IEC 61439 in Plain Terms: What a Type-Tested LV Assembly Means and What Your Panel Builder Must Prove

Under IEC 61439, a “type-tested” low voltage panel is one whose design has passed design verification against thirteen characteristics, and whose every individual unit has then passed routine verification before dispatch. The standard no longer uses the old labels TTA and PTTA. It asks two questions instead: has this design been proven, by test, by comparison with a tested reference design, or by assessment, and has this particular panel been checked against that proven design? A panel builder who cannot answer both, for the exact rating on your order, has not shown you an IEC 61439 assembly.

TL;DR

• IEC 61439 replaced “type-tested” and “partially type-tested” with two proofs: design verification, done once per design, and routine verification, done on every panel.

• For an industrial PCC or MCC, the governing documents are IEC 61439-1:2020 and IEC 61439-2:2020, adopted in India as IS/IEC 61439.

• The standard splits responsibility between the original manufacturer, who designs and verifies the system, and the assembly manufacturer, who builds your panel and puts its name on the nameplate.

• Temperature rise and short-circuit withstand are the two verifications a cheaper build most easily undermines. Short-circuit withstand cannot be proven by calculation alone.

• A panel builder who modifies a verified system beyond the original manufacturer’s instructions becomes the original manufacturer for that modification, and owns its verification.

• Ask for evidence tied to your rating: rated current, rated short-time withstand current, form of separation and IP, not a generic certificate.

What does “type-tested” actually mean under IEC 61439?

Under IEC 61439, “type-tested” means a panel design has been through design verification, and the panel you receive has been through routine verification against that design. Eaton’s EN 61439 white paper records that the terms TTA and PTTA, used under the older EN 60439 series, “are no longer included” in the EN 61439 series. The replacement is a clearer split between proving a design and checking a product.

Design verification is defined in IEC 61439-1, as quoted in Siemens’ guide to documentation of verifications, as “verification on specimens of a switchgear and controlgear assembly or on parts thereof to show that the design fulfills the requirements of the applicable standard.” Routine verification is the check “to which every switchgear and controlgear assembly is subjected during and/or after manufacture.”

The practical difference for a buyer is that the question becomes precise: which verified design is this panel built to, and where is the routine verification record for this serial number?

Which parts of IEC 61439 apply to an industrial PCC or MCC?

An industrial power control centre (PCC) or motor control centre (MCC) is governed by two parts read together. IEC 61439-1:2020, the third edition published on 5 May 2020, lays down the general definitions, service conditions, construction requirements, technical characteristics and verification requirements. IEC 61439-2:2020, published on 22 July 2020, adds the specific requirements for power switchgear and controlgear assemblies, the PSC-assembly, rated up to 1,000 V AC or 1,500 V DC.

In India, the Bureau of Indian Standards has adopted Part 1 as IS/IEC 61439 (Part 1):2020, identical to IEC 61439-1:2020 under single numbering and superseding the 2011 Indian edition. BIS also lists IS/IEC 61439 (Part 0):2014, the guidance to specifying assemblies, among its referred standards.

The 2020 editions changed things a tender copied from 2012 will miss:

Part 1 also carries a second corrigendum, COR2:2023. A specification that cites “IEC 61439” with no edition is inviting a 2011 design.

Who has to prove what: the original manufacturer or the panel builder?

IEC 61439 divides the burden of proof between two parties. ABB’s Technical Application Paper No. 11 defines the original manufacturer as “the organization that has carried out the original design, built and verified (through design verifications) the prototype of the assembly.” The assembly manufacturer is “the organization that takes the responsibility for the completed assembly and puts its name on the nameplate.”

The two can be the same company or different companies. A panel builder working under licence from an OEM system is typically the assembly manufacturer, building to the original manufacturer’s verified design and instructions. A panel builder with its own design is both.

The rule that matters most sits in the Siemens guide: if the original system is modified, “the design verifications must be provided for the modifications,” and the manufacturer making them “becomes the original manufacturer.” A panel builder who changes a busbar section, stretches a compartment beyond the verified range or substitutes an unverified breaker has taken on the design verification for that change. That is where a panel can quietly stop being an IEC 61439 assembly.

The same guide notes that the original manufacturer keeps the complete design verification record, including all test reports, calculations and records, throughout the product lifecycle, and is not required to forward it to the assembly manufacturer. So the buyer’s question to a panel builder is not “send me the test report.” It is “which verified system is this, which configuration, and who is the original manufacturer?”

What are the thirteen design verifications, and how can each be proven?

IEC 61439-1 lists thirteen design verifications, and allows three methods: testing, comparison with a tested reference design, and assessment by calculation or design rules. Not every method is permitted for every item. ABB’s Technical Application Paper No. 11 tabulates them:

Read the last three columns before accepting any claim. Clearances, creepage, power-frequency dielectric and mechanical operation can only be proven by test. Short-circuit withstand can be proven by test or by comparison with a tested reference design, never by assessment alone.

Why are temperature rise and short-circuit withstand the verifications to scrutinise?

Temperature rise and short-circuit withstand are the verifications to scrutinise because a cheaper build can undermine both without any visible change. A panel that looks identical on the shop floor can carry a busbar that tapers after the incomer, a lug that was badly crimped, or a compartment packed tighter than the verified design allowed.

Temperature rise is the verification with the most flexibility, and therefore the most room for abuse. All three methods are permitted, but assessment has limits. The ABB workbook The Standard IEC 61439 in Practice describes calculation routes up to 630 A and, using the IEC TR 60890 method, up to 1,600 A. Eaton’s white paper gives the 630 A route as applying to a single compartment only. Above 1,600 A with natural cooling, IEC 61439-2:2020 requires a combination of comparison with a reference design and calculation.

The group rated current in the 2020 edition exists because circuits heat each other. As Hemanshu Desai, CEO of New India Electricals Ltd, has put it, quality is what is inside the panel, because everything looks good coming off the shop floor and the difference only shows when it is wired up, fired up and loaded. Underspecification hides well: a panel bought light works perfectly at 500 or 800 A while the plant ramps up, and fails only when the plant reaches the full load it was bought for, a year or two later, outside warranty.

Short-circuit withstand is less forgiving. The ABB workbook lists the only cases where verification is not required: assemblies with a rated short-time withstand current or rated conditional short-circuit current not exceeding 10 kA, circuits protected by current-limiting devices with a cut-off current not exceeding 17 kA at the maximum prospective current at the incomer, and certain small auxiliary circuits. “All other circuits are to be verified.” A PCC rated for 50 kA falls outside all three exemptions unless every circuit behind it is current-limited.

What is the rated diversity factor, and why does it matter to the buyer?

The rated diversity factor is the ratio of the assumed loading of the outgoing circuits to their rated currents, which ABB’s Technical Application Paper No. 11 expresses as the sum of Ib divided by the sum of In. It tells the panel builder how many circuits will be loaded at once. Declared low, it allows a smaller busbar and a cheaper panel. Declared honestly, it reflects how your plant actually runs.

This is the buyer’s number to set, not the panel builder’s. A motor control centre feeding continuously running pumps, fans and conveyors runs at a high diversity factor. A distribution board feeding lighting and small power runs lower. If the enquiry leaves it blank, the quotation will fill it in, usually in the direction that reduces cost.

What do forms of separation and IP ratings actually prove?

Forms of internal separation describe how the busbars, functional units and terminals are partitioned from each other. ABB’s paper summarises them: Form 1 has no internal separation; Form 2 separates the busbars from the functional units; Form 3 also separates the functional units from each other; Form 4 also separates the terminals from each other, each with “a” and “b” variants. The higher forms are what allow one feeder to be isolated and worked on while its neighbours stay in service.

IEC 61439-2:2020 tightened the meaning. Where the form of separation is higher than 1, all parts within the functional unit compartment that remain live when the unit is switched off must now be protected to at least IPXXB. On a drive panel, where the DC bus holds charge after isolation, that requirement protects the technician who opens the compartment on a night shift.

The degree of protection of the enclosure is a design verification in its own right, clause 10.3, provable by test or assessment. Heat and ingress protection pull against each other: a higher IP rating keeps dust out and heat in. An IP55 panel with drives on a 50 degree Celsius rolling mill floor needs a deliberate thermal design, and filters nobody cleans are among the commonest causes of drive over-temperature trips we hear about. The 2020 edition’s temperature-rise route for actively cooled assemblies up to 1,600 A exists for exactly this case.

What must routine verification cover on every panel?

Routine verification must be carried out on every assembly to detect faults in materials and workmanship and to confirm proper functioning. The Siemens guide lists nine items, and the assembly manufacturer is responsible for the record:

1. Degree of protection provided by enclosures. Checked against the verified design, including gland plates, door seals and any cut-outs added during build.

2. Clearances and creepage distances. Particularly where site-specific components or cable terminations have been added.

3. Protection against electric shock and continuity of protective circuits. Every door and removable part bonded, every protective conductor continuous.

4. Incorporation of equipment. Components installed as the original manufacturer’s instructions require.

5. Internal electrical circuits and connections. Tightening torques and connection integrity checked, not assumed.

6. Terminals for external conductors. Suitable for the cable sizes and numbers the site will terminate.

7. Mechanical operation. Interlocks, withdrawable units and doors operated.

8. Dielectric properties. A dielectric test on the completed assembly.

9. Wiring, operational performance and function. The scheme proven to do what the drawings say.

The routine verification record belongs to your panel, by serial number. Ask for it at the factory acceptance test, not after dispatch.

How does New India Electricals Ltd build to this standard?

New India Electricals Ltd (NIEL) is an ABB Licensed System House and runs an ABB-licensed MV and LV panel assembly unit of 30,000 sq ft, with capacity of 50 panels a month and more than 70 trained engineers and technicians. Our low voltage panels are built on a modular system in which each compartment can be varied in width, height and depth, so direct on line, star delta, soft starter and autotransformer starters can sit in one MCC. That flexibility is exactly why the original manufacturer’s verified configuration range has to be respected on every build.

Our medium voltage panels carry CPRI and ERDA type-test certificates across 11 kV, 33 kV and 36 kV ratings under IEC 62271-200, a separate standard with separate tests. We make the same point to every buyer about any certificate, including ours: it is tied to the design and rating tested. A certificate for one product and one rating does not cover a different panel, as our guide to specifying medium voltage switchgear explains. For drive panels, the thermal side of this is covered in our piece on VFD panels, and for capacitor panels in our guide to APFC panels.

What should your panel builder prove before you place the order?

Use this checklist in the enquiry and at the factory acceptance test.

1. Name the standard and edition. Specify IEC 61439-1:2020 and IEC 61439-2:2020, or IS/IEC 61439 (Part 1):2020, not “IEC 61439” alone.

2. Identify the original manufacturer. Ask which verified assembly system the panel is built to, and who holds its design verification record.

3. Declare the ratings you need proven. Rated current of the assembly, group rated current of critical circuits, rated short-time withstand current and duration, rated peak withstand current, rated diversity factor, form of separation and IP.

4. Ask how temperature rise was verified. Test, comparison or assessment, and for which configuration. Assessment is not acceptable above its permitted limits.

5. Ask how short-circuit withstand was verified. Test or comparison with a tested reference design, for a rating equal to or above your prospective fault level.

6. List every deviation from the verified design. Any modification makes the panel builder the original manufacturer for that change, with its own verification to show.

7. Require routine verification records per serial number. All nine items, witnessed at the factory acceptance test where possible.

8. Require drawings and documentation. General arrangement and schematics for approval before manufacture, reissued as-built after, with handling, installation, operation and maintenance instructions.

9. State the real service conditions. Switchroom ambient in the worst month with ventilation assumed failed, altitude, dust and humidity, so temperature rise is verified for your site.

Get your LV panel verified before you order

Send us your single-line diagram, fault level at the incomer, and switchroom conditions. We will state how each rating is verified: by test, by comparison with a tested design, or by assessment.

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