John,
If the output is SELV earthed (in other standards PELV) then (as I read
60950-1) table 5B applies and test 3kV is ok. If you decide to use 5C
table then because of earthing you can use one level lower test voltage
(as I read Annex G) and you end also with 3kV test.
But there is no info about need to earth the 12V output of this supply,
and I have other reasons to not earth it.
We produce access door controller and we are supposed to specify a metal
box, power supply, battery to be used with our controller. I am just
trying to find if I can specify this one (I like it because of its small
dimensions).
As I understand PELV doesn't mean earthed but only not isolated from
Earth with basic isolation. It can be isolated with functional isolation
and it is PELV.
Where to find in 60950-1 how hard have to be earthing of SELV to allow
for using table 5B. In 5.2.2 there is only word connected. Does that
mean that any connection of 12V output to earth (even with 100m thin
wire) is enough to use table 5B?
Piotr
W dniu 2017-11-22 o 19:13, John Woodgate pisze:
We need to be very careful here. There is not a single definition of
'SELV'. Some definitions allow the LV circuit to be earthed, some do
not, and refer to 'Protected Extra-Low Voltage (PELV)' for SELV which
is earthed. Non-earthed SELV is OK for some purposes, but I don't
like it for situations where an insulation failure (which might not be
in the parts that are tested to 3 kV) allows the LV circuit to become
live and for that fault to persist indefinitely undetected, which I
think is your situation. For such applications I prefer PELV, and I
think your 3 kV test may be acceptable for PELV, depending on which
safety standard applies.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associateswww.woodjohn.uk
Rayleigh, Essex UK
On 2017-11-22 17:50, Piotr Galka wrote:
Dear safety experts,
Help me to make me sure that it is save to use the following power
supply:
http://www.meanwell.com/webapp/product/search.aspx?prod=DRC-40
to power 12V doorlock with not earthed 12V supply.
I think that from practical point of view it is save but how it looks
formally.
This supply is TUV EN60950-1 approved, and input to output is tested
with 3kVAC. There is no info if output is SELV or ELV.
Before asking them if their output is SELV I'd like to know if it has
to be SELV, or if from info I have I can find it is SELV. I wont to
use this case to learn myself more about safety.
Why I'm not sure.
1. I suppose that 12 doorlock manufacturer can use only functional
isolation betwean 12V and its metal casing as he can assume (I think)
that he gets safe voltage.
If I'm wrong with it let me know.
2. Then as doorlock metal casing can be touched by user than 12V have
to be SELV circuit I think.
3. I'm not sure if the 12V output from this supply is SELV - is it
enough to test the isolation with 3kV.
In EN 60950-1:2006 5.2.2 I understand that if output is not grounded
or there is no protective screen than table 5C should be used.
I assume not earthing 12V.
I don't know if there is protective screen inside but as I can
imagine such supply there have to be feedback and it is probably opto
feedback - so can there be metal screen betwean LED and opto element
and opto will work? I'm not sure if I understand well what is screen
in accordance with 2.6.1 e).
From Annex G I understand that for Overvoltage Category II transient
voltage (Europe) will be 2k5V and from table 5C I have 5kV test
needed. So 3kV written in datasheet looks being not enough.
All till now I have written assuming the Overvoltage Category II. But
reading Annex Z I'm not sure if access control system, as permanently
installed, is integral building wiring or not. It seems me more like
a fuse panel then permanently connected electric cooker. If category
III then I end with 8kV testing - much more than 3kV.
It is TUV approved and under Applications the producer lists Access
Systems so powering doorlock should be save. If it is true - where is
my mistake.
Best Regards
Piotr Galka
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