An update on CE Marking Electrical Cable

CE Marking Wire and Cable

A picture showing a selection of wire and cable products
Domest­ic and European Wire and Cable Products

In an earli­er post, I wrote about the require­ments for CE Mark­ing wire and cable and dis­cussed the <HAR> mark. In 2016, the Con­struc­tion Products Reg­u­la­tion 305/2011 (CPR) came into effect, repla­cing the Con­struc­tion Products Dir­ect­ive 89/106/EEC. The CPR included pro­vi­sions cov­er­ing any kind of mater­i­als that could be used in con­struc­tion, and that includes elec­tric­al cables.

A New Standard under the CPR

A new stand­ard was approved, EN 50575, cov­er­ing the char­ac­ter­ist­ics of power, con­trol and com­mu­nic­a­tion cables used in per­man­ent install­a­tions in build­ings. EN 50575 cov­ers the reac­tion of cables to fire. The stand­ard provides require­ments for four char­ac­ter­ist­ics: flame spread, smoke gen­er­a­tion, the form­a­tion of mol­ten droplets and acid con­tent. The res­ult is a new set of mark­ings for cables covered by the stand­ard, includ­ing CE Mark­ing. Also required by the CPR is a Declar­a­tion of Per­form­ance, not a Declar­a­tion of Con­form­ity. The Declar­a­tion of Per­form­ance provides dif­fer­ent inform­a­tion than that found in a Declar­a­tion of Con­form­ity and they are NOT inter­change­able.

Application of EN 50575

EN 50575 only applies to cables or wir­ing products inten­ded for use in con­struc­tion. It should not be applied to wir­ing mater­i­als used for intern­al wir­ing of appli­ances and products. These products are out­side the scope of the CPR and there­fore are also out­side the scope of EN 50575.

Conclusions

  • Cables used for per­man­ent install­a­tion in build­ings must be CE Marked start­ing 1-Jul-2017
  • Wire and cable products used in machines and appli­ances are not affected by EN 50575, and there­fore should not be CE Marked
  • Cables used to inter­con­nect machinery and which are per­man­ently installed into build­ing infra­struc­ture (e.g., Eth­er­net cables and oth­er inter­con­nect­ing cables run through build­ing struc­tures in per­man­ent wire­ways or in plen­um spaces) require CE Mark­ing as of 1-Jul-17
  • Wire and cable products, like line-cord assem­blies, for example, require a CE Mark because they are com­plete products and are covered by a spe­cif­ic EN Stand­ard under the Low Voltage Dir­ect­ive.

Here’s a good sum­mary of the new require­ments and an explan­a­tion of the new mark­ings in a video by Gen­er­al Cable. Full dis­clos­ure: we have no rela­tion­ship with Gen­er­al Cable or any oth­er wire and cable man­u­fac­turer.

Need more help? Get in touch!

ISO 13849 – 1 Analysis — Part 6: CCF — Common Cause Failures

This entry is part 6 of 9 in the series How to do a 13849 – 1 ana­lys­is

What is a Common Cause Failure?

There are two sim­il­ar-sound­ing terms that people often get con­fused: Com­mon Cause Fail­ure (CCF) and Com­mon Mode Fail­ure. While these two types of fail­ures sound sim­il­ar, they are dif­fer­ent. A Com­mon Cause Fail­ure is a fail­ure in a sys­tem where two or more por­tions of the sys­tem fail at the same time from a single com­mon cause. An example could be a light­ning strike that causes a con­tact­or to weld and sim­ul­tan­eously takes out the safety relay pro­cessor that con­trols the con­tact­or. Com­mon cause fail­ures are there­fore two dif­fer­ent man­ners of fail­ure in two dif­fer­ent com­pon­ents, but with a single cause.

Com­mon Mode Fail­ure is where two com­pon­ents or por­tions of a sys­tem fail in the same way, at the same time. For example, two inter­pos­ing relays both fail with wel­ded con­tacts at the same time. The fail­ures could be caused by the same cause or from dif­fer­ent causes, but the way the com­pon­ents fail is the same.

Com­mon-cause fail­ure includes com­mon mode fail­ure, since a com­mon cause can res­ult in a com­mon man­ner of fail­ure in identic­al devices used in a sys­tem.

Here are the form­al defin­i­tions of these terms:

3.1.6 com­mon cause fail­ure CCF

fail­ures of dif­fer­ent items, res­ult­ing from a single event, where these fail­ures are not con­sequences of each oth­er

Note 1 to entry: Com­mon cause fail­ures should not be con­fused with com­mon mode fail­ures (see ISO 12100:2010, 3.36). [SOURCE: IEC 60050?191-am1:1999, 04 – 23.] [1]

 

3.36 com­mon mode fail­ures

fail­ures of items char­ac­ter­ized by the same fault mode

NOTE Com­mon mode fail­ures should not be con­fused with com­mon cause fail­ures, as the com­mon mode fail­ures can res­ult from dif­fer­ent causes. [lEV 191 – 04-24] [3]

The “com­mon mode” fail­ure defin­i­tion uses the phrase “fault mode”, so let’s look at that as well:

fail­ure mode
DEPRECATED: fault mode
man­ner in which fail­ure occurs

Note 1 to entry: A fail­ure mode may be defined by the func­tion lost or oth­er state trans­ition that occurred. [IEV 192 – 03-17] [17]

As you can see, “fault mode” is no longer used, in favour of the more com­mon “fail­ure mode”, so it is pos­sible to re-write the com­mon-mode fail­ure defin­i­tion to read, “fail­ures of items char­ac­ter­ised by the same man­ner of fail­ure.”

Random, Systematic and Common Cause Failures

Why do we need to care about this? There are three man­ners in which fail­ures occur: ran­dom fail­ures, sys­tem­at­ic fail­ures, and com­mon cause fail­ures. When devel­op­ing safety related con­trols, we need to con­sider all three and mit­ig­ate them as much as pos­sible.

Ran­dom fail­ures do not fol­low any pat­tern, occur­ring ran­domly over time, and are often brought on by over-stress­ing the com­pon­ent, or from man­u­fac­tur­ing flaws. Ran­dom fail­ures can increase due to envir­on­ment­al or pro­cess-related stresses, like cor­ro­sion, EMI, nor­mal wear-and-tear, or oth­er over-stress­ing of the com­pon­ent or sub­sys­tem. Ran­dom fail­ures are often mit­ig­ated through selec­tion of high-reli­ab­il­ity com­pon­ents [18].

Sys­tem­at­ic fail­ures include com­mon-cause fail­ures, and occur because some human beha­viour occurred that was not caught by pro­ced­ur­al means. These fail­ures are due to design, spe­cific­a­tion, oper­at­ing, main­ten­ance, and install­a­tion errors. When we look at sys­tem­at­ic errors, we are look­ing for things like train­ing of the sys­tem design­ers, or qual­ity assur­ance pro­ced­ures used to val­id­ate the way the sys­tem oper­ates. Sys­tem­at­ic fail­ures are non-ran­dom and com­plex, mak­ing them dif­fi­cult to ana­lyse stat­ist­ic­ally. Sys­tem­at­ic errors are a sig­ni­fic­ant source of com­mon-cause fail­ures because they can affect redund­ant devices, and because they are often determ­in­ist­ic, occur­ring whenev­er a set of cir­cum­stances exist.

Sys­tem­at­ic fail­ures include many types of errors, such as:

  • Man­u­fac­tur­ing defects, e.g., soft­ware and hard­ware errors built into the device by the man­u­fac­turer.
  • Spe­cific­a­tion mis­takes, e.g. incor­rect design basis and inac­cur­ate soft­ware spe­cific­a­tion.
  • Imple­ment­a­tion errors, e.g., improp­er install­a­tion, incor­rect pro­gram­ming, inter­face prob­lems, and not fol­low­ing the safety manu­al for the devices used to real­ise the safety func­tion.
  • Oper­a­tion and main­ten­ance, e.g., poor inspec­tion, incom­plete test­ing and improp­er bypassing [18].

Diverse redund­ancy is com­monly used to mit­ig­ate sys­tem­at­ic fail­ures, since dif­fer­ences in com­pon­ent or sub­sys­tem design tend to cre­ate non-over­lap­ping sys­tem­at­ic fail­ures, redu­cing the like­li­hood of a com­mon error cre­at­ing a com­mon-mode fail­ure. Errors in spe­cific­a­tion, imple­ment­a­tion, oper­a­tion and main­ten­ance are not affected by diversity.

Fig 1 below shows the res­ults of a small study done by the UK’s Health and Safety Exec­ut­ive in 1994 [19] that sup­ports the idea that sys­tem­at­ic fail­ures are a sig­ni­fic­ant con­trib­ut­or to safety sys­tem fail­ures. The study included only 34 sys­tems (n=34), so the res­ults can­not be con­sidered con­clus­ive. How­ever, there were some start­ling res­ults. As you can see, errors in the spe­cific­a­tion of the safety func­tions (Safety Require­ment Spe­cific­a­tion) res­ul­ted in about 44% of the sys­tem fail­ures in the study. Based on this small sample, sys­tem­at­ic fail­ures appear to be a sig­ni­fic­ate source of fail­ures.

Pie chart illustrating the proportion of failures in each phase of the life cycle of a machine, based on data taken from HSE Report HSG238.
Fig­ure 1 – HSG 238 Primary Causes of Fail­ure by Life Cycle Stage

Handling CCF in ISO 13849 – 1

Now that we under­stand WHAT Com­mon-Cause Fail­ure is, and WHY it’s import­ant, we can talk about HOW it is handled in ISO 13849 – 1. Since ISO 13849 – 1 is inten­ded to be a sim­pli­fied func­tion­al safety stand­ard, CCF ana­lys­is is lim­ited to a check­list in Annex F, Table F.1. Note that Annex F is inform­at­ive, mean­ing that it is guid­ance mater­i­al to help you apply the stand­ard. Since this is the case, you could use any oth­er means suit­able for assess­ing CCF mit­ig­a­tion, like those in IEC 61508, or in oth­er stand­ards.

Table F.1 is set up with a series of mit­ig­a­tion meas­ures which are grouped togeth­er in related cat­egor­ies. Each group is provided with a score that can be claimed if you have imple­men­ted the mit­ig­a­tions in that group. ALL OF THE MEASURES in each group must be ful­filled in order to claim the points for that cat­egory. Here’s an example:

A portion of ISO 13849-1 Table F.1.
ISO 13849 – 1:2015, Table F.1 Excerpt

In order to claim the 20 points avail­able for the use of sep­ar­a­tion or segreg­a­tion in the sys­tem design, there must be a sep­ar­a­tion between the sig­nal paths. Sev­er­al examples of this are giv­en for clar­ity.

Table F.1 lists six groups of mit­ig­a­tion meas­ures. In order to claim adequate CCF mit­ig­a­tion, a min­im­um score of 65 points must be achieved. Only Cat­egory 2, 3 and 4 archi­tec­tures are required to meet the CCF require­ments in order to claim the PL, but without meet­ing the CCF require­ment you can­not claim the PL, regard­less of wheth­er the design meets the oth­er cri­ter­ia or not.

One final note on CCF: If you are try­ing to review an exist­ing con­trol sys­tem, say in an exist­ing machine, or in a machine designed by a third party where you have no way to determ­ine the exper­i­ence and train­ing of the design­ers or the cap­ab­il­ity of the company’s change man­age­ment pro­cess, then you can­not adequately assess CCF [8]. This fact is recog­nised in CSA Z432-16 [20], chapter 8. [20] allows the review­er to simply veri­fy that the archi­tec­tur­al require­ments, exclus­ive of any prob­ab­il­ist­ic require­ments, have been met. This is par­tic­u­larly use­ful for engin­eers review­ing machinery under Ontario’s Pre-Start Health and Safety require­ments [21], who are fre­quently work­ing with less-than-com­plete design doc­u­ment­a­tion.

In case you missed the first part of the series, you can read it here. In the next art­icle in this series, I’m going to review the pro­cess flow for sys­tem ana­lys­is as cur­rently out­lined in ISO 13849 – 1. Watch for it!

Book List

Here are some books that I think you may find help­ful on this jour­ney:

[0]     B. Main, Risk Assess­ment: Basics and Bench­marks, 1st ed. Ann Arbor, MI USA: DSE, 2004.

[0.1]  D. Smith and K. Simpson, Safety crit­ic­al sys­tems hand­book. Ams­ter­dam: Elsevi­er­/But­ter­worth-Heine­mann, 2011.

[0.2]  Elec­tro­mag­net­ic Com­pat­ib­il­ity for Func­tion­al Safety, 1st ed. Steven­age, UK: The Insti­tu­tion of Engin­eer­ing and Tech­no­logy, 2008.

[0.3]  Over­view of tech­niques and meas­ures related to EMC for Func­tion­al Safety, 1st ed. Steven­age, UK: Over­view of tech­niques and meas­ures related to EMC for Func­tion­al Safety, 2013.

References

Note: This ref­er­ence list starts in Part 1 of the series, so “miss­ing” ref­er­ences may show in oth­er parts of the series. The com­plete ref­er­ence list is included in the last post of the series.

[1]     Safety of machinery — Safety-related parts of con­trol sys­tems — Part 1: Gen­er­al prin­ciples for design. 3rd Edi­tion. ISO Stand­ard 13849 – 1. 2015.

[2]     Safety of machinery – Safety-related parts of con­trol sys­tems – Part 2: Val­id­a­tion. 2nd Edi­tion. ISO Stand­ard 13849 – 2. 2012.

[3]      Safety of machinery – Gen­er­al prin­ciples for design – Risk assess­ment and risk reduc­tion. ISO Stand­ard 12100. 2010.

[8]     S. Jocelyn, J. Bau­doin, Y. Chin­ni­ah, and P. Char­pen­ti­er, “Feas­ib­il­ity study and uncer­tain­ties in the val­id­a­tion of an exist­ing safety-related con­trol cir­cuit with the ISO 13849 – 1:2006 design stand­ard,” Reliab. Eng. Syst. Saf., vol. 121, pp. 104 – 112, Jan. 2014.

[17]      “fail­ure mode”, 192 – 03-17, Inter­na­tion­al Elec­tro­tech­nic­al Vocab­u­lary. IEC Inter­na­tion­al Elec­tro­tech­nic­al Com­mis­sion, Geneva, 2015.

[18]      M. Gen­tile and A. E. Sum­mers, “Com­mon Cause Fail­ure: How Do You Man­age Them?,” Pro­cess Saf. Prog., vol. 25, no. 4, pp. 331 – 338, 2006.

[19]     Out of Con­trol — Why con­trol sys­tems go wrong and how to pre­vent fail­ure, 2nd ed. Rich­mond, Sur­rey, UK: HSE Health and Safety Exec­ut­ive, 2003.

[20]     Safe­guard­ing of Machinery. 3rd Edi­tion. CSA Stand­ard Z432. 2016.

[21]     O. Reg. 851, INDUSTRIAL ESTABLISHMENTS. Ontario, Canada, 1990.

Five things you need to know about CE Marked Wire and Cable

Wire is simple right? Maybe not! Here are the top five things to know when select­ing wire and cable products for use in designs that will be CE Marked:

  1. Wire and cable products sold in the EU must be CE Marked under the Low Voltage Dir­ect­ive, and MAY bear BOTH the CE Mark and the HAR mark. The HAR mark may only be applied by man­u­fac­tur­ers that have met the require­ments for the use of the HAR mark. More inform­a­tion on the HAR mark. 

    Picture of the HAR Mark.
    The HAR Mark
  2. The HD 21.X and HD 22.X Har­mon­iz­a­tion Doc­u­ments pre­vi­ously used for determ­in­ing com­pli­ance and apply­ing the CE Mark are being replaced by the EN 50525.X fam­ily of stand­ards start­ing on 2014-01-17. See the list.
  3. Wire and Cable products with Declar­a­tions of Con­form­ity that refer to older ver­sions of the Low Voltage Dir­ect­ive, or that refer to HD doc­u­ments that have been super­seded are NO LONGER COMPLIANT.
  4. Wire and Cable products used in “large-scale” machine tools and fixed install­a­tions do not need to meet WEEE require­ments.
  5. Design­ers are not required to use CE Marked wire and cable products in CE Marked Products.

Need to know more? Check out this art­icle!