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Busbar Testing: Methods, Standards and What You Receive
Every busbar leaving our plant is checked against the drawing for dimensions, plating and insulation. Beyond that, four tests decide whether an insulated busbar survives its service life: salt spray, dielectric strength, coating adhesion and temperature rise. This page sets out how each one is run and what you receive with the parts.
What comes with a first article
A first article report accompanies the first production batch of any new part. It lists the measured dimensions against the drawing, the plating thickness, the insulation thickness and the results of whichever electrical and environmental tests your specification calls for. Each test carries a report number. Full reports are available on request under NDA.
For a program under automotive quality requirements the same data flows into the part approval package. What that means for approval and change control is set out on the IATF 16949 busbar supplier page.
Dimensional and visual inspection
This is the check that catches the most problems and the least glamorous one. Hole position, pad flatness, overall length, bend angle and mask line position are measured against the drawing. A busbar that meets every electrical requirement but misses a hole pattern by half a millimeter is scrap at your assembly line, so the dimensional report comes first.
What gets measured is set by the drawing rather than by a standard checklist. Dimensions the customer has marked as controlled are measured on every part; the rest are checked at a frequency agreed for the program. Mark the critical dimensions on the drawing and they will be the ones reported.
Salt spray
Corrosion resistance is run as a neutral salt spray test to ISO 9227 salt spray test method, a 5% sodium chloride mist at 35 °C. The Chinese standard GB/T 10125 adopts the same NSS conditions, so a report issued under either one is directly comparable, and the same holds for ASTM B117 and JIS Z 2371. Automotive programs commonly ask for 480 to 720 hours with no blistering and no coating loss.
Coating thickness drives the result more than any other variable, which is why the salt spray report is read alongside the thickness measurement rather than on its own. Thickness ranges for each process are on the the PVC dipping process page and the epoxy powder coating process pages.
Chamber time is the constraint. A 480 hour test occupies 20 days and a 720 hour test 30, so the salt spray requirement belongs in the specification before the first article rather than after it. Where a program needs the report to come from an accredited third-party laboratory, say so with the enquiry and the test is placed accordingly.
Dielectric strength and withstand voltage
Two different numbers get confused here, so it is worth separating them. Dielectric strength in kV per millimeter is a property of the cured coating material, measured on a flat specimen to IEC 60243-1 or its identical Chinese equivalent GB/T 1408.1. Withstand voltage is a pass or fail test on the finished part: a set voltage applied for a set time, usually 60 seconds, between the conductor and a grounded surface.
The finished part always withstands less than the material figure suggests, because field concentrates at edges and at the thinnest point of the film rather than at the average thickness. Specify the withstand voltage your application needs and we will confirm the coating build that reaches it with margin at the thinnest point.
The test voltage and hold time come from your specification, not from ours. Tell us the value and whether it is applied to every part or to a sample, because a 100% withstand test on a high-volume part changes the line layout and belongs in the quotation rather than in a change request later.
Coating adhesion
Adhesion is graded by the cross-cut test in ISO 2409, adopted identically as GB/T 9286. A lattice is cut through the coating down to the copper, tape is applied and removed, and the proportion of coating detached puts the sample in a class from 0 to 5. The result is a class, not a percentage, and 0 is best. Industrial coating work is normally accepted at Class 0 or 1.
Cut spacing follows coating thickness: 1 mm below 60 µm, 2 mm from 60 to 120 µm and 3 mm above that. A class reported without its cut spacing cannot be compared against anything, so both go in the report.
Temperature rise
A busbar is sized by the temperature it reaches, not by a current figure on its own. The test applies a continuous current and measures the rise above ambient at defined points, with the part in the installation condition it will actually see. IEC 61439-1 sets the ceiling for accessible busbars at a 70 K rise over a 35 °C ambient.
Inside a battery pack the practical limit is usually lower than the standard allows, because the insulation gives out before the copper does. PVC compounds are commonly rated to around 105 °C and heat-shrink tubing to 125 °C. A temperature rise figure quoted without the ambient and the enclosure condition tells you almost nothing.
Three things have to be fixed before a temperature rise result means anything: the current, the ambient and whether the part sits in free air or in the enclosure it will actually occupy. Give us those and the measurement points, and the result is comparable against your own bench data. Without them, any number quoted is only true of the conditions it happened to be measured in.
Plating and material checks
Plating thickness is measured before insulation, because it cannot be checked afterwards without destroying the part. Copper grade is controlled at incoming inspection: stock is T2 or C11000 ETP copper at 100% IACS or better, and the mill certificate is retained with the batch record. Where a customer specifies a particular alloy or conductivity, that requirement flows into incoming inspection rather than being caught at the end.
Which standard applies to which test
| Test | International | Chinese equivalent | Relationship |
|---|---|---|---|
| Neutral salt spray | ISO 9227 | GB/T 10125 | Equivalent adoption |
| Electric strength | IEC 60243-1 | GB/T 1408.1 | Corresponding |
| Cross-cut adhesion | ISO 2409 | GB/T 9286 | Identical adoption |
| Temperature rise | IEC 61439-1 | GB/T 7251.1 | Corresponding |
| Copper busbar stock | EN 13601 | GB/T 5585.1 | Parallel national standards |
Reporting under the Chinese standard rather than the international one is not a downgrade where the test conditions are the same, and for neutral salt spray they are. Where a customer requires the report to name a specific standard, the test is run and reported under that standard rather than relabeled afterwards.
Safety standards around the part
A busbar is not certified on its own. It is qualified as part of a system, and the requirements that drive clearance, creepage and withstand numbers come from the system standards. ISO 6469-1 electrical safety covers the rechargeable energy storage system in road vehicles. IEC 62619 safety requirements covers industrial secondary cells and batteries. Stationary storage programs increasingly ask for evidence against the UL 9540A test method for thermal runaway propagation.
Frequently asked questions
- Can I see the actual test reports?
- Yes, under NDA. Each test carries a report number, and that number appears on the first article report, so you can request a specific document rather than a generic certificate.
- Can the report come from an accredited third-party laboratory?
- Yes, where your program requires it. Say so with the enquiry rather than after the first article, because third-party scheduling adds lead time and the cost belongs in the quotation.
- Is every part tested, or a sample?
- Dimensional and visual inspection covers every part. Destructive and environmental tests run on samples. The sampling plan is agreed per program, because a prototype batch and a series-production part do not warrant the same frequency.
- What is the difference between dielectric strength and withstand voltage?
- Dielectric strength in kV per millimeter is a material property measured on a flat specimen. Withstand voltage is a pass or fail test on the finished part at a set voltage for a set time. Specify the second one. The first is a design input, not an acceptance criterion.
- How long does salt spray testing take?
- As long as the specification calls for. A 480 hour test occupies 20 days of chamber time and a 720 hour test 30 days. This is why the salt spray requirement should be agreed before the first article rather than after it.
- Can you test to our own internal specification?
- Yes. Send the specification with the drawing. Where it calls for equipment we do not hold, the test goes to a third-party lab and the report comes back under that lab’s name.
Request a quote
Send the drawing and the test requirements together. Quoting a part without knowing the withstand voltage and the salt spray hours means quoting the wrong part. Start an RFQ.