Re: EN60065 - safety and audio in/out terminals

On 12 mar, 15:13, allem...@xxxxxxxxx wrote:
Hi to everybody!
I'm working developing an audio equipments that must comply with the
EN/IEC60065 safety requirements.
The device will be a Class I apparatus, so its external metallic
cabinet will be earthed.

Following the IEC standard requirements, I have to ensure the
dielectric withstanding strength between the ACCESIBLE conductive
parts and the mains line terminals.
My doubt is whether I have to consider the inpunt/output terminal as
accessible conductive parts or not.

As example, thinking on a preamplifier with male XLR output connector:
the inner contact of the XLR connector are to be consider as
accessible conductive parts?
If yes, I have to ensure the dielectric withstanding strength between
those and the mains?
That means I have to test its withstanding applying 1.5 kV AC (or 2.5
kV AC) to the XLR pins? That would be crazy, in my opinion...

Hello,

You have to insure that in a single fault condition, the equipment is
safe. Audio inputs and outputs (cable and connectors) do not provide
sufficient protection for the expected overvoltage, so yes you are
right, they may carry out High Pot testing between mains and audio
input/output.

You will probably have a transformer inside the cabinet. Imagine your
transformer has 100pF between Primary live and secondary (that is -
j32MOhm). This means that at 1500Vac, the current will be max 47uA.
When your input has 100 kOhm to DC ground, about 4.7V will be across
the input and DC ground, and 1500V will be across the winding
insulation of your transformer.

Probably you will have some form of ESD protection between inputs and
your DC ground on the PCB. In case of very high impedance circuits,
the ESD protection will take most of the 47uA.

Practically spoken, not everything is tested. When the transformer is
OK, many other things can be checked by inspection (clearance/
creepage, what happens when a wire breaks, flammability, etc). This
is the reason that many manufacturers use an already approved mains
adapter; this eliminates the need for High Pot testing on the low
voltage device itself.

When they want to test one input for checking the safety of the mains
transformer, you may probably short circuit the inputs. In addition,
the voltage is increased gradually so will not get transient
effects. Ones I joined a test at 4250Vdc where there was a discharge
between Live and PE, so in that case 4kV was between PE and the low
voltage input (bad result).

Hopes this takes away some of your worries,

Wim
PA3DJS
www.tetech.nl
without abc, you can use the pm if required.
.

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