EN 61010 standard interpretation

[Darren DeBattista]

Hi,

I hope I'm posting on the correct board.

I'm designing a product which would need to be tested for compliance with the EN 61010-1 safety standard. I have a question mainly related to the interpretation of the tables related to clearance and creepage. Table 6 list the 'Clearance and test voltages for secondary circuits derived from mains circuits of overvoltage category II up to 300V'. Is this referring to the clearance between one track and another on the secondary side of a circuit? In other words, if I have an isolated 24V supply coming from flyback PSU connected to mains, should I keep each track connected to the 24V circuit at a clearance of 0.52mm as stated in this table (i'm referring to the clearance on tracks which are both on the secondary side and not between primary and secondary)?

Thanks

[Neilm]

It has been a while since I looked at this section - generally I work on things that measure the mains (different part of 61010). I think this refers to circuits derived from normal mains transformers that run at line frequency. This is because they will allow a some voltage through from a mains transient. What does table 6 say for 24V?

[Darren DeBattista]

Hi Neilm,

Thank you for your reply. As for what table 6 says, for 'Mains voltage, line-to-neutral, overvoltage category II of > 150V and <= 300V ac rms, it list the following: for

Secondary Working voltage                    Clearance                                 Test voltage (Vac rms)
16Vac_rms or 22.6Vdc                             0.50                                          840
33Vac_rms or 46.7Vdc                             0.52                                          850
50Vac_rms or 70Vdc                                0.53                                          860


As you can see, the secondary voltage is listed as iether AC or DC. This is why I though this may be related to clearance in between tracks which are both on the secondary circuit. What I find strange is that a clearance 0.52mm for a 24V tracks; I think its too much especially considering other PCBs I have seen.

[floobydust]

Need more information to see if Table 6 would apply.

What is the product's method of protection against electrical shock? Reinforced insulation or PE grounded secondary?
The 24VDC SMPS is your own design and the transformer as well?

[Darren DeBattista]

Hi floobydust,

Some more info about the product. The product will be a Class II product having a non conductive enclosure with no accessible parts and no PE connection. The power supply is a readily made Class II power supply having all the necessary (product) standards (EN 60950; safety, EN61000-4-2,3,4,5,6,8,11 EMC etc...). This power supply already has reinforced insulation although it is not really needed. My way of design was to have a basic insulation between mains circuit and the DC (secondary) circuit and than implement a supplementary insulation using the plastic enclosure.

My issue related with table 6 is to know if table 6 relates to the secondary isolated voltage circuit (my SMPS output) or if I'm missing something since that I'm seeing the 0.52mm needed for a 24V circuit a bit excessive. Also, the output of my third party PSU is 5V dc and table 6 list voltage from 22.6Vdc upwards. Should this mean that, if table 6 applies for the secondary circuit in my case, I don't have a minimum clearance since the voltage is lower than 22.6V?

Thanks

[floobydust]

Designing to 61010 is very difficult. I find it's a poorly written standard with everything from lasers, xrays, multimeters in there.

May be best to collect and write down several questions, and have a meeting or conference call with the agency to get answers during a technical consultation. It's very costly to go down the wrong road. Take my ramblings very lightly.

For a secondary working voltage of 24V, I would follow:
Table 7 and K.13 gives PCB creepage 0.04mm/1.6mil
Table 6 gives clearance of 0.52mm/20mil (PD2). There is a minimum clearance K.2.2 of 0.2mm (PD2).

If product size is an issue, Annex H and conformal coating (takes you to PD1) or potting can lower the 0.52mm, or you can route using PCB inner layers as they have insulation.

I'm hearing the product is still safe (under one fault) with the 24V rails floating to hazardous live. There are no user-accessible parts under normal use. This is a black box with only mains coming in, is this correct? (it seems unusual, sensor/field wiring or a LCD touch screen or buttons, switches etc. I would expect).

The plastic enclosure as supplementary insulation may be a troublesome approach as the electrical specs and approvals are always not there to qualify it as an approved insulator. I don't know how big a company you are, if the enclosure is "off the shelf" or your custom design.

I've had to prove the plastic used, thickness, flammability, rigidity, tracking index, etc. - and that all (tolerances) of it was controlled by the enclosure manufacturer, that they could not change anything without you knowing.

[Darren DeBattista]

Hi floobydust,

The standard is poorly written indeed. The wording is to vague, never giving a clear definition of meaning (most probably cause it was written by lawyers not engineers). Anyway....
As how the product is still safe, I can't disclose much but what I can say is that the product is very similar to a smart light which should light up when detecting a movement/presence. Hence, there is no interaction by the user (except for the installer).

Thanks for bringing the enclosure issue up. Its actually an of the shelve enclosure which I should go more in dept regards its specs for approval as a supplementary insulation (would also need to check clearances from live circuits to enclosure etc..).

As to my original issue, what I was in doubt about is if table 6 does indeed apply to any secondary circuit coming out from a PSU. My thought is that if I have a stanfard transformer, rectifier and smoothing cap PSU, than yes I have to use table 6. But considering that the intro to table 6 specify the following (I qoute):

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.


Is table 6 also needed to be followed in case of using a flyback SMPS considering that its not directly derived from a transformer and hence overvoltage values on the secondary due to overvoltage on mains supply is relatively much lower?

bdw, thanks for pointing the 0.2mm absolute minimum clearance for PD2.

Thanks

[floobydust]

As Neilm mentioned, the secondary spacings are based on the mains transient making it through a "power transformer" to the secondary.
For a 50/60Hz transformer, inter-winding capacitance and leakage inductance (coupling) lower the impulse but some still passes through.

I follow those spacings, even if there is a question at hand. 0.52mm clearance is not terribly big and IPC, IEC 60664 are in line with that.
Running out of room in a product (for increasing spacings after findings) is the death knell for the project. Always leave extra room.

Clause K.3.1 (not table, not figure) addresses SMPS operating over 30kHz, and different spacings.


I would rely on the power supply's reinforced insulation.
Careful with Taiwan PSU modules, they don't achieve EMC claims without additional external filtering, shown on the app notes in a cryptic diagram.
I find an extra MOV is required to pass over-voltage tests, most PSU modules don't have one adequate.

Your clear plastic window, it's important. Not a cutout you machine-in an approved enclosure and glue a window in. Then you have to ball test it and all that.
I have used white plastic enclosures with a clear lid and put a sticker behind, to mask off most of it (lid) except for an LED display window.

[Darren DeBattista]

Hi  floobydust,

Thanks again for the reply. So if I understand correctly, if I have an SMPS connected to mains at < 300VACrms working at a frequency higher than 30kHz, I have to use table 4 for primary-to-primary and primary-to-secondary clearance while I have to use table K.17 for secondary-to-secondary clearance.

I think I know to which types of Taiwan PSU modules you are referring. They give two external filters circuits according to if you need class A or class B compliance. The one I used is from a reputable manufacturer from Taiwan too but it lists that it complies with EN55022 Class B without additional external filtering. It also complies with EN 60950-1 and is an encapsulated Class II module (in fact I think it doesn't even need any external safety devices like fuse or fusable resistor. I also confirmed with the manufacturer that it has an internal fuse). They give all the certifications and reports on their website. I'm trusting them due to these certificates and reports but if you have some bad experience even with reputable manufacturers please don't hesitate to tell me.

As for the enclosure,the front part is actually a solid 4mm thick glass being covered in part with solid paint and in part with transflective paint to transmit light. It would be glued to a 'structure' using 3M double sided tape and the 'structure' + glass assembly attached to the enclosure with a clipping action and would be necessary to remove it (and exposing the secondary circuit) only during installation. So there are no accessible parts during normal use but the secondary is accessible by the installer/service personal during installation (I still have to check regarding this, but the PSU should already be with reinforced insulation so I could go for a reinforced insulation between primary and secondary just to be on the safe side).

Thanks again for your help