BURN-BRITE 2.5A INTRINSICALLY SAFE POWER SUPPLY (ISPS) MK 2
Update: 20th December, 2021.
Burn Brite is fully engaged with ExTC and expects resolution of the ISPS Mk2 certification in January 2022.
Update: 10th November, 2021.
The original Applicant initiated Suspension of the Burn-Brite ISPS Mk2 Certificates of Conformity (CoC) covered the following:
- IECEx ITA 14.0005X
- IECEx TSA 13.0013X
The suspension and subsequent investigation have focused on the apparently disparate results from spark testing of the power supply by three separate IECEx accredited Test Laboratories (TLs).
Note: It is fundamental to the IECEx (and ANZEx) Equipment Schemes that the test results obtained by accredited TLs are not subject to independent confirmation, verification or question by any other party, and so are assumed to be ‘infallible’. In that context, the testing undertaken by accredited TLs that informed the issuing of two separate CoCs (and their revisions) is given significant credence.
The question, then, is how can different outcomes be achieved by different TLs at different times?
It is helpful to consider the test arrangement in sequential three parts:
- Equipment under Test (EUT) – in this case the Burn Brite ISPS Mk2 power supply.
- The electrical network connecting the EUT to the spark test apparatus.
- The Spark Test Apparatus (STA).
(1) The Equipment Under Test (ISPS Mk2)
The Manufacturer has undertaken comprehensive audits of all aspects of the procurement, manufacture, assembly and routine testing of the ISPS MK2 power supply, with no errors or omissions found. The EUT in the most recent testing is, as far as can be ascertained, the same as that tested previously under the various CoC updates. The Manufacturer’s Ex QAR is current, with no outstanding nonconformances, and zero nonconformances in the most recent audit.
The configuration of the EUT is determined by the TL’s Test Engineer and guided by the relevant standard. Some test configurations test the ISPS as a complete unit, others partition the circuit and/or introduce intentional faults into the arrangement. See IEC 60079.11 for details.
The Test Reports provided by the TLs usually describe the general test arrangement, however the detailed test arrangements are not typically provided in the Test Report. [These are retained in Laboratory notes by the TL and not made available to the Applicant.] In this context, it can be difficult to ensure that the separate tests conducted on each occasion are undertaken in the exact same way, leaving the potential for variability in testing and inconsistent test outcomes.
(2) The electrical network
Each of the previous spark testing sessions of the EUT have been undertaken with the same notional arrangements: lumped electrical elements (R, L and C) inserted between the ISPS and STA interconnected by laboratory cabling, with various instrumentation for measurement and monitoring.
Table 1 shows the resistance of various electrical network elements as measured by the Test Laboratories in recent testing:
|Element||Test Lab A||Test Lab B|
|Resistance of STA||0.12 Ω||0.1116 Ω|
|Inductance of STA||Not provided||0.82 μH|
|Resistance of connecting cables||0.05 Ω||0.0506 Ω|
|Inductance of connecting cables||Not provided||1.19 μH|
|Resistance of lumped inductor(s)||0.05 Ω for 28 μH|
0.13 Ω (for 105 μH)
|0.1348 Ω (28 μH)|
Table 1: Circuit parameters values used in recent STA tests by IECEx TLs.
The significance of the values in Table 1 can be appreciated by a recent experimental observation that an increase in resistance of 0.1 Ω in the electrical network in an otherwise identical test arrangement can be the difference between STA ignition and non-ignition.
The detailed parameters for test objects used in earlier issues of the Certificate of Conformity have not been able to be sourced.
It is readily apparent that the absence of detailed technical records of circuit parameters makes comparison of different test scenarios problematic.
If repeatability of test arrangements is to be assured, it is arguably most appropriate to parameterize a practical inductor in terms of its equivalent model:
- Pure inductance
- Series resistance
- Parallel capacitance
(Similar models can be described for capacitive elements.)
(3) The Spark Test Apparatus (STA)
The Spark Test Apparatus has been previously and widely acknowledged to have degrees of inherent uncertainty. The prescribed STA procedures seek to address these by various statistical strategies – for example testing for multiple/extended periods – to desensitize the results to the inherent vagaries of the test apparatus.
The uncertainty of the STA is something that must be accepted, pending the universal (IECEx) adoption of a more reliable test apparatus.
- Establishing repeatable test arrangements (and so test outcomes) by detailed measurements and records of test parameters, with a view to being able to corroborate test results between tests (at the same laboratory) and between Test Laboratories.
- Analyse and summarise the extensive IS entity parameter data received from Qld mine sites so as to identify a subset of ISPS entity parameters that will address the majority of use-cases to inform an interim supplementary certificate of conformity.
- Continue with the plan to issue an interim supplementary Certificate of Conformity within four weeks that will either:
- Confirm existing entity parameters
- Alter the existing entity parameter set and accommodate the majority of end-use cases.
Clarification of previous advice
Where a system contains both lumped inductances and lumped capacitances, IEC AS/NZS 60079.25 already places significant restrictions on permissible values and adds a substantial additional factor of safety for linear power supplies. Where both the lumped inductance and the lumped capacitance are greater than 1% of the respective output parameters Lo and Co of the IS power supply then IEC AS/NZS 60079.25 already requires that the permissible output parameters are both divided by two.
The Burn-Brite ISPS Mk2 is a nonlinear power supply. It is not necessary to de-rate the permissible output parameters at outlined above for linear supplies.
Where existing ISPS Mk2 installations have applied the de-rating, the resulting system will be more conservative that necessary. No further action is needed in such cases.
Initial Update: 18th October, 2021.
Temporary Voluntary Certificate Suspension
In accordance with IECEx OD 209 Ed 1.0 Clause 4.2.1, Burn-Brite has voluntarily initiated suspension of Certificate of Conformity IECEx ITA 14.0005X [INTRINSICALLY SAFE POWER SUPPLY V2], effective from 18th October, 2021.
Furthermore, Burn-Brite has voluntarily suspended manufacture of the ISPS from 15th October, 2021, which preceded suspension of the Certificate of Conformity.
The reason for suspension
Burn-Brite has recently been made aware of a spark test result from a Test Laboratory that is, prima facia, inconsistent with particular IS parameter sets previously established in compliance testing.
Burn-Brite is exercising an abundance of caution in suspending this Certificate of Conformity pending investigation.
Is there a safety issue with the power supplies already in use?
No, a safety issue does not exist with the power supplies already in use.
The investigation is only associated with the 12V 2.5A variant of the IS power supply, and then only associated with electrical loads where high inductance and very low resistance combine to present an effective short circuit. This type of load is generally impractical for a DC power supply in continuous operation as the power supply will electronically trip and reset.
Testing indicates the factor of safety for this highly specific load condition comfortably exceeds unity, and so is considered safe. [The default factor of safety is 1.5.]
What does the suspension mean?
The suspension is voluntary and (only) prevents Burn-Brite from continuing manufacture while the investigation is underway.
Under the IECEx Scheme rules, suspension of a certificate of conformity is very distinct from a cancellation of a certificate of conformity:
- Suspension means that new manufacture of the product is halted but use of existing products (manufactured before the suspension) in hazardous areas continues to be permitted.
- Cancellation means that existing product cannot be used in hazardous areas.
For avoidance of doubt, the certificate in question is suspended but is not cancelled.
Notwithstanding this provision, and in the interest of enhanced safety, Burn-Brite recommends that the technical guidance offered in this document be reviewed and considered as soon as is reasonably practical by end users.
As the suspension of manufacturing has preceded suspension of the Certificate of Conformity, Burn-Brite can assure the industry that there are no ISPS Mk2 products that are unable to continue to be used in the field.
What products are affected?
Certificate IECEx ITA 14.0005X lists several variants of the IS power supply, namely:
|159104||PSU IS MK2 IECEx 12VDC 2.5A|
|162087||PSU IS MK2 IECEx 12VDC 1.0A|
|162088||PSU IS MK2 IECEx 12VDC 1.5A
|162089||PSU IS MK2 IECEx 12VDC 2.0A|
|169804||PSU IS MK2 IECEx 12VDC 2.35A|
|171103||PSU IS MK2 IECEx 11.6VDC 2.5A|
|172742||PSU IS MK2 ATEX 12VDC 2.5A|
|172743||PSU IS MK2 ATEX 11.6VDC 2.5A|
|172744||PSU IS MK2 ATEX 12V 2.35A|
|172745||PSU IS MK2 ATEX 12V 2.0A|
|172746||PSU IS MK2 ATEX 12V 1.5A|
|172747||PSU IS MK2 ATEX 12V 1.0A|
The investigation is only associated with the 12V 2.5A variant of the IS power supply. However, all variants of the IS power supplies listed above are necessarily affected because they currently all appear on a single certificate of conformity. As a consequence, Burn-Brite are temporarily unable to manufacture any of those products listed.
What if a safety issue is discovered in the process of investigation?
The IECEx scheme has a rigorous and well-defined process that is automatically enacted if a safety issue is found or suspected. Those processes are executed independently of the manufacturer.
Burn-Brite has elected to voluntarily suspend the certificate and the manufacture of the affected product out of an abundance of caution.
What does this mean for field applications and existing IS audits?
All end users of equipment in hazardous areas are required to have IS audits and application documentation consistent with the requirements of IEC AS/NZS 60079.14 and IEC AS/NZS 60079.25 that verify the application parameters are within the bounds allowable under the Certificate of Conformity.
- For the applications where the input inductance of the field devices is small and the L/R ratio of the cable (Lc / Rc) is less than the published maximum Lo / Ro ratio there is no action required.Many applications utilising the IS power supply will include inductances that are associated with the input inductance of the field devices (Li) as well as the interconnecting cabling (Lc). In the majority of these cases, the input inductance of the field devices will be small or negligible and so calculation of the allowable inductance to resistance ratio of the cable (Lc / Rc) is straight forward. Frequently, input inductance (Li) is not quoted in documentation, and in these circumstances it can be assumed that the inductance is negligible. Where Li is less than 1% Lo, then the maximum permissible Lc / Rc is taken to be the Lo / Ro ratio published in the certificate of conformity for the power supply. The investigation underway does not draw the published Lo / Ro ratio in the existing certificate into question.
- Where an application includes lumped inductance, IEC AS/NZS 60079.25 Annex D provides additional guidance that must be followed to confirm acceptability. This is distinct from inductance that results from the distributed parameters of a cable, and there are two alternatives.
- Where the coil inductance (Li) is less than the power supply Lo, then the permitted inductance of the cable may be taken as the difference between Li and Lo and the system is acceptable.
- Any inductive coil has an inherent series resistance (Ri). If Li / Ri is less than the power supply Lo / Ro then the system is acceptable and the permitted inductance to resistance ratio for the cable (Lc / Rc) remains the same as the power supply Lo / Ro. It is possible to supplement (so increase) the coil series resistance Ri with an additional resistor to ensure Li / Ri is less than the power supply Lo / Ro on the proviso that the additional element conforms to the criteria for an infallible resistor and appropriate thermal considerations. Where the inductive apparatus conforms to either 2.1 or 2.2, there is no action required. Where the inductive apparatus does not conform to either of these requirements, then a more extensive analysis will have been undertaken to confirm acceptability. Please contact Burn-Brite for assistance with any clarification you may need.
- Where a system contains both lumped inductances and lumped capacitances, IEC AS/NZS 60079.25 already places significant restrictions on permissible values and adds a substantial additional factor of safety. On the rare occasion where both the lumped inductance and the lumped capacitance are greater than 1% of the respective output parameters Lo and Co of the IS power supply then IEC AS/NZS 60079.25 already requires that the permissible output parameters are both divided by two. It is unusual for field devices to have both inductive and capacitive input parameters which are significantly large. On those rare occasions where the permissible output parameters are both to be divided by two (as per IEC AS/NZS 60079.25 Annex A), again there is no action required. Please contact Burn-Brite for assistance with any clarification you may need.Where a system contains both lumped inductances and lumped capacitances, IEC AS/NZS 60079.25 already places significant restrictions on permissible values and adds a substantial additional factor of safety for linear power supplies. Where both the lumped inductance and the lumped capacitance are greater than 1% of the respective output parameters Lo and Co of the IS power supply then IEC AS/NZS 60079.25 already requires that the permissible output parameters are both divided by two.The Burn-Brite ISPS Mk2 is a nonlinear power supply. It is not necessary to de-rate the permissible output parameters at outlined above for linear supplies.
Where existing ISPS Mk2 installations have applied the de-rating, the resulting system will be more conservative that necessary. No further action is needed in such cases.
A certificate of conformity cannot remain in suspension indefinitely. Suspension is a temporary status, and Burn-Brite anticipate prompt re-instatement of the Certificate of Conformity once the investigation is completed.
The investigation is only associated with the 12V 2.5A variant of the IS power supply.
Burn-Brite has initiated the process to request a revised Certificate of Conformity that that will cover all power supply variants other than 12VDC, 2.5A. As soon as that revised certificate is available manufacturing of all variants other than 12VDC, 2.5A will resume.
Burn-Brite will notify the market and relevant parties as soon as manufacturing of these products has resumed, and are again available for purchase.
Manufacture of the 12VDC, 2.5A units will remain on hold until the suspension of certificate IECEx ITA 14.0005X is lifted.
Both cases will be expedited as a matter of priority.
What is the likely outcome of the investigation?
The two most likely outcomes of the investigation are:
- The suspended Certificate of Conformity is re-instated and manufacturing will resume.
- The suspended Certificate of Conformity is reinstated with a minor change to a subset of lumped inductance parameters. The investigation underway does not draw the published Lo / Ro ratio in the existing certificate into question, and so is unlikely to affect the vast majority of field applications.
What about my outstanding order of 2.5A IS power supplies?
The 2.5A power supply is one of Burn-Brite’s most popular products, and the voluntary suspension will affect several large orders from customers nearing delivery. Unfortunately, these deliveries must be suspended whilst the investigation is underway.
Our records clearly identify those customers affected by the manufacturing suspension, and they will be contacted directly by Burn-Brite representatives to receive regular updates as investigations continue.
Burn-Brite has not taken the decision to suspend the Certificate of Conformity lightly, and is exercising extreme caution in the interest of safety. Burn-Brite apologises for the disruption our voluntary suspension may cause, and will work closely with affected customers to minimise the disruption within the constraints of the IECEx processes now enacted.
Burn-Brite will publish regular industry updates on progress as we work toward resumption of our certificate.
Who to contact for clarifications or technical assistance?
There is a large installed base of Burn-Brite power supplies across the various mining jurisdictions in Australia. To ensure any enquiry related to our voluntary suspension is responded to promptly and efficiently, please use the dedicated email contact IS_Power@ampcontrolgroup.com
Copies of this document (be they printed or downloaded) are not controlled. Latest information and industry updates will be maintained electronically at:
Enquiries and requests for information that are not related to our voluntary suspension should continue to use our normal electronic product customer service portal CustomerService@ampcontrolgroup.com