neutral sequence;
different device widths or terminal centerlines;
auxiliaries or spacers without a normal main contact;
a gap between two busbar groups;
mixed pin, fork, blade, or dedicated terminal interfaces;
vertical offsets that change engagement depth;
different conductor sequences across the row.
In these cases, supply a position map. Label each contact by position and conductor, state every horizontal step, and mark each interruption. A drawing or annotated photograph is more reliable than an averaged pitch value.
Pitch measurement record
Copy this table into the drawing review, sample report, or RFQ package.
| Field | What to record | Example format |
|---|---|---|
| Device row | Manufacturer, exact models, poles, accessories, order | Model A × 6 + auxiliary + Model B × 4 |
| Connection side | Line/load side and intended clamp path | Line side, lower terminal, documented busbar path |
| Contact references | Numbered center positions and conductor labels | 1=L1, 2=L2, 3=L3, 4=N |
| Measured span | First center, last center, distance and tool/resolution | C1–C5 = 71.2 mm |
| Interval count | Number of center-to-center spaces | 4 intervals |
| Calculated pitch | Span divided by intervals | 17.8 mm |
| Pattern | Uniform, repeating multi-step, or interrupted | Uniform C1–C5; interruption after C5 |
| Other geometry | Contact form, dimensions, vertical offsets, engagement | Pin Ø4 mm; verify length on drawing |
| Candidate reference | Exact busbar model and drawing revision | Supplier drawing number/revision |
| Evidence source | Device drawing, controlled sample, test or approval record | Manufacturer drawing + approved sample |
| Open conflicts | Any mismatch or missing limit | Candidate says 18 mm; device record says 17.8 mm |
| Release status | Approved, revise, sample required, or stop | Sample required |
Send the pattern, not only the nominal pitch
A useful MCB busbar pitch record contains the exact device row, contact-center map, first-to-last span, interval count, calculated pitch or full sequence, terminal form, vertical offsets, conductor order, candidate drawing, and unresolved differences. That package lets engineering and sourcing teams review the same geometry.
Browse the KASEEY busbar range for product-specific dimensional data. For a nonstandard pattern, review the modular-device busbar solution or custom busbar OEM service. To request compatibility review, send the completed pitch record, exact device list, drawings or de-energized samples, electrical requirements, quantity, and destination market through the KASEEY contact page.
