The most-quoted number on the Molex PicoBlade is 2.5A.

It is also not a rating, and the difference costs people design margin. Here is the full picture — what "MX1.25" actually refers to, why its current specification is three numbers rather than one, and what to check before you cross-reference it.

I work on connector and harness programmes at KONNRA, which builds a documented cross-reference to this system (the KR1250 for wire-to-board, KR1251 for wire-to-wire).

What "Molex MX1.25" actually means

Molex does not sell a product called "MX1.25." The string is trade shorthand built from the 1.25mm pitch, and it maps to the Molex PicoBlade 1.25mm connector system.

• 1.25mm pitch, single row, 2 to 15 circuits
• Wire-to-board and wire-to-wire — both, in the same family
• Two-point contact design — each mating pair touches in two places
• Friction lock — retention by friction, no positive latch
• 125V AC (RMS)/DC
• Rated current: 1.0A at AWG #26, #28 and #30 · 0.8A at AWG #32
• Reference derating published separately — up to 2.5A at 2 circuits
• Applicable wire: AWG #26 to #32; insulation up to φ1.0mm (terminal 50058802*) or φ1.04mm (50079802*)
• Contact resistance: 20mΩ max initially, 5mΩ max for the crimped portion, 40mΩ max after environmental exposure
• Insulation resistance: 100MΩ min · Dielectric strength: 250V AC (RMS), 1 minute
• −40°C to +105°C, including terminal temperature rise
• 30 mating cycles with gold plating
• Plating options: gold flash · 0.38µm min gold · tin
• Molex series numbers: 51021 receptacle housing · 53048 right-angle plug assembly
• Standards: UL File E29179
• KONNRA equivalents: KR1250 (wire-to-board) · KR1251 (wire-to-wire)

The current rating is three numbers, not one

This is the parameter most often quoted wrong, because Molex publishes it at three levels and only one of them is the rating.

Level 1 — the rated current, by wire size:

• AWG #26 → 1.0A
• AWG #28 → 1.0A
• AWG #30 → 1.0A
• AWG #32 → 0.8A

Level 2 — the reference derating table, by gauge and circuit count, with columns at 2, 8 and 15 circuits:

• AWG #26 → 2.5A at 2 circuits · 1.5A at 8 · 1.0A at 15
• AWG #28 → 2.0A · 1.5A · 1.0A
• AWG #30 → 1.5A · 1.0A · 1.0A
• AWG #32 → 1.5A · 1.0A · 0.8A

Level 3 — the sum rule. Molex adds: "Do not allow the sum of the current used on several circuits to exceed the maximum allowable current." The per-circuit figure is not the whole answer.

Why the 2.5A is the most dangerous number on this connector. It is real, and it is reference data, not a rating. Molex states the conditions explicitly: the values are for reference only, the derating is based on not exceeding a 30°C temperature rise, the rise is measured in the barrel area of the crimp terminal, the data is for all circuits powered, and — the one that matters most — PCB trace design can greatly affect temperature rise results.

So if your design needs 2.5A through two PicoBlade circuits, the number to work from is your own temperature-rise test on your own board, not a datasheet row. Treating 2.5A as a rating is how designs end up relying on margin that was never specified.

The counterintuitive part: the bigger pitch carries less current

The PicoBlade is 1.25mm at 1.0A. Molex's Pico-EZmate is 1.20mm at 1.5A — a smaller pitch with a higher current rating. JST's ACH at 1.2mm reaches 2A on 1–3 circuits. And Molex's own Pico-EZmate Plus does 2.8A at 1.00mm.

Do not assume the bigger connector is the stronger one. On this family it is not, and the two systems do not mate — 1.25mm is not 1.20mm, and over a 15-circuit connector the difference compounds across the contact field. KONNRA cross-references the Pico-EZmate as KR1200 and the PicoBlade as KR1250/KR1251.

So what is the PicoBlade's case? Not current. It is three things:

• The two-point contact design. Molex's stated reason is direct: rugged applications "can be subject to shock, vibration or rough handling that can dislodge the terminals and cause signal interference." Two contact points per pair means a single disturbed point does not open the circuit.
• The 125V rating. At the same 1.25mm pitch, JST's GH series is rated 50V. That is a material difference if your circuit runs above 50V — and if it does, GH is not an option at any current.
• One family for both connection types. Wire-to-board and wire-to-wire on the same contact system, so both ends of a run can use it.

The friction lock is not your cable retention

Retention here is by friction, with no latch to release. Molex's own withdrawal force table shows how modest that is:

• 2 circuits — 2.8N minimum at first mating, 1.8N by the 30th cycle
• 5 circuits — 3.8N, falling to 2.8N
• 8 circuits — 5.2N, falling to 4.3N
• 15 circuits — 7.3N, falling to 6.3N

A 2-circuit connector holds with under 3 newtons, and under 2 newtons after 30 cycles. The friction lock keeps the pair mated; it does not carry your cable load. Molex's design guidance says the same thing from the other direction: tie the cable at least 50mm from the connector edge, with the force applied evenly across all wires, so the terminals can float freely in their pockets.

Four crimp terminals — and at AWG #28 the plating decides

Molex splits the terminal across four part numbers: two wire ranges, each in two plating thicknesses.

• 500798020 — AWG #26–28, gold flash
• 500798025 — AWG #26–28, 0.38µm min gold
• 500588020 — AWG #28–32, gold flash
• 500588025 — AWG #28–32, 0.38µm min gold

The two wire ranges overlap at AWG #28, so at that gauge you have four options and two independent questions — which gauge family, and which finish. Molex makes the distinction explicit: flash versus 0.38µm minimum. That is exactly what a BOM line saying "gold plated" fails to record.

Insulation diameter differs by terminal as well: the 50058802* family allows φ1.0mm maximum, the 50079802* family φ1.04mm.

Two gaps on the KONNRA side to be aware of: the published KR1250 documents one terminal with a stated range of AWG #28 to #32, and it documents "Gold flash / Tin over Nickel" without a thickness figure — so the 0.38µm gold option is not documented, and neither is the AWG #26 path.

Circuit counts and the AWG #26 gap

Molex states the PicoBlade is "available in 2 to 15 circuits," and both the derating and the force tables run to 15. KONNRA documents the KR1250 as 2 to 16 positions — one beyond the original range.

The wire-range gap matters more than the circuit gap, because AWG #26 is where this family's capability is concentrated: it carries the highest derated current in Molex's table (2.5A at 2 circuits) and the highest crimp pull-out force (19.6N minimum, against 9.8N at AWG #28). KONNRA's stated KR1250 wire range is AWG #28 to #32, which does not cover #26. If your harness uses it, say so explicitly.

Cross-referencing to the KONNRA KR1250 — the honest gaps

Where the documents agree is worth stating, because on a cross-reference it is not a given: the pitch, the single-row configuration, the 125V rating, the 20mΩ contact resistance, the 100MΩ insulation resistance, the −40°C to +105°C range, the two-point contact design, and the friction lock. On this series the agreement is broad.

Where they differ:

• Rated current at AWG #32 — 0.8A versus a flat 1A. At AWG #26, #28 and #30 the figures match at 1.0A, so this is specifically an AWG #32 issue, and the published KR1250 figure is 25% optimistic at that gauge.
• The wire range does not reach AWG #26 — covered above, and it is the gap most likely to matter.
• The insulation window is narrower on the KONNRA side. Molex allows up to φ1.0mm or φ1.04mm depending on terminal; KONNRA documents 0.4 to 0.8mm. A wire with 0.9mm insulation passes Molex's spec and falls outside KONNRA's stated maximum. Check both ends against your cable.
• Dielectric withstanding voltage differs by a factor of two — in KONNRA's favour. Molex specifies 250V AC (RMS) for one minute; KONNRA documents 500V AC / minute. A higher figure on the replacement is not automatically a problem, but it is a different test claim — confirm what is tested and between which points. The rated voltage, 125V, is the same on both sides.
• Mating durability is published by Molex and not by KONNRA. Molex specifies 30 cycles with gold plating. KONNRA publishes no cycle count for the KR1250.
• Plating thickness is specified by Molex and not by KONNRA. Molex offers three finishes and the thickness is part of the terminal part number. KONNRA states "Gold flash / Tin over Nickel" with no thickness.
• The KONNRA page contradicts itself on plating. Its specification table says "Gold Flash/Tin over Nickel", while its advantages text says "the contact area is tin-plated." Those describe different finishes on the same mating interface. On a two-point contact interface the finish determines long-term contact resistance stability, so it is worth resolving before quoting.
• Circuit counts — 2 to 15 versus 2 to 16. One position beyond the original range.
• Wire-to-board versus wire-to-wire. KONNRA's KR1250 Overview says the series supports both, but its own 1.25mm listing categorises KR1250 as wire-to-board, and the wire-to-wire part is KR1251. If your design is inline, the cross-reference you want is KR1251.
• Applicable wire construction. Molex specifies, in principle, tin-plated copper stranded wire, and says other constructions require consultation and evaluation. KONNRA does not state a construction. Anything else — silver-plated, solid core, high-flex — should be raised before qualification.

Why 20mΩ is not the whole contact-resistance story

Molex specifies 20mΩ max initially, and 40mΩ max after environmental exposure — vibration, mechanical shock, temperature cycling, heat, cold, humidity, salt spray, and SO₂ and NH₃ gas. All of those tests are specified with conditions in the datasheet.

If a specification quotes a single contact-resistance figure without saying which condition it applies to, it is incomplete. The two figures are a factor of two apart, and the difference is the one that shows up after the product has been in the field.

What to send for a cross-reference check

1. The original part number, if you have it — a housing such as 51021**00, a terminal such as 500798025, or a plug assembly such as 53048**60
2. Circuit count — the Molex range is 2 to 15
3. Wire gauge, and specifically whether it is AWG #26 — inside Molex's range and outside the published KR1250 range
4. Insulation outside diameter, not just the gauge — Molex allows up to φ1.0mm or φ1.04mm depending on terminal; KONNRA documents 0.4–0.8mm
5. Plating finish required — flash or a specified gold thickness; 0.38µm minimum is a distinct Molex option
6. Mounting and orientation — through-hole or SMT, straight or right-angle
7. Wire-to-board or wire-to-wire — KR1250 for wire-to-board, KR1251 for wire-to-wire
8. Your load current, so the AWG #32 0.8A question and the derating position are settled rather than assumed
9. Application and annual volume
10. A drawing or photo, if the part number is unreadable

With those, four things get confirmed against Molex's own documentation: the terminal that matches your wire gauge and insulation diameter, the gold thickness you need, the wafer orientation and mounting type, and whether your design needs the wire-to-board or wire-to-wire variant.

Quick identification check. Measure the pitch — 1.25mm points at Molex PicoBlade, Molex PanelMate, Hirose DF13/DF14 or JST GH; 1.20mm at Pico-EZmate or JST ACH; 1.00mm at Pico-Clasp or JST SH. Then count positions: the PicoBlade is documented from 2 to 15, so more than 15 is not a standard PicoBlade. Look for the two-point contact geometry and the friction lock. Part numbers: 51021 is the receptacle housing, 53048 the right-angle plug assembly, and a 5005 / 5007 prefix indicates a crimp terminal.

Full technical write-up: Molex MX1.25 Connector Complete Guide

Disclosure: I work with KONNRA, which manufactures the KR1250 and KR1251 cross-references. The Molex PicoBlade figures above are taken from Molex's published Product Specification 510211000-PS; the KONNRA figures are from our published KR1250 documentation. Where the two disagree — or where one source contradicts itself — I have flagged the difference rather than averaged it.

https://konnra.com/molex-mx1-25-connector-complete-guide/
Dongguan Konnra Electronics Co., Ltd