Let’s say you’ve designed a newproduct, and your marketing department and legal beagles say,“We need safety certification to

sell it. And furthermore, we need it yesterday.”

Get the picture? You may think theproduct is ready and should have notrouble passing safety testing for certifi-cation. You also may think the testingand certification process is a mere for-mality and that you needn’t worry.

But did you know that if a productfails a single test,uses a noncertified crit-ical component, has a wrong label, or ismissing a caution symbol, the product isnot certifiable and may not ship? Thegood news is that safety certification isnot as complex as it once was.You justneed to familiarize yourself with theprocess and follow a few simple rules.

The safety certification process I’lloutline applies to many products, includ-ing Information Technology Equipment(IEC 60950-1) and Test & MeasurementEquipment (IEC 61010-1). Figure 1outlines the general process. The terms“third-party,”“agency,”and “certificationbody”are equivalent;all are government-accredited safety testing and certificationorganizations.

Preparation is thekey to limitingproduct redesignand obtainingsafety certificationson time.

SAFETY CERTIFICATIONfor the T&M WORLD

DAVID LOHBECK, NATIONAL INSTRUMENTS, AUSTIN, TX

Productships with

safety mark

Manufacturer CertificationBody

Certification and Mark

Identify safety-critical

components and get certificates

Verify components andconstruction anddocumentation

Safety testsperformed

Submit testsample, docs, andPO to cert body

Request andreceive quotefrom cert body

Pass? Pass?

Test sample,documentation,

PO received(Note 1)

Safety testsperformed

Deviation letterissued

(Notes 4 and 5)

Components,construction, anddocumentation

evaluation

Certificate andtest report issued

by the agency (Note 4)

Early authorizationletter issued by

the agency(Note 6)

(Note 2)

(Note 3)

No

YesNo NOTES:1. Time "starts" after receipt of test sample, all documentation, and PO by the certification body.

2. Preliminary evaluation findingsissued by agency when applicable.

3. Deviation letter (negativeresults) sent to manufacturer.

4. Time "ends" when the deviation letter or certificationis issued by the agency.

5. Additional costs may be incurred for resubmittal and testing.

6. Agency may allow manufacturer to affix safety mark on product before certificate issued based on early authorization letter.

Yes

FIGURE 1. Achieving a certification mark involves many steps, so manufacturersshould start the process long before the final product is built.

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SAFETY TEST

(continued)

Why Safety Certification?Safety certification protects the consumerand provides manufacturers with evi-dence of compliance. Certification is anattestation from an impartial testing bodythat a product has been evaluated andfound to comply with specific standards.Certification allows manufacturers toaffix safety marks to products as visualconformity evidence; marks include ULor CSA marks for North America, andVDE,TUV,or Demko marks for Europe.Safety certificates and marks indicate duediligence and are a manufacturer’s best de-fense should the safety of a product comeinto question by customers, competitors,or market-surveillance authorities.

International (IEC) standards are thefocus of safety conformity and form thebasis for other standards, such as thosepromulgated by the two primary types ofcertification bodies: Nationally Recog-nized Testing Laboratories (NRTL),which are qualified by OSHA in the US,and Notified Bodies, which are accred-ited by the European Commission in Eu-rope. UL and CSA are NRTLs, whileVDE, TUV, and Demko are NotifiedBodies.

Note that a European directive onproduct safety requires that many electri-cal products carry the European Confor-mity (CE) marking.But a CE mark is thesupplier’s self-declaration (self-test) sym-bol.CE is not an approval, certification,ormark from an independent certificationbody. European customers also may ex-pect VDE,TUV, or Demko marks on theproducts they purchase.

Safety assessment phasesStandards represent the minimum accep-tance criteria for safety assessment andcertification.You should familiarize your-self with the relevant standards in order todesign products for safety compliance.Certification bodies perform safety as-sessments in three phases:

● Components and construction. The firstassessment criteria is verification ofsafety-critical components—those thattypically see hazardous voltages that affectthe safety of the product, surroundings,and user. Safety marks on a componentare evidence that the component meetssafety standards. The certification bodyalso reviews the product’s construction

and user documentation for complianceto safety standards.

● Testing. Next, the certification bodyperforms safety testing on the product.Which safety tests the agency performsdepend on the product’s voltage andpower rating, design complexity, compo-nents, operating environment, and otherfactors.

● Test report and certification. After achiev-ing successful results, the certificationbody issues a signed test report and cer-tificate to the manufacturer.The certifi-

cate lists the product manufacturer’sname, factory(ies), model(s) tested, safetystandard(s), and ratings.The manufacturercan then apply the certification body’smark to the product.

Components and constructionA product containing just one wrongsafety-critical component—such as apower supply, optoisolator, fuse, relay, orconnector—will be found noncompli-ant. Thus, when selecting safety-criticalcomponents,you should look for ones af-fixed with safety marks and certificates.UL/CSA and IEC/EN standards are not

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SAFETY TEST

TECHNICAL DATACOMPONENT TYPE MANUFACTURER AND RATINGS PER SAFETY(DRAWING REFERENCE (NAME/LOGO MANUFACTURER’S CERTIFICATE AND MARKSOR LOCATION) ON PART) PART NUMBER MARKINGS (EVIDENCE)

Power supply (PS1) XYZ Corp. X1234-X-Y Input: 100–240 VAC, UL-R (QQFU2),5 A, 50/60 Hz; CSA, TUV,Outputs: 5 V/20 A, CB cert #123410 V/5 A; 20 cfmrequired for 35ºC operation

Inlet/filter/fuse ZYX Inc. Z-321-10A 250 VAC, 10 A, CSA, VDEholder (J1) 50/60 Hz

● ● ● ● ●

● ● ● ● ●

● ● ● ● ●

Table 1. Safety-critical components list

TEST PURPOSE PROCEDURE1 PASS/FAIL CRITERIA1

Input Used to check rating Measure power or current Measured current on label. Also used to during operation with max value shall notestablish rating. Test load; ±10% voltage rating exceed 10% of monitors the product’s (range). Suggestion: spec rating on label.power and voltage the product’s rating at during testing in normal about 10% above measured operation and fault current value for the user conditions. documentation and label.

Dielectric Dielectric, aka hipot, Primary to secondary No breakdown withstand stresses the product's (double) 2300 Vrms/ (arc-over) at AC or

insulation system (spacings, 3250 VDC, 1 min; DC voltage. (Repeatmaterials) to verify high Primary to ground dielectric withstand voltage withstand from (basic) 1350 Vrms/ test after eachprimary to ground and 1900 VDC, 1 min abnormal test;secondary. Protects user from (300 V CAT II). Test basic value.)hazardous voltage breakdown. performed after

humidity preconditioningand when product is well heated.

● ● ● ●

● ● ● ●

● ● ● ●

Table 2. Safety Test Examples

Note:1. Refer to the standards for more information on test procedures and pass/fail criteria.

See the online version of this article at www.tmworld.com/archives for a more detailed version of these tables.

34 ENTER 20 AT TMWORLD.COM/TIX

harmonized for many components, soyou may need two marks to verify a com-ponent meets US and EU requirements.No marks at all suggest a component isnot certified for any location!

Always verify a supplier’s safety claims.Statements such as “designed to meet . . .”or “in accordance with . . .” are only self-declarations and usuallymean a component is notcertified. You will need acopy of a component’s cer-tificate to verify component number, rat-ing, standard applied, and restrictions foruse. The component’s rating must meetan end product’s rating for use.Check thecertificate and look for the mark early.When in doubt, have a substitute ready.

Many certification bodies use theSafety-Critical Components List (Table1) to identify and check componentsafety. When submitting a product fortesting, you should use the list to identifyeach part by the component name, man-ufacturer, part number, and rating. Indi-cate safety marks in the last column. Inaddition to completing the list, youshould obtain certificates as backup, andthen submit the list and certificates to thecertification body for product testing.

To conform to the safety standards, aproduct must be constructed to protectagainst a number of hazards—shock,fire, heat, mechanical, radiation, explo-sion—and must be resistant to impact,and in some cases moisture and liquids.Values above 30 Vrms and 42.4 Vp or 60VDC are considered to be hazardous livevoltages. For such voltages, protectionagainst electric shock and fire must bemaintained in normal and single-faultconditions—hazardous voltage circuitsmust not be accessible via test finger orpin. Moving parts must not crush, cut,pierce, or severely pinch the operator’sskin. Enclosure construction, especiallybottom openings, must limit the spreadof fire.

TestingTesting is a critical part of the certifica-tion process and the final checkpoint.Even when a product meets the compo-nent and construction requirements, itmay fail safety testing. The tests theagency performs depend on the product’sfunction and its operating environment.Tests mandated by a standard are referred

to as Type Tests and are carried out on arepresentative product sample. Theagency performs the tests on a productassembled for normal use in the least fa-vorable conditions. Any tests that maydamage the product are performed last.

Safety testing, such as dielectric (orhipot) testing, is required in addition to—

not in place of—compo-nent certification and con-struction requirements. Aproduct must meet all com-

ponent,construction,and testing require-ments together before it is consideredsafety compliant.

To minimize the chance of failure, youshould arrange for safety pretests beforesubmitting a product to a test body forcertification. Examples of safety tests areshown in Table 2.

Preliminary evaluation—the fasttrack to certificationCompliance with safety standards shouldbe a consideration at every stage of aproduct’s development. Unfortunately,many companies wait to submit their“latest and greatest” model for testing,thinking that safety certification is one ofthe last steps taken before shipping aproduct. Safety certification may be oneof the last steps in the design process asflow charts go, but it is a step that shouldbe taken much earlier.

Many of those who wait to submittheir “final product” and then find that itfails to meet safety standards say that ifthey had only known of the deviationssooner, they could have fixed them dur-ing the product’s developmental stages.Waiting only delays the day of productcompliance.

To minimize guesswork and obtainanswers early, you should submit a prod-uct to the testing agency for a prelimi-nary evaluation of components and con-struction. The cost is typically less thanhalf the cost of a full assessment. In lieuof the finished product, you can submit aprototype for preliminary evaluation.(See the online version of this article atwww.tmworld.com/archives to down-load a checklist of what you can expectto submit.)

Changes within safety extra-low volt-age (SELV; <42.4 Vp or <60 VDC) cir-cuits usually have no effect on safety, sodon’t wait for SELV revisions to submit.

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SAFETY TEST

www.tmworld.com TEST & MEASUREMENT WORLD36 AUGUST 2004

Remember to provide explanations ofany planned corrections or updates sothe testing body may review how the po-tential changes could affect the product’ssafety.The agency engineer evaluates theproduct and user documentation and, ifrequested,can also perform key tests if heor she suspects a failure could occur.

The agency issues a findings letterupon completion.You then correct thedeviations and resubmit for a full assess-ment, testing, and certification. If the de-viations are minor, the agency may ac-cept your proposed corrections viadrawings or letter without a new sampleor further testing.

After initiating a project, you shouldestablish a direct relationship with theagency engineer. Make sure you discussexpectations and how the project willproceed.Don’t be afraid to ask questions;this is your chance to learn.

The agency typically forwards its find-ings to you after the assessment is com-plete.You can, however, ask the engineerto contact you immediately if he or shefind major safety deviations. This way,you may be able to correct problems be-fore the project is completed and endwith a passing result. The secret here isgood communication and quick re-sponse to questions and issues.

You can avoid many pitfalls, time de-lays, and costly redesign when you un-derstand the standards and become famil-iar with the safety certification process.Verifying components and constructionsafety and performing safety tests prior tosubmittal increase the chance of certifica-tion the first time through. The lessonsyou’ll learn by going through the safetycertification process typically carry overto new products, making them easier tocertify. T&MW

FOR FURTHER READING“Product Certification,” National Instru-ments, www.ni.com/certification.

David Lohbeck is compliance engineeringmanager at National Instruments in Austin,TX. Previously, he has worked for Motorola,Dell, and TUV in the field of internationalproduct safety, machine safety, and electro-magnetic compatibility (EMC). He received aBS from Arizona State University. Lohbeck isauthor of CE Marking Handbook: A PracticalApproach to Global Safety Certification. E-mail: dave.lohbeck@ni.com.

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