EN61010 Interpretation - Page 1
Forum section: electronics / projects

author: AndrewHodgson
author_rank: Contributor
timestamp: November 15, 2019, 12:37:36 pm
content: Hi,I'm unsure how to interpret the EN 61010 clearance requirements for secondary circuits derived from mains (Table 6) and wanted to know if someone could help me understand them.If i'm designing a product powered from 24V, do i use the values for mains voltage of <150 Vac RMS or the values for >150Vac RMS <300Vac RMS? I would say that in the UK, where the mains voltage is 240V RMS, you use >150Vac RMS <300Vac RMS values, but i'm not sure. Are the clearances about the mains voltage applied to the external powers supply, or the product power supply? I would have thought the clearances are related to the transients coupled across the isolation in the external power supply, so its about the mains for voltage for the external supply?Thanks in advance.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 15, 2019, 03:25:10 pm
content: Disclaimer: I've read 60950-1 but not 61010. I'm assuming there are general similarities.Is there anything specific about external power supplies, plug packs and the like? Most often, all safety issues are solved here.Your equipment is SELV, and you only need to meet functional insulation (or stronger if you're generating unsafe voltages and putting them in potentially accessible areas, but yeah). Which is in a different table I think. You will want to verify that the power supply offers adequate insulation (typically reinforced) for your use case.Tim

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 15, 2019, 03:53:59 pm
content: Quote from: T3sl4co1l on November 15, 2019, 03:25:10 pmI second that, from the short description the OP gave us. We may need additional info though, but I agree most of the burden would be on the mains to 24V power supply. If it's a separate, third-party PS that is already compliant, I agree you should only care for the requirements for SELV devices.

author: Neilm
author_rank: Super Contributor
timestamp: November 15, 2019, 05:47:02 pm
content: From memory, that table really referrs to the situation you have a step down transformer converting the mains to your 24 V. Any mains transients will still have an effect on the 24 V side hence you need clearances. If your 24 V is from a plug pack you don't need to worry about additional clearances.

author: floobydust
author_rank: Super Contributor
timestamp: November 15, 2019, 08:36:11 pm
content: The standard assumes mains transients are attenuated by power transformers, so they'll still exist on the secondary side but much smaller:6.7.3 Insulation for secondary circuits derived from MAINS CIRCUITS of OVERVOLTAGE CATEGORY II up to 300V6.7.3.1 General"In this standard, secondary circuits are circuits where separation from MAINS CIRCUITS is achieved by a transformer in which the primary windings are separated from the secondary windings by REINFORCED INSULATION, DOUBLE INSULATION, or a screen connected to the PROTECTIVE CONDUCTOR TERMINAL.NOTE These circuits are assumed to be subjected to lower TRANSIENT OVERVOLTAGE levels than the MAINS CIRCUIT."For your product, you must also know the Pollution Degree and what method of protection against electrical shock - grounded secondary, double-insulation, reinforced insulation etc. you are going with.On the mains primary-side, you'll still need to meet 61010 creepage/clearances from likely Table 4.Careful your transformer/SMPS/plugpack meets 61010, or you will have to get it tested- which is a very expensive surprise and not worth it.On the secondary side, use Clearances Table 6, knowing the mains voltage and OVC incoming to the power supply, and the secondary voltage.i.e. with 150-300VRMS mains, OVC II incoming and a 24VAC secondary use 33VAC for 0.52mm clearance. Creepage is Table 7, I'd use 25V or 32VRMS PDII for 0.04mm on the PC board.

author: AndrewHodgson
author_rank: Contributor
timestamp: November 16, 2019, 08:50:35 am
content: So to be clear, if i'm using a purchased SELV power supply with my product, the creepage and clearance values of table 6 and 7 apply because the attenuated transients are still coupled from the purchased power supply into my product? As long as the circuitry is on the secondary side, it does not matter whether the 24V was generated inside or outside the product? The column is 150-300V mains because we use 240V, if the product was being used in the US it would be 0-150 because they use 120V.Apologies, if i've miss understood.It is pollution degree II, OVCII, double isolation.Thanks for all your posts.

author: floobydust
author_rank: Super Contributor
timestamp: November 18, 2019, 12:18:43 am
content: 61010 clarity is not great, they don't define "derived from mains", or even "transformer". 61010-2-201 covers external power supplies in detail. It's your basic torture.I need to know more about the product - Metal enclosure? Mounted to anything grounded? Connects to anything else, like sensors? Is this PSU a wall-adapter, SMPS or 50/60Hz transformer? It depends if this is single or poly phase, PE ground in the PSU primary or not. I'm making probably too many assumptions...I looked at both 61010 and old 60950 to try figure out what the spacings and test voltages are, for your SELV secondary circuit.61010 clarity can be pretty bad sometimes and if applicable 6.7.3.1 says the secondary-side still needs increased spacings due to the (standard's) notion a transformer will still pass some of a mains transient. 850VAC RMS test voltage per 6.8 between foil wrap and secondary-side.But here the transformer is not located inside the product (it's in the plug pack). An SMPS will have a Y-capacitor that passes a common-mode impulse to the secondary side.The PSU has the double-insulation which is providing the protection against electric shock, output as a SELV circuit.Looking at 60950 2.10.3.7 the secondary-circuit transient voltage can be one category less i.e. Cat II 2,500V down to 1,500Vpk.So both standards appear to have the position a non earth grounded wall-adapter does not magically eliminate a mains transient, so secondary side spacings need to be greater than working voltage of 24V.Don't run with what I say, a mistake would be too costly and it's cheaper to just book a technical meeting for an hour with a 61010 certifier and pay the $350, after you have a list of questions.