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Standards for a PSU to be considered as "SELV"

Hi - quick standards question, for hobby purposes only:

Is a declaration of being "Class II" and within the appropriate voltage band, sufficient for a PSU to be considered as SELV for usage scenarios in BS7671?

I'm doing a Raspberry Pi project with my son to PWM drive some 30V LED outdoor fairly lights. So I'm choosing a PSU that's nice and safe.

The candidate PSU I have is this one: 30V PSU (RS) or possibly this one 30V PSU (-10C) for it's lower operating temperature (it's going to be in the shed, occasional drops below 0C possible)

First one is defined as Class II, it's 30V. It also claims medical approval. A whole bunch of quoted standards on the datasheet above. Apart from "Class II", not sure if I should be looking at any particular standard that defines it as meeting SELV PSU requirements. Isolation voltage is given as 4kV?

Second one claims very little but implies Class II by lack of protective conductor pin.

Pretty sure either is a good choice (noting operating temperature limits of the first), but academically I have been curious what defines a SELV PSU if it doesn't actually have the word SELV printed on it?

Many thanks as always for letting me tap the font of knowledge that this forum is :)

Tim

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0 broadgage over 5 years ago

My understanding is that the PSU must be so designed that the ELV output can not become connected to the mains input under fault or failure conditions.

In practice this means double or reinforced insulation between mains and ELV. For example the mains and ELV transformer windings must be on separated insulated formers, such that BOTH would have to fail to become dangerous.

AFAIK there is also a requirement that it must EITHER be protected against over current and overvoltage, OR that it must fail safely.

For example output overload blows a fuse=fine.

Output overload destroys the PSU without exposing the user to mains=fine

Output overload melts plastic internal insulation and allows the ELV output to connect to the mains=NOT FINE.

If the PSU is of reputable manufacture and is marked SELV and is CE marked, then that in my view is acceptable, you are not required to do your own tests regarding the veracity of the markings.

Just marked "ELV" is not in my view sufficient, for say lightly insulated equipment that should be connected to a SAFETY ELV source.
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0 broadgage over 5 years ago

My understanding is that the PSU must be so designed that the ELV output can not become connected to the mains input under fault or failure conditions.

In practice this means double or reinforced insulation between mains and ELV. For example the mains and ELV transformer windings must be on separated insulated formers, such that BOTH would have to fail to become dangerous.

AFAIK there is also a requirement that it must EITHER be protected against over current and overvoltage, OR that it must fail safely.

For example output overload blows a fuse=fine.

Output overload destroys the PSU without exposing the user to mains=fine

Output overload melts plastic internal insulation and allows the ELV output to connect to the mains=NOT FINE.

If the PSU is of reputable manufacture and is marked SELV and is CE marked, then that in my view is acceptable, you are not required to do your own tests regarding the veracity of the markings.

Just marked "ELV" is not in my view sufficient, for say lightly insulated equipment that should be connected to a SAFETY ELV source.
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Standards for a PSU to be considered as "SELV"

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