IEC61010 creepage application on measuring device - Page 1
Forum section: electronics / projects

author: Cyclone1
author_rank: Newbie
timestamp: September 04, 2024, 02:16:26 am
content: I am currently working on a measuring device project that which I also need to dab into safety isolation stuff. Being one without prior knowledge in IEC 61010, I have been reading the standard over and over again to learn about it. After getting used to it, I find myself lost because some of the requirement is really difficult to attain.To gain some insight, I actually tore down a few of 1000V benchtop DMM from a few well known brand, what I found from their design had confused me further which made me think if I have misunderstood the standard. Being no one to consult to, I hope I could get some info from this post.Here is where I have problem: IEC61010 requires 5mm/7.1mm/10mm created from material group I/II/III respectively for working voltage of 1000VDC to form a basic insulation. What I found from the instrument tear down is that, all the input switching relays, mechanical switches or optocoupler to drive the input MOSFET do not conform to this requirement. I checked one relay datasheet of one of the dmm, the datasheet only specified 2.5mm with no mention of material group, (which in this case should be defaulted to Grp III thus 10mm creepage) but is being used to switch the input 1000V. Relay is only one example. Not only they are not basic insulation, under single fault condition, wouldn't it become a shock hazard?My understanding is that the safety body such as TUV or CSA not only require the product to be tested and passed, the design shall also meet the required clearance/creepage on paper as well. How do these mfg manage to get through this? Did I somehow misunderstood the standard?

author: Whales
author_rank: Super Contributor
timestamp: September 04, 2024, 02:37:14 am
content: What's the multimeter?I've seen some labelled with multiple voltage specs. Eg the CAT voltage being 250V but the "max" voltage being 1000V.

author: Someone
author_rank: Super Contributor
timestamp: September 04, 2024, 03:47:48 am
content: Quote from: Cyclone1 on September 04, 2024, 02:16:26 amYou misunderstand. Creepage/clearance are for protection of the user, not for operational. The safety standards basically say "the device will not harm the user", they do not say "the device will continue to operate".

author: floobydust
author_rank: Super Contributor
timestamp: September 04, 2024, 04:05:21 am
content: Quote from: Someone on September 04, 2024, 03:47:48 amNot quite - a multimeter cannot fail to properly display a hazardous live voltage measurement. Otherwise, that would endanger the user. You think it's safe, power off etc. but it isn't.Recalls have been issued if it reboots/crashes/displays nonsense or zero when HV is present on the voltage functions.

author: Someone
author_rank: Super Contributor
timestamp: September 04, 2024, 08:05:37 am
content: Quote from: floobydust on September 04, 2024, 04:05:21 amAfter a maximum transient/impulse ? Please do refer to the clause which requires correct operation after withstand testing (or transient/impulse in service).Remember why clearances and creepage are required:"clearances and creepage distances between accessible parts and hazardous live parts shall meet the requirements of 6.7 and the applicable requirements for basic insulation"Nowhere is clearance and creepage required between arbitrary points inside the system, only between accessible and other points.

author: Neilm
author_rank: Super Contributor
timestamp: September 04, 2024, 06:14:55 pm
content: Basic creepage is required for 2 reasons, 1 is to the user to prevent electric shock, the other is between conductors for protection against fire & explosion.The requirement for the latter can be reduced if it is after a suitable fuse (see the flow diagram in section 9). The idea being that if it does breakdown the fuse will open and offer protection.

author: tooki
author_rank: Super Contributor
timestamp: September 04, 2024, 06:26:10 pm
content: Quote from: Someone on September 04, 2024, 08:05:37 amI don't think that's what is required. What I think floobydust is saying is thatifthe multimeter continues to show a number after withstand testing, then that number is required to be correct. So if the meter fails, it needs to fail tonotdisplaying a number.

author: floobydust
author_rank: Super Contributor
timestamp: September 04, 2024, 08:01:43 pm
content: OP I notice every discussion on this forum about safety standards derails into a mud slinging, personal attack so it's not possible to explain, teach or discuss the details.Instead of hammering it out, time is wasted refuting noise. It's too bad, you'll have to learn it the hard, expensive way. It's not easy, I've taught juniors and other engineers.Some struggle and never "get it". Are you a PE?I don't know the make/model of multimeter, relay etc. you are looking at. Knowing the correct 61010 spacings table to apply is very important and takes a lot of work to get there.Bench multimeters have minimal transient ratings, common is "Cat. II 300V" for 2,500V transient withstand requirement.With signal relays, there are the contact spacings plus the contact-coil spacing to consider. They typically come after the DMM input protection circuit and will not see the full impulse.One starting point is a block diagram of the product showing the different voltage barriers between boundaries/circuit sections.An important question to ask is "what is the method of protection against electric shock and fire?" It can be insulation, grounding, isolation etc.A bench multimeter has two sources of hazardous energy - mains power and the measured input.If you don't meet a spacings requirement, a certifier will bridge the nodes and see what happens. Think about that.Quote from: Someone on September 04, 2024, 08:05:37 amWhich clause requires "correct operation"? You've got to be kidding. After a test, product operation and status is evaluated. This is the pass criteria.Again- I am saying if the multimeter fails to display a hazardous voltage, it is unsafe and endangering the user. Hurting someone and the litigation is the second clause.

author: Someone
author_rank: Super Contributor
timestamp: September 04, 2024, 11:45:27 pm
content: Quote from: floobydust on September 04, 2024, 08:01:43 pmThen it should be trivial to point to the cause which requires that. Functional specifications and correct operation is not in 61010, that is usually a business decision a layer above. 4.4.4 only requires that the device still be safe after testing, not that it correctly function. You can have all sorts of arcing and reduced clearances in the measurement path, if they don't expose the user to any hazard.

author: floobydust
author_rank: Super Contributor
timestamp: September 05, 2024, 02:59:25 am
content: I'm sorry but you'll actually have to do some work. I am not your personal google. I have older standards and to access the latest it will be an IT request I can do tomorrow. Key phrase is "Conformity is checked by..."To avoid misunderstanding, you are asking for the clause saying the multimeter must work after transient testing? Like an IC died during the test and now displays "5.00V" with 600V applied, or it went blank?For transient testing mentions "Conformity is checked by evaluation of the RISK assessment documentation to assure that the RISKS have been eliminated or that only TOLERABLE RISKS remain."OP check for the relevant Part 2 for your product. Part 1 covers everything like lasers and some UV tanning beds etc. and you need to purchase the specific Part 2's.I have one example of what might be looked for from the Part 2, bold is my highlight for the basics, it's a steady-state (not transient) test:"Safety requirements for electrical equipment for measurement, control, and laboratory use — Part 2-030: Particular requirements for testing andmeasuring circuits""Conformity is checked by inspection and the following test, repeated three times on the same unit of equipment. If the test results in heating of any component, the equipment is allowed to cool before the test is repeated. If a device used for current limitation is damaged, it is replaced before the test is repeated.""The possible a.c. and d.c. short-circuit currents are calculated as the maximum RATED WORKING VOLTAGES for any TERMINAL divided by the impedance of the current-limited measuring circuit, taking the impedance of the test leads specified in 101.3.4 into account. The possible a.c. short-circuit current should not exceed the value in Table AA.1.""A voltage equal to the maximum RATED voltage for any TERMINAL is applied between the TERMINALS of the measuring circuit for 1 min. The source of the test voltage shall be able to deliver a current of at least the possible a.c. or d.c. short-circuit current as applicable.If the function or range controls have any effect on the electrical characteristics of the input circuit, the test is repeated with the function or range controls in every combination of positions.During and after the test, no HAZARD shall arise, nor shall there be any evidence of fire, arcing, explosion, or damage to impedance limitation devices or any component intended to provide protection against electric shock, heat, arc or fire, including the ENCLOSURE and traces on the printed wiring board.Any damage to a device used for current limitation shall be ignored if other parts of the equipment were not affected during the test."

author: Someone
author_rank: Super Contributor
timestamp: September 05, 2024, 03:22:00 am
content: Quote from: floobydust on September 05, 2024, 02:59:25 amYour bolded bit again repeats the underlying obligation, that protection is maintained. No obligation that accurate or correct readings/measurements are still provided. All that is about the protection from hazards, and as I said that is entirely separate to damage/destruction of functional pathways.Quote from: Someone on September 04, 2024, 11:45:27 pmFeels like you are clutching at a practical simplification of the standards, which although it is valid/safe/meets the standard is not the actual standard its self and can be excessively expensive/onerous to meet.

author: Cyclone1
author_rank: Newbie
timestamp: September 05, 2024, 05:28:34 am
content: Quote from: Whales on September 04, 2024, 02:37:14 amThe few DMM I looked at specified 1000VDC/750VAC with CAT II 300V rating on the input jack side. Could it be that the standard care about clearance/creepage based on the CAT rated max input voltage only? Like I only need 300V worth of creepage/clearance because its rated CAT II 300V?

author: Cyclone1
author_rank: Newbie
timestamp: September 05, 2024, 06:42:50 am
content: Quote from: floobydust on September 04, 2024, 08:01:43 pmThanks for your response! This safety stuff is really hard since I have never learned it before and the task just suddenly dropped on my lap and need to get it sorted. Besides, this standard is, how do I put it, isn't written very clearly and open for interpretation and is causing conflict, even among my colleagues. Its frustrating.QuoteI see you only mentioned the CAT rating specifications, and not the maximum input voltage. Does the standard requires only creepage/clearance designed to the CAT rating only? Since creepage are designed based on the working voltage, in your example, I needed creepage for 300V only even though the input can take up to 1000VDC (non-CAT rated)?QuoteI referenced the instrument I tore down and drawn this very rough diagram in the attachment. There are some differences in architecture between the DMMs but they are very similar. First thing I do is identify what are the accessible part. I believe its by default the probes.From the diagram, I concluded that the relay, switches and the isolated MOSFET driver requires creepage, since the input voltage is stressing this barrier and could short which could in turn could cause a shock. But not one of the DMM I looked at designed sufficient 1000V creepage for this component.Is my understanding of the safety standard correctly?On the other hand, I noticed the isolator, which I believe used for communication between the isolated and non-isolated circuit, have met the basic insulation. I wonder why this needs isolation, since the isolator does not see the 1000V input voltage directly.